The Hypertension Institute of Nashville offers the following clinical testing services:

Ambulatory Electrocardiogram (Holter Monitor)

Ambulatory Electrocardiogram (Holter Monitor)

An ambulatory electrocardiogram (EKG or ECG) records the electrical activity of your heart while you do your usual activities. Ambulatory monitors are referred to by several names, including ambulatory electrocardiogram, ambulatory EKG, Holter monitoring, 24-hour EKG, or cardiac event monitoring.

Many heart problems become noticeable only during activity, such as exercise, eating, sex, stress, bowel movements, or even sleeping. A continuous 24-hour recording is more likely to detect any abnormal heartbeats that occur during these activities.

Many people have irregular heartbeats (arrhythmias) from time to time. The importance of irregular heartbeats depends on the type of pattern they produce, how often they occur, how long they last, and whether they occur at the same time you have symptoms. Because arrhythmias can occur off and on, it may be difficult to record an arrhythmia while you are in Dr. Houston’s office.

There are several different types of ambulatory monitors.

Continuous recorders

The most common type is the continuous recorder (such as the Holter monitor). It provides a 24 to 72 hour record of the electrical signals from your heart. A standard EKG monitors only 40 to 50 heartbeats during the brief period you are attached to the machine. A continuous recorder monitors about 100,000 heartbeats in 24 hours and is likely to find any heart problems that happen with activity.

Another type of continuous recorder can be implanted under the skin of the chest. This recorder can be kept in your chest for more than a year to record the electrical signals from your heart.

Intermittent recorders

Another kind of ambulatory EKG monitoring is the intermittent recorder, which is used when symptoms of an abnormal heart rhythm do not occur very often. An intermittent recorder can be used for a longer time than a continuous recorder. The information collected by an intermittent recorder can often be sent over the phone to the Heart Station.

Two types of intermittent recorders are available:

  1. Loop recorders. A loop recorder constantly records your heartbeats. When you have symptoms, you press a button on the monitor to record your heart rhythm. Loop recorders also save a small amount of information about how your heart was beating when you pressed the recording button (presymptom recording). This feature is especially useful for people who lose consciousness when their heart problems occur and can press the button only after they wake up.
  2. Event monitor. This small device is used only when symptoms of the heart problem occur. You are not attached to the machine. One type is worn on the wrist like a watch. When symptoms occur, you press a button to start the EKG recording. The other type is a device that you carry where you can reach it easily, such as in your purse or pocket. When symptoms occur, you press the back of the device against your chest and then press a button to start the recording. The back of the device has small metal discs that work like electrodes. These handheld monitors can be very small (some are about the size and shape of a credit card).

Why It Is Done?

Ambulatory EKG monitoring is done to:

  • Look for and record irregular heartbeats that occur intermittently or during certain activities.
  • Find out what is causing chest paindizziness, or fainting. These are symptoms of possible heart problems.
  • Look for poor blood flow to your heart muscle (ischemia).
  • Check to see if treatment for an irregular heartbeat is working.

How It Is Done?

Continuous recorders

For this test, you wear a lightweight, battery-operated tape recorder (monitor) on a strap over your shoulder or around your waist. The recorder is connected by wires to small metal discs (electrodes) taped to your chest. The electrodes detect the electrical signals from your heart. A clock is connected to the recorder so you can note what time it is when you have any symptoms.

You will be fitted with the recorder and electrodes by a technician in the Heart Station.

  • Several areas on your chest may be shaved and cleaned, and then a small amount of electrode paste or gel will be applied to those areas.
  • The electrode pads will then be attached to the skin of your chest, with thin wires connecting the electrodes to the monitor.
  • You may be hooked up briefly to a standard EKG machine to ensure that the electrodes are working properly.

While wearing the continuous recorder, you will also be asked to keep a diary of all your activities and symptoms, including the type of activity you were doing and the time your symptoms started. In the diary, write down the exact times when you exercise, climb stairs, eat, urinate, have a bowel movement, have sex, sleep, get emotionally upset, take medicine, or perform other activities. If you have any symptoms of heart problems, such as dizziness, fainting, chest pain, or palpitations, push the event-marker button on the recorder to mark it and write down the exact time and how long the symptom lasts. For example, you might write: “12:30 p.m. Ate lunch. 1:00 p.m. Argument with boss, had chest tightness for several minutes.”

When you sleep, try to stay on your back with the recorder carefully positioned at your side so that the electrodes are not pulled off. If one of the electrodes or lead wires comes loose, a light on the monitor will flash. Press on the center of each electrode to see if you can restore the contact. Call the Heart Station if one of the electrodes comes off and you can’t get it to stay on.

While you are wearing a monitor, try to stay away from magnets, metal detectors, high-voltage areas, garage door openers, microwave ovens, and electric blankets. Do not use an electrictoothbrush or shaver. Signals from these types of electronic equipment can sometimes interfere with the recording.

At the end of the recording period (usually 24 hours), you will return to the Heart Station to have the electrodes removed, or you may be able to remove the electrodes yourself. The recorded tape will be read by computer to provide information about your heart rate, the frequency of your heartbeats, and any irregularities.

After the monitoring period, your doctor will compare the timing of your activities and symptoms with the recorded heart pattern. The accuracy and usefulness of this test depend on how carefully you record your activities and symptoms and the times they occurred.

Intermittent recorders

The procedure for intermittent recording depends on the type of monitor used.

  • Loop recorder. Electrodes will be attached to your chest in the same way as a continuous recorder, and you will start the recorder when you have symptoms of a heart problem. If you pass out, you should start the recorder as soon as you wake up. Also, be sure a friend or family member knows how to start the recorder if you pass out.
  • Event monitor. You will carry the small recording device where you can reach it quickly, such as in your pocket or purse. When you have symptoms of a heart problem, press the small metal discs on the back of the monitor (electrodes) against your chest.

You may be instructed to call Dr. Houston’s office while you are having symptoms or soon after you record your heart rhythm so that the information on the monitor can be analyzed right away.


An ambulatory electrocardiogram (EKG or ECG) is a test that records the electrical signals that control your heartbeat while you do your everyday activities. Results of ambulatory EKG monitoring usually are interpreted by a cardiologist. The results are generally available in a few days.

Ambulatory electrocardiogram (EKG or ECG)
Normal: No abnormal heart rhythms are found in the EKG information collected by the recorder. Your heart rate may go up when you are active and go down when you are sleeping.
  • Many kinds of irregular heartbeats can be detected by ambulatory monitoring.
  • Abnormal slow or fast heart rhythms are detected. Alternating slow and fast rhythms may also occur occasionally.
  • A slow heart rhythm in a person with a pacemaker may mean that the pacemaker is not working correctly.
  • Abnormal patterns may mean that the heart muscle is not getting enough oxygen (ischemia) because the arteries feeding the heart are too narrow.

The results of ambulatory heart monitoring are compared with your medical history, symptoms, and other test results. You may need to have the test repeated if the results aren’t clear.

What Affects the Test?

You may not be able to have the test or the results may not be helpful if:

  • You do not keep a detailed diary of your daily activities and symptoms. The intermittent recorder will give accurate results only if you remember to start the recorder when symptoms of possible heart problems occur.
  • The electrodes are not in the right spot.

Ambulatory Event Monitor

Ambulatory Event Monitor

An ambulatory electrocardiogram (EKG or ECG) records the electrical activity of your heart while you do your usual activities. Ambulatory monitors are referred to by several names, including ambulatory electrocardiogram, ambulatory EKG, Holter monitoring, 24-hour EKG, or cardiac event monitoring.

Many heart problems become noticeable only during activity, such as exercise, eating, sex, stress, bowel movements, or even sleeping. A continuous 24-hour recording is more likely to detect any abnormal heartbeats that occur during these activities.

Many people have irregular heartbeats (arrhythmias) from time to time. The importance of irregular heartbeats depends on the type of pattern they produce, how often they occur, how long they last, and whether they occur at the same time you have symptoms. Because arrhythmias can occur off and on, it may be difficult to record an arrhythmia while you are in the doctor’s office.

There are several different types of ambulatory monitors.

Intermittent recorders

The procedure for intermittent recording depends on the type of monitor used.

  • Loop recorder. Electrodes will be attached to your chest in the same way as a continuous recorder, and you will start the recorder when you have symptoms of a heart problem. If you pass out, you should start the recorder as soon as you wake up. Also, be sure a friend or family member knows how to start the recorder if you pass out.
  • Event monitor. You will carry the small recording device where you can reach it quickly, such as in your pocket or purse. When you have symptoms of a heart problem, press the small metal discs on the back of the monitor (electrodes) against your chest.

You may be instructed to call your doctor, clinic, or hospital while you are having symptoms or soon after you record your heart rhythm so that the information on the monitor can be analyzed right away.

Ankle-Brachial Index Test

Ankle-Brachial Index Test

This test is done by measuring blood pressure at the ankle and in the arm while a person is at rest. Measurements are usually repeated at both sites after 5 minutes of walking on a treadmill.

The ankle-brachial index (ABI) result is used to predict the severity of peripheral arterial disease (PAD). A slight drop in your ABI with exercise means that you probably have PAD. This drop may be important, because PAD can be linked to a higher risk of heart attack or stroke.

Why It Is Done

This test is done to screen for peripheral arterial disease of the legs. It is also used to see how well a treatment is working (such as medical treatment, an exercise program, angioplasty, or surgery).


The ABI result can help diagnose peripheral arterial disease (PAD). A lower ABI means you might have PAD. A slight drop in the ABI with exercise, even if you have a normal ABI at rest, means that you probably have PAD.


A normal resting ankle-brachial index is 0.9 to 1.3. This means that your blood pressure at your ankle is the same or greater than the pressure at your arm, and suggests that you do not have significant narrowing or blockage of blood flow.


A resting ankle-brachial index of less than 0.9 is abnormal. If the ABI is:

  • 0.41 to 0.9, you likely have mild to moderate peripheral arterial disease.
  • 0.4 or below, you likely have severe peripheral arterial disease.

What To Think About

You may experience leg pain during the treadmill portion of the test if you have peripheral arterial disease (PAD).

Undiagnosed arterial disease in the arms can cause inaccurate test results.

Blood pressure readings may not be accurate when the blood vessel being measured is hardened by calcium (calcified). Arteries may calcify more than usual if you have diabetes or kidney problems (renal insufficiency).

A very abnormal ABI test result may require more testing to determine the location and severity of PAD that might be present.

Bone Mineral Density

Bone Mineral Density

A bone mineral density (BMD) test measures the density of minerals (such as calcium) in your bones using a special X-ray or computed tomography (CT) scan. This information is used to estimate the strength of your bones.

We all lose some bone mass as we age. Bones naturally become thinner (called osteopenia) as you grow older because existing bone is broken down faster than new bone is made. As this occurs, our bones lose calcium and other minerals and become lighter, less dense, and more porous. This makes the bones weaker and increases the chance that they might break (fracture).

With further bone loss, osteopenia leads to osteoporosis. So the thicker your bones are, the longer it takes to get osteoporosis. Although osteoporosis can occur in men, it is most common in women older than age 65.

If your bone density is lower than normal, you can take steps to increase your bone strength and reduce your chances of having a fracture. Some ways to increase bone density and strength include combining calcium and vitamin D supplements with weight-bearing exercise (such as walking), weight training (such as lifting weights or using weight machines), and using medicines such as calcitonin (Miacalcin), alendronate (Fosamax), risedronate (Actonel), or ibandronate (Boniva).

There are several different ways to measure BMD.

Dual-energy X-ray absorptiometry (DEXA). This is the most accurate way to measure BMD. It uses two different X-ray beams to estimate bone density in your spine and hip. Strong, dense bones allow less of the X-ray beam to pass through them. The amounts of each X-ray beam that are blocked by bone and soft tissue are compared to each other. DEXA can measure as little as 2% of bone loss per year. It is fast and uses very low doses of radiation. Single-energy X-ray absorptiometry (SXA) may be used to measure heel and forearm bone density, but SXA is not used as often as DEXA.

Why It Is Done

A bone mineral density (BMD) test is suggested for:

  • All women who are age 65 or older, and younger women who are at increased risk for broken bones caused by osteoporosis.1
  • Older men, and men with other risk factors for osteoporosis.2
  • Men and women who have hyperparathyroidism.
  • Men and women who have been taking corticosteroids, such as prednisone, for a long time.

Follow-up of how well treatment for osteoporosis is working for men and women being treated for 2 years or longer.


A bone mineral density (BMD) test measures the density of minerals (such as calcium) in your bones using a special X-ray or computed tomography (CT) scan. Results are usually available in 2 to 3 days.

Results of bone mineral density tests can be reported in several ways.


Your T-score is your BMD compared to the average score of a healthy 30-year-old. It is expressed as a standard deviation (SD), which is a statistical measure of how closely each person in a group is to the average (mean) of the group. The average BMD is determined by measuring the bone density of a large group of healthy 30-year-olds (young adult reference range). BMD values are then reported as a standard deviation from the mean of this reference group. Almost all 30-year-old people have a BMD value within 2 standard deviations of this mean.

  • A negative (-) value indicates that you have thinner bones (lower bone density) than an average 30-year-old. The more negative the number is, the less bone density you have compared with an average 30-year-old.
  • A positive (+) value indicates that your bones are thicker and stronger than an average 30-year-old.

The following table contains the World Health Organization’s definitions of osteoporosis based onbone mineral density T-scores.

Bone mineral density
Normal: Less than 1 standard deviation (SD) below the young adult reference range (more than -1)
Low bone mass (osteopenia): 1 to 2.5 SDs below the young adult reference range (-1 to -2.5)
Osteoporosis: More than 2.5 SDs below the young adult reference range (-2.5 or less)

If your bone mineral density test result is low:

  • You may have osteoporosis. Doctors usually use the lowest T-score to diagnose osteoporosis. For example, if your T-score at your spine is -3 and your T-score at your hip is -2, the spine T-score would be used to diagnosis osteoporosis.

You have a higher-than-average chance of breaking a bone. The more negative your T-score, the greater your chances of breaking a bone during a fall or from a minor injury. Every change of 1 SD means a twofold increase in the risk of fracture at that site. For example, if you have a T-score of -1, your chances of having a broken bone are 2 times greater than if your T-score was 0. Low BMD values may be caused by other problems, including:


Your BMD value may also be compared to other people of your age, sex, and race. This is called your Z-score. It is given in standard deviations (SD) from the average value for your age group.

  • A negative (-) value means that your bones are thinner (lower bone density) and weaker than most people in your age group. The more negative the number is, the less bone density you have compared with others in your age group.
  • A positive (+) value means that your bones are thicker and stronger than most people in your age group.

What Affects the Test

Reasons you may not be able to have the bone mineral density (BMD) test or why the results may not be helpful include:

  • Inability to be correctly positioned during the test.
  • Having a broken bone in the past. This can cause falsely high BMD results.
  • Arthritis of your spine. In this case, the changes caused by arthritis in the spine may not make the spine the best place to measure for osteoporosis.
  • Metal implants from hip replacement surgery or hip fracture.
  • Having an X-ray test that uses barium within 10 days of the BMD test.

Cardiac Diagnostic Tests

Cardiac Diagnostic Tests

New and advanced diagnostic tests and tools are constantly being introduced to further understand the complexity of disease, injury, and congenital or acquired abnormalities. The following are just a few of the diagnostic tests that have been used/are being used to further understand and identify cardiovascular disease. For more specific information, consult your cardiologist or physician.

  • Electrocardiogram (ECG or EKG)
    A test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias), and detects heart muscle damage.
  • Signal Average Electrocardiogram (SAE)
    A test that is much like an ECG, but takes longer because it records more information related to abnormal electrical activity.
  • Stress Test (usually with ECG; also called treadmill or exercise ECG)
    A test that is given while a patient walks on a treadmill or pedals a stationary bike to monitor the heart during exercise. Breathing and blood pressure rates are also monitored. A stress test may be used to detect coronary artery disease, and/or to determine safe levels of exercise following a heart attack or heart surgery.
  • Echocardiogram (also known as echo)
    A noninvasive test that uses sound waves to produce a study of the motion of the heart’s chambers and valves. The echo sound waves create an image on the monitor as an ultrasound transducer is passed over the heart.
  • Transesophageal Echocardiogram (TEE)
    A test in which a small transducer is passed down the esophagus to provide a clearer image of heart structures.
  • Positron Emission Tomography (PET) Scan
    A nuclear scan that gives information about the flow of blood through the coronary arteries to the heart muscle.
  • PET F-18 FDG (Fluorodeoxyglucose) Scan
    A specialized PET scan which uses a form of glucose to help determine which heart tissue, if any, has permanent damage due to decreased blood flow. It may be used after a heart attack to determine which procedure, such as angioplasty or stenting of the coronary arteries or bypass surgery, may be beneficial.
  • Thallium Scans or Myocardial Perfusion Scans
    • Resting SPECT Thallium Scan or Myocardial Perfusion Scan
      A nuclear scan given while the patient is at rest that may reveal areas of the heart muscle that are not getting enough blood.
    • Exercise Thallium Scan or Myocardial Perfusion Scan
      A nuclear scan given while the patient is exercising that may reveal areas of the heart muscle that are not getting enough blood.
    • Adenosine or Persantine Thallium Scan or Myocardial Perfusion Scan
      A nuclear scan given to a patient who is unable to exercise to reveal areas of the heart muscle that are not getting enough blood. Special medications which stress the heart, like exercise, may be given.
    • MUGA Scans/Radionuclide Angiography (RNA) Scans
    • Resting Gated Blood Pool Scan (RGBPS), Resting MUGA, or Resting Radionuclide Angiography
      A nuclear scan to see how the heart wall moves and how much blood is expelled with each heartbeat, while the patient is at rest.
    • Exercise Gated Blood Pool Scan, Exercise MUGA, or Exercise Radionuclide Angiography
      A nuclear scan to see how the heart wall moves and how much blood is expelled with each heartbeat, just after the patient has walked on a treadmill or ridden on a stationary bike.
  • Holter Monitor
    A small, portable, battery-powered ECG machine worn by a patient to record heartbeats on tape over a period of 24 to 48 hours – during normal activities. At the end of the time period, the monitor is returned to the physician’s office so the tape can be read and evaluated.
  • Event Recorder
    A small, portable, battery-powered machine used by a patient to record ECG over a long period of time. Patients may keep the recorder for several weeks. Each time symptoms are experienced, the patient presses a button on the recorder to record the ECG sample. As soon as possible, this sample is transmitted to the physician’s office by telephone hookup for evaluation.
  • Tilt Table Test
    A test performed while the patient is connected to ECG and blood pressure monitors and strapped to a table that tilts the patient from a lying to standing position. This test is to determine if the patient is prone to sudden drops in blood pressure or slow pulse rates with position changes.
  • Electrophysiology Study
    A test in which insulated electric catheters are placed inside the heart to study the heart’s electrical system.
  • Cardiac Catheterization (also called Coronary Angiogram)
    A test in which a small catheter (hollow tube) is guided through a vein or artery into the heart. Dye is given through the catheter, and moving x-ray pictures are made as the dye travels through the heart. This comprehensive test shows: narrowings in the arteries, outside heart size, inside chamber size, pumping ability of the heart, ability of the valves to open and close, as well as a measurement of the pressures within the heart chambers and arteries.
  • Magnetic Resonance Imaging (MRI) of the Heart
    A diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body. MRI of the heart may be used to evaluate the heart valves and major vessels, detect coronary artery disease and the extent of damage it has caused, detect the presence of plaque causing blockages of the coronary arteries, evaluate congenital defects, and detect the presence of tumors or other abnormalities. The cardiac MRI may be used prior to other cardiac procedures such as angioplasty or stenting of the coronary arteries and cardiac or vascular surgery.
  • Magnetic Resonance angiography (MRA) of the Heart
    A specialized type of MRI procedure used to evaluate blood vessels in the heart.

Cardiac Perfusion Scan (Thallium Stress Test)

Cardiac Perfusion Scan (Thallium Stress Test)

A cardiac perfusion scan measures the amount of blood in your heart muscle at rest and during exercise. It is often done to find out what may be causing chest pain. It may be done after aheart attack to see if areas of the heart are not getting enough blood or to find out how much heart muscle has been damaged from the heart attack.

During the scan, a camera takes pictures of the heart after a special test medicine (radioactive tracer) is injected into a vein in the arm. The tracer travels through the blood and into the heart muscle. As the tracer moves through the heart muscle, areas that have good blood flow absorb the tracer. Areas that do not absorb tracer may not be getting enough blood or may have been damaged by a heart attack.

Two sets of pictures may be made during a cardiac perfusion scan. One set is taken while you are resting. Another set is taken after your heart has been stressed, either by exercise or after you have been given a medicine. The resting pictures are then compared with the stress images.

This test is also known by other names including myocardial perfusion scan, myocardial perfusion imaging, thallium scan, sestamibi cardiac scan, and nuclear stress test.

Why It Is Done

A cardiac perfusion scan is done to:

  • Find the cause of unexplained chest pain or chest pain brought on by exercise.
  • Check for the location and amount of damage caused by a heart attack.
  • Identify coronary artery disease (CAD).
  • Help make treatment decisions for a person with CAD.
  • Check to see that the heart is getting enough blood after heart surgery or angioplasty.
  • Identify a congenital heart defectand determine how serious it is. These scans may also be done following surgery to correct a congenital heart defect.

How To Prepare

Before a cardiac perfusion, tell Dr. Houston if you:

  • Are taking any medicines, including erection-enhancing medicines (such as Cialis, Levitra, or Viagra). You may need to take nitroglycerin during this test, which can cause a serious reaction if you have taken an erection-enhancing medicine within the previous 48 hours. Ask your doctor whether you need to stop taking any of your other medicines before the test.
  • Are allergic to any medicines or anesthetics.
  • Are or might be pregnant.
  • Are breast-feeding. Use formula and throw out your breast milk for 1 to 2 days after the scan.

Do not eat or drink for at least 3 hours before a cardiac perfusion scan. If you are having a stress scan, avoid alcohol, tobacco, caffeinated beverages, and nonprescription medicines for at least 24 hours before the test.

Wear comfortable shoes and loose shorts or pants suitable for exercise. Remove all jewelry before the test.

How It Is Done

A cardiac perfusion scan is usually done in a hospital radiology or nuclear medicine department, a doctor’s office, or at an outpatient clinic. The test is done by a Cardiologist and technologist trained in nuclear medicine.

Resting scan

For resting scans, in which you do not exercise, you will be asked to remove your clothing above the waist, and you will be given a hospital gown to wear. Four electrodes will be attached to your chest to keep track of your heartbeats.

For a resting scan, the injection site on your arm will be cleaned and an elastic band will be placed around your upper arm. Then a small amount of the radioactive tracer is injected, usually into a vein on the inside of your elbow.

You will lie on your back on a table with a large camera positioned above your chest. The camera records the tracer’s signals as it moves through your blood. The camera does not produce any radiation, so you are not exposed to any additional radiation while the scan is being done.

You will be asked to remain very still during each scan, which takes 5 to 10 minutes. The camera will move to take more pictures at different angles. Several scans will be taken.

The entire test takes 30 to 40 minutes, after which you can resume your normal activities.

Stress scan using medicine

The stress scan is done in two parts. In many hospitals, the first images are taken while the person is at rest. Then a second set of images is taken immediately after the person is given a medicine such as adenosine, which makes the heart respond like it would to exercise. A stress test with medicine is usually used when a person cannot exercise for some reason.

For this test, you will be asked to sit or lie on the examining table and you will be given a routine electrocardiogram (EKG or ECG), which takes about 5 to 10 minutes.

Then the medicine is injected into your arm. You may get a headache and feel dizzy, flushed, and nauseated from the medicine, but these symptoms usually do not last long. Additional EKGs and blood pressure measurements are often taken. After the medicine takes effect (about 4 minutes), a small amount of radioactive tracer is injected. You will lie down on a table for a set of scans. The camera records the tracer’s signals as it moves through your blood. The camera does not produce any radiation, so you are not exposed to any additional radiation while the scan is being done.

Sometimes more pictures are taken after you rest for 2 to 4 hours. You may resume your normal diet and activities after the final set of scans.

Stress scan using exercise

For stress scans using exercise, your heart rate will be checked with an electrocardiogram (EKG or ECG). Because EKG electrodes need to be attached to the chest to check the heart, men are usually bare-chested and women usually wear a bra, gown, or loose shirt. For more information, see the medical test Electrocardiogram.

The exercise stress scan is done in two parts. First a set of resting images is taken, then a set of stress images is taken immediately after exercise. In many hospitals, first resting pictures are taken using one type of tracer. More pictures are taken using a different tracer after your heart has been stressed by exercise.

In this stress test, you exercise on a treadmill or stationary bike. Your heart rate will be checked during the test with standard electrocardiography. Your blood pressure is checked using a blood pressure cuff placed on your arm. For more information, see the medical tests Exercise Electrocardiogram and Electrocardiogram.

You will begin by walking or pedaling slowly and easily. Every few minutes, the speed or incline of the treadmill or resistance of the bike may be increased. You will exercise until you need to stop or until you reach a suitable heart rate. At that point, a different tracer medicine is injected. You will probably continue to exercise for an additional 30 to 60 seconds to circulate the radioactive tracer.

You will then lie down on a table for scanning. Each scan takes 5 to 10 minutes. The camera does not produce any radiation, so you are not exposed to any additional radiation while the scan is being done.

Sometimes more pictures are taken after you rest for 30 minutes to 4 hours. You may usually resume your normal diet and activities after the final set of scans.

In some hospitals, a second injection of radioactive tracer is repeated several hours after exercise and before the final image. You may be asked to return 24 hours after the test to have another set of pictures taken.

How It Feels

The cardiac scanning test itself is painless.

  • You may feel a brief stinging or burning sensation when the needle is inserted into the vein in your arm.
  • You may be uncomfortable lying still for an extended period of time on the table during the scans.
  • If medicine to stress your heart is used, you may have symptoms of mild nausea, headache, dizziness, flushing, or chest pain (angina). These symptoms only last a few minutes.
  • If you are asked to exercise, you may have chest pain, breathlessness, lightheadedness, aching in your leg muscles, and fatigue. Report these to the technician. If the symptoms are severe, the exercise part of the test may be stopped.


Cardiac perfusion scans are usually safe. There is always a slight chance of damage to cells or tissue from radiation, including the low levels of radiation used for this test. But the chance of damage from the radiation is usually very low compared with the benefits of the test.

The risk of exercise depends on the condition of your heart and your general level of health. The risks include:

  • Fainting.
  • Chest pain.
  • An irregular heartbeat.
  • Heart attack. There is a slight risk that death may result if a heart attack occurs during the test.

After the test

Call 911 or other emergency services immediately if you develop:


A cardiac perfusion scan measures the amount of blood in your heart muscle at rest and during exercise. Test results are usually available within 1 to 3 days.

Cardiac perfusion scan
Normal: The radioactive tracer is evenly distributed throughout your heart muscle.
No areas of abnormal tracer absorption are present.
Abnormal: Some areas of heart muscle are not getting enough blood (ischemia). This may mean that the heart has been damaged or that coronary artery disease is present.
The heart is enlarged and the left pumping chamber (ventricle) is not working well.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • A recent, serious heart attack.
  • Inflammation of the heart, such as myocarditis or sarcoidosis.
  • Bruising of the heart muscle (cardiac contusion).
  • Weakening of the heart muscle.
  • Stiffening of the heart muscle (myocardial fibrosis).
  • A severely narrowed heart valve.
  • Implanted cardiac devices, such as a pacemaker.
  • A condition that makes it difficult to exercise, such as lung disease, arthritis, or a neuromuscular problem.
  • Some medicines, such as dipyridamole (Persantine) and pentoxifylline (Trental).
  • Severe electrolyte imbalances (especially calcium, potassium, sodium, or magnesium).
  • Pregnancy or breast-feeding (except in an emergency).

Test results may be difficult to interpret in scans done on women with large breasts.

Cardiac Scan (MUGA Scan)

Cardiac Scan (MUGA Scan)

A cardiac blood pool scan shows how well your heart is pumping blood to the rest of your body. During this test, a small amount of a radioactive substance called a tracer is injected into a vein. A gamma camera detects the radioactive material as it flows through the heart and lungs.

The percentage of blood pumped out of the heart with each heartbeat is called the ejection fraction. It provides an estimate of how well the heart is working.

There are two types of cardiac blood pool scans.

First-pass scan. This scan makes pictures of the blood as it goes through the heart and lungs the first time. A first-pass scan can be used in children to look for heart problems that have been present since birth (congenital heart disease).

Gated scan or multigated acquisition (MUGA) scan. This scan uses the electrical signals of the heart to trigger the camera to take a series of pictures that can be viewed later like a motion picture. The pictures record the heart’s motion and determine if it is pumping (contracting) properly. MUGA scanning may take 2 to 3 hours to obtain all the needed views and can be done both before and after you exercise. You may be given nitroglycerin to see how your heart responds to this medicine. MUGA scanning may be done after a first-pass scan. It is usually not done on children.

Why It Is Done

A cardiac blood pool scan is done to:

Check the size of the heart chambers (ventricles).

Check the pumping action of the lower ventricles.

Look for an abnormality in the wall of the ventricles, such as an aneurysm.

Look for abnormal movement of blood between the heart chambers.


A cardiac blood pool scan shows how well your heart is pumping blood to the rest of your body.

Complete test results are usually available in 1 to 2 days. The most commonly reported value is the ejection fraction, which is the average amount of blood pumped out of the heart’s left ventricle during each contraction.

Cardiac blood pool scan
Normal: The ejection fraction is 55% to 65%.
The walls of the ventricles are contracting normally.
The chambers of the heart are not enlarged.
Abnormal: The ejection fraction is less than 55%.
Parts of the heart muscle are not contracting normally.
A defect, such as an aneurysm, is present in the wall of the heart.
The heart valves do not close completely, allowing blood to flow in the wrong direction.
There are openings between the heart chambers, allowing blood to leak between the right and left heart chambers.
The chambers may be enlarged (cardiomyopathy).

Carotid Doppler

Carotid Doppler

Carotid ultrasound is a safe, painless procedure that uses sound waves to examine the structure and function of the carotid arteries in the neck.

You have two carotid (kuh-ROT-id) arteries, one on each side of the neck, which deliver blood from the heart to the brain. Carotid ultrasound can reveal whether an artery has any blockage and how well blood flows through the artery.

Carotid ultrasound is usually used to screen for blockages that indicate an increased risk of stroke. Results from a carotid ultrasound can help your doctor determine what kind of treatment you may need to lower your risk.

Why it’s done

The primary purpose of a carotid ultrasound is to screen for a narrowing of the carotid arteries that indicates an increased risk of stroke. Narrowing is usually caused by plaques — a buildup of fats, cholesterol, calcium and other substances that circulate in the bloodstream. Early detection of narrowing of the carotid arteries enables your doctor to begin treatments that improve blood flow to the brain and decrease your risk of stroke.

Your doctor may recommend a carotid ultrasound if you have medical conditions that increase the risk of stroke. These conditions include:

  • High blood pressure
  • Diabetes
  • High cholesterol
  • Family history of stroke or heart disease

A carotid ultrasound to screen for stroke risk may be used in combination with other tests, including:

Abdominal ultrasound to screen for potential abdominal aortic aneurysm, an enlargement or ballooning of the large artery that supplies blood to the abdomen, pelvis and legs

Ankle-brachial index test, a comparison of your blood pressure measured at an ankle and your blood pressure measured at an arm, which can indicate blockage of blood flow to the legs

Other uses of carotid ultrasound

Your doctor also may order a carotid ultrasound to:

Evaluate the structure and function of the artery after surgery to remove plaques (carotid endarterectomy)

Evaluate the placement and treatment effect of a stent, a mesh tube used to improve blood flow through an artery and support a weakened artery

Locate a collection of clotted blood (hematoma) that may inhibit blood flow

Detect other abnormalities in the structure of a carotid artery that may disrupt blood flow


A doctor who specializes in the reading of imaging tests (radiologist) will review and interpret the results of your carotid ultrasound. He or she will prepare a report for the doctor who ordered the exam, such as your primary care doctor, a specialist in heart and blood vessel disorders (cardiologist), or a specialist in brain and nervous system disorders (neurologist).

The radiologist may also discuss the results of the test with you immediately after the procedure.

The doctor who ordered the test will explain to you what the carotid ultrasound revealed and how the results affect your medical care. If the test was ordered to screen for stroke risk, your doctor may recommend the following treatments, depending on the severity of blockage:

  • Changes in your diet and exercise routine
  • Medication to lower blood cholesterol
  • Medication to prevent blood clots
  • Surgical procedure to remove carotid artery plaques (carotid endarterectomy)
  • Surgical procedure to open up and support your carotid arteries (carotid angioplasty and stenting)

If the test was ordered as a follow-up to a surgical procedure, your doctor can explain whether the treatment is working as planned and whether you’ll require additional treatment or follow-up exams.

Additional Tests

If the results of the carotid ultrasound are unclear, your doctor may order additional imaging tests:

  • Computerized tomography (CT),a specialized X-ray technology that produces thin cross-sectional images of soft tissues
  • Magnetic resonance imaging,which uses a magnetic field and radio waves to produce cross-sectional or 3-D images of soft tissues

Chest X-Ray

Chest X-Ray

Chest X-rays produce images of your heart, lungs, blood vessels, ribs and the bones of your spine. If you go to your doctor or the emergency room with chest pain or shortness of breath, chest X-rays can help determine whether you have heart failure, a collapsed lung, pneumonia, broken ribs or air accumulating in the space surrounding a lung (pneumothorax).

Chest X-rays can also reveal fluid in your lungs or in the spaces surrounding your lungs, enlargement of your heart, pneumonia, emphysema, cancer and many other conditions. Some people have a series of chest X-rays done over time, to track whether a particular health problem is getting better or worse.

In the past, the X-ray was printed out on film. Now, almost all chest X-rays are digital files that are viewed and stored electronically.

Chest X-rays are the most commonly performed radiographic exam. A chest X-ray is often among the first procedures you’ll undergo if your doctor suspects you have heart or lung disease.

A chest X-ray can show:

  • The condition of your lungs
    Chest X-rays can detect cancer or infection in the lungs. They can also show chronic lung conditions, such as emphysema or cystic fibrosis, as well as complications related to these conditions.
  • Heart-related lung problems
    Chest X-rays can reveal changes or abnormalities in your lungs that stem from heart problems. Fluid may accumulate in your lungs (pulmonary edema), for instance, as a result of congestive heart failure.
  • The size and outline of your heart
    Changes in the size and shape of your heart may indicate a variety of conditions, such as heart failure, congenital heart disease, fluid around the heart (pericardial effusion), and problems with one or more of your heart valves.
  • Blood vessels
    Because the outlines of the large vessels near your heart — the aorta and pulmonary arteries and veins — are visible on X-rays, they may reveal aortic aneurysms or other blood vessel problems, or congenital heart disease.
  • Calcium deposits
    Chest X-rays can detect the presence of calcium in your heart or blood vessels. Its presence may indicate damage to your heart valves, coronary arteries, heart muscle or the protective sac that surrounds the heart. Calcium deposits in your lungs may be from an old, resolved infection or a more serious disease.
  • Postoperative changes
    Chest X-rays are useful after you’ve had surgery in your chest, such as on your heart, lungs or esophagus, to monitor your recovery. Your doctor can look at any lines or tubes that were placed during surgery and can make sure there aren’t any air leaks or areas of fluid accumulation.
  • A pacemaker, defibrillator or catheter
    Pacemakers and defibrillators have leads attached to your heart to make sure your heart rate and rhythm are normal, and catheters are small tubes used to deliver medications or for dialysis. A chest X-ray usually is taken after placement of such medical devices to make sure everything is positioned correctly.

You may be concerned about radiation exposure from chest X-rays, especially if you have them regularly. However, the amount of radiation from a chest X-ray is low — even lower than what you’re exposed to through natural sources of radiation in the environment.

The X-ray technologists and radiologists use the smallest possible dose of radiation and provide a protective lead apron when multiple X-rays are necessary.

Women should always inform their physician or X-ray technologist if there is any possibility that they are pregnant. Although you should generally avoid X-rays during pregnancy, a lead apron that covers your pelvis and abdomen can minimize radiation exposure to the baby.

Before the chest X-ray, you generally undress from the waist up and wear an exam gown. Remove jewelry from the waist up, too, since both clothing and jewelry can obscure the X-ray images.

During the procedure, your body is positioned between the X-ray camera and the X-ray digital recorder. You may be asked to move into different positions or angles in order to take views from both the front and the sides of your chest.

During the front view, you stand against the plate that contains the X-ray film or digital recorder. You hold your arms up or to the sides and roll your shoulders forward. You take a deep breath and hold it for several seconds while the X-ray image is taken. Holding your breath after inhaling helps your heart and lungs show up more clearly on the image.

During the side views, you turn and place one shoulder on the plate and raise your hands over your head. Again, you take a deep breath and hold it during the filming process.

Having X-rays taken is generally painless. You don’t feel any sensation as the X-ray passes through your body. If you have trouble standing, you may be able to have X-rays while seated or lying down.

X-rays penetrate body structures and tissue in different ways. Bone is very dense and blocks much of the radiation, so the image of bone on the film appears white. Your heart also blocks some of the radiation and so appears as a lighter area on the film. Lungs are filled with air, so they block little of the radiation, creating a dark image.

A radiologist — a doctor trained in interpretation of X-rays and other imaging exams — analyzes the images, looking for clues that may suggest if you have heart failure, fluid around your heart, cancer, pneumonia or other lung problems, or other conditions.

Your doctor will discuss the results with you as well as what treatments or other tests or procedures may be necessary.

Computed Tomography (CT) Scan of the Body

Computed Tomography (CT) Scan of the Body

A computed tomography (CT) scan uses X-rays to make detailed pictures of structures inside of the body.

During the test, you will lie on a table that is attached to the CT scanner, which is a large doughnut-shaped machine. The CT scanner sends X-rays through the body area being studied. Each rotation of the scanner takes less than a second and provides a picture of a thin slice of the organ or area. All of the pictures are saved as a group on a computer. They also can be printed.

An iodine dye (contrast material) is often used to make structures and organs easier to see on the CT pictures. The dye may be used to check blood flow, find tumors, and look for other problems. The dye can be used in different ways. It may be put in a vein (IV) in your arm, or it may be placed into other parts of your body (such as the rectum or a joint) to see those areas better. For some types of CT scans you drink the dye. CT pictures may be taken before and after the dye is used.

CT scan can be used to study all parts of your body, such as the chest, belly, pelvis, or an arm or leg. It can take pictures of body organs, such as the liverpancreasintestineskidneys,bladderadrenal glandslungs, and heart. It also can study blood vessels, bones, and the spinal cord.

Fluoroscopy CT is a special test that is not widely available. It uses a steady beam of X-rays to look at movement within the body. It allows the doctor to see your organs move or to guide a biopsy needle or other instrument into the right place inside your body.

Why It Is Done

CT scans are used to study areas of the body and the arms or legs.

  • Chest (thorax)
    A CT scan of the chest can look for problems with the lungs, heart, esophagus, the major blood vessel (aorta), or the tissues in the center of the chest. Some common chest problems a CT scan may find include infection, lung cancer, apulmonary embolism, and an aneurysm. It also can be used to see if cancer has spread into the chest from another area of the body.
  • Abdomen
    A CT scan of the abdomen can find cystsabscesses, infection, tumors, an aneurysm, enlarged lymph nodes, foreign objects, bleeding in the belly, diverticulitisinflammatory bowel disease, and appendicitis.
  • Urinary tract
    A CT scan of the kidneys, ureters, and bladder is called a CT KUB or CT urogram. This type of scan can find kidney stones, bladder stones, or blockage of the urinary tract. See a picture of a CT of diseased kidneys. A special type of CT scan, called a CT intravenous pyelogram (IVP), uses injected dye (contrast material) to look for kidney stones, blockage, growths, infection, or other diseases of the urinary tract.
  • Liver
    A CT scan can find liver tumors, bleeding from the liver, and liver diseases. A CT scan of the liver can help determine the cause of jaundice.
  • Pancreas
    A CT scan can find a tumor in the pancreas or inflammation of the pancreas (pancreatitis).
  • Gallbladder and bile ducts
    A CT scan can be used to check for blockage of the bile ducts. Gallstones occasionally show up on a CT scan. But other tests, such as ultrasound, usually are used to find problems with the gallbladder and bile ducts.
  • Adrenal glands
    A CT scan can find tumors or enlarged adrenal glands.
  • Spleen
    A CT scan can be used to check for an injury to the spleen or the size of the spleen.
  • Pelvis
    A CT scan can look for problems of organs in the pelvis. For a woman, these include the uterusovaries, and fallopian tubes. For a man, the pelvic organs include theprostate gland and the seminal vesicles.
  • Arm or leg
    A CT scan can look for problems of the arms or legs, including the shoulder, elbow, wrist, hand, hip, knee, ankle, or foot.



An echocardiogram uses sound waves to produce images of your heart. This commonly used test allows your doctor to see how your heart is beating and pumping blood. Your doctor can use the images from an echocardiogram to identify various abnormalities in the heart muscle and valves.

Depending on what information your doctor needs, you may have one of several types of echocardiograms. Each type of echocardiogram has few risks involved.

Your doctor may suggest an echocardiogram if he or she suspects problems with the valves or chambers of your heart or your heart’s ability to pump. An echocardiogram can also be used to detect congenital heart defects in unborn babies.

Depending on what information your doctor needs, you may have one of the following kinds of echocardiograms:

  • Transthoracic echocardiogram. This is a standard, noninvasive echocardiogram. A technician (sonographer) spreads gel on your chest and then presses a device known as a transducer firmly against your skin, aiming an ultrasound beam through your chest to your heart. The transducer records the sound wave echoes your heart produces. A computer converts the echoes into moving images on a monitor. If your lungs or ribs block the view, a small amount of intravenous dye may be used to improve the images.
  • Transesophageal echocardiogram. If it’s difficult to get a clear picture of your heart with a standard echocardiogram, your doctor may recommend a transesophageal echocardiogram. In this procedure, a flexible tube containing a transducer is guided down your throat and into your esophagus, which connects your mouth to your stomach. From there, the transducer can obtain more-detailed images of your heart. Your throat will be numbed, and you’ll have medications to help you relax during a transesophageal echocardiogram.
  • Doppler echocardiogram. When sound waves bounce off blood cells moving through your heart and blood vessels, they change pitch. These changes (Doppler signals) can help your doctor measure the speed and direction of the blood flow in your heart. Doppler techniques are used in most transthoracic and transesophageal echocardiograms, and can check blood flow problems and blood pressures in the arteries of your heart that traditional ultrasound might not detect.
  • Stress echocardiogram. Some heart problems — particularly those involving the coronary arteries that supply blood to your heart muscle — occur only during physical activity. For a stress echocardiogram, ultrasound images of your heart are taken before and immediately after walking on a treadmill or riding a stationary bike. If you’re unable to exercise, you may get an injection of a medication to make your heart work as hard as if you were exercising.

No special preparations are necessary for a standard transthoracic echocardiogram. Your doctor will ask you not to eat for a few hours beforehand if you’re having a transesophageal or stress echocardiogram. If you’ll be walking on a treadmill during a stress echocardiogram, wear comfortable shoes. If you’re having a transesophageal echocardiogram, you won’t be able to drive afterward because of the sedating medication you’ll receive. Be sure to make arrangements to get home before you have your test.

During the Procedure 

An echocardiogram can be done in the doctor’s office or a hospital. After undressing from the waist up, you’ll lie on an examining table or bed. The technician will attach sticky patches (electrodes) to your body to help detect and conduct the electrical currents of your heart.

If you’ll have a transesophageal echocardiogram, your throat will be numbed with a numbing spray or gel. You’ll likely be given a sedative to help you relax.

During the echocardiogram, the technician will dim the lights to better view the image on the monitor. You may hear a pulsing “whoosh” sound, which is the machine recording the blood flowing through your heart.

Most echocardiograms take less than an hour, but the timing may vary depending on your condition. During a transthoracic echocardiogram, you may be asked to breathe in a certain way or to roll onto your left side. Sometimes the transducer must be held very firmly against your chest. This can be uncomfortable — but it helps the technician produce the best images of your heart.

After the Procedure

If your echocardiogram is normal, no further testing may be needed. If the results are concerning, you may be referred to a heart specialist (cardiologist) for more tests. Treatment depends on what’s found during the exam and your specific signs and symptoms. You may need a repeat echocardiogram in several months or other diagnostic tests, such as a cardiac computerized tomography (CT) scan or coronary angiogram.

Your doctor will look for healthy heart valves and chambers, as well as normal heartbeats. Information from the echocardiogram may show:

  • Heart size. Weakened or damaged heart valves, high blood pressure or other diseases can cause the chambers of your heart to enlarge. Your doctor can use an echocardiogram to evaluate the need for treatment or monitor treatment effectiveness.
  • Pumping strength. An echocardiogram can help your doctor determine your heart’s pumping strength. Specific measurements may include the percentage of blood that’s pumped out of a filled ventricle with each heartbeat (ejection fraction) or the volume of blood pumped by the heart in one minute (cardiac output). If your heart isn’t pumping enough blood to meet your body’s needs, heart failure may be a concern.
  • Damage to the heart muscle. During an echocardiogram, your doctor can determine whether all parts of the heart wall are contributing normally to your heart’s pumping activity. Parts that move weakly may have been damaged during a heart attack or be receiving too little oxygen. This may indicate coronary artery disease or various other conditions.
  • Valve problems. An echocardiogram shows how your heart valves move as your heart beats. Your doctor can determine if the valves open wide enough for adequate blood flow or close fully to prevent blood leakage. Abnormal blood flow patterns and conditions such as aortic valve stenosis — when the heart’s aortic valve is narrowed — can be detected as well.
  • Heart defects. Many heart defects can be detected with an echocardiogram, including problems with the heart chambers, abnormal connections between the heart and major blood vessels, and complex heart defects that are present at birth. Echocardiograms can even be used to monitor a baby’s heart development before birth.

Electrocardiogram (ECG or EKG)

Electrocardiogram (ECG or EKG)

An electrocardiogram is used to monitor your heart. Each beat of your heart is triggered by an electrical impulse generated from special cells in the upper right chamber of your heart. An electrocardiogram – also called an ECG or EKG – records these electrical signals as they travel through your heart. Your doctor can use an electrocardiogram to look for patterns among these heartbeats and rhythms to diagnose various heart conditions.

An electrocardiogram is a noninvasive, painless test. The results of your electrocardiogram will likely be reported the same day it’s performed, and your doctor will discuss them with you at your next appointment.

An electrocardiogram is a painless, noninvasive way to diagnose many common types of heart problems. Your doctor may use an electrocardiogram to detect:

  • Irregularities in your heart rhythm (arrhythmias)
  • Heart defects
  • Problems with your heart’s valves
  • Blocked or narrowed arteries in your heart (coronary artery disease)
  • A heart attack, in emergency situations
  • A previous heart attack

An electrocardiogram is a safe procedure. There may be minor discomfort, similar to removing a bandage, when the electrodes taped to your chest to measure your heart’s electrical signals are removed. Rarely, a reaction to the electrodes may cause redness or swelling of the skin.

A stress test, in which an ECG is performed while you exercise or after you take medication that mimics effects of exercise, may cause irregular heartbeats or, rarely, a heart attack. These side effects are caused by the exercise or medication, not the ECG itself.

There isn’t any risk of electrocution during an electrocardiogram. The electrodes placed on your body only record the electrical activity of your heart. They don’t emit electricity.

No special preparations are necessary. However, avoid drinking cold water or exercising immediately before an electrocardiogram. Cold water can produce potentially misleading changes in one of the electrical patterns recorded during the test. Physical activity, such as climbing stairs, may increase your heart rate.

During the Procedure

An electrocardiogram can be done in the doctor’s office or hospital, and is often performed by a technician. After changing into a hospital gown, you’ll lie on an examining table or bed. Electrodes – often 12 to 15 – will be attached to your arms, legs and chest. The electrodes are sticky patches applied with a gel to help detect and conduct the electrical currents of your heart. If you have hair on the parts of your body where the electrodes will be placed, the technician may need to shave the hair so that the electrodes stick properly.

You can breathe normally during the electrocardiogram. Make sure you’re warm and ready to lie still, however. Moving, talking or shivering may distort the test results. A standard ECG takes just a few minutes.

If you have a heartbeat irregularity that tends to come and go, it may not be captured during the few minutes a standard ECG is recording. To work around this problem, your doctor may recommend another type of ECG:

  • Holter monitoring. Also known as an ambulatory ECG monitor, a Holter monitor records your heart rhythms for an entire 24-hour period. Wires from electrodes on your chest go to a battery-operated recording device carried in your pocket or worn on a belt or shoulder strap. While you’re wearing the monitor, you’ll keep a diary of your activities and symptoms. Your doctor will compare the diary with the electrical recordings to try to figure out the cause of your symptoms.
  • Event recorder. If your symptoms don’t occur often, your doctor may suggest wearing an event recorder. This device is similar to a Holter monitor, but it allows you to record your heart rhythm just when the symptoms are happening. You can send the ECG readings to your doctor through your phone line.
  • Stress test. If your heart problems occur most often during exercise, your doctor may ask you to walk on a treadmill or ride a stationary bike during an ECG. This is called a stress test. If you have a medical condition that makes it difficult for you to walk, medication may be injected to mimic the effect of exercise on the heart.

After the Procedure

Usually, your doctor will be able to tell you the results of your ECG the same day it’s performed. If your electrocardiogram is normal, you may not need any other tests. If the results show there’s a problem with your heart, you may need a repeat ECG or other diagnostic tests, such as an echocardiogram. Treatment depends on what’s causing your signs and symptoms.

Your doctor will look for a consistent, even heart rhythm and a heart rate between 50 and 100 beats a minute. Having a faster, slower or irregular heartbeat provides clues about your heart health, including:

  • Heart rate. Normally, heart rate can be measured by checking your pulse. But an ECG may be helpful if your pulse is difficult to feel or too fast or too irregular to count accurately.
  • Heart rhythm. An ECG can help your doctor identify an unusually fast heartbeat (tachycardia), unusually slow heartbeat (bradycardia) or other heart rhythm irregularities (arrhythmias). These conditions may occur when any part of the heart’s electrical system malfunctions. In other cases, medications, such as beta blockers, psychotropic drugs or amphetamines, can trigger arrhythmias.
  • Heart attack. An ECG can often show evidence of a previous heart attack or one that’s in progress. The patterns on the ECG may indicate which part of your heart has been damaged, as well as the extent of the damage.
  • Inadequate blood and oxygen supply to the heart. An ECG done while you’re having symptoms can help your doctor determine whether chest pain is caused by reduced blood flow to the heart muscle, such as with the chest pain of unstable angina.
  • Structural abnormalities. An ECG can provide clues about enlargement of the chambers or walls of the heart, heart defects and other heart problems.

EndoPAT for Endothelial Dysfunction

EndoPAT for Endothelial Dysfunction

The EndoPAT quantifies the endothelium-mediated changes in vascular tone, elicited by a 5-minute occlusion of the brachial artery (using a standard blood pressure cuff). When the cuff is released, the surge of blood flow causes an endothelium-dependent. Flow Mediated Dilatation (FMD). The dilatation, manifested as Reactive Hyperemia, is captured by EndoPAT as an increase in the PAT Signal amplitude. A post-occlusion to pre-occlusion ratio is calculated by the EndoPAT software, providing the EndoPAT index.

Exercise (Stress) Echocardiogram

Exercise (Stress) Echocardiogram

An echocardiogram (also called an echo) is a type of ultrasound test that uses high-pitched sound waves that are sent through a device called a transducer. The device picks up echoes of the sound waves as they bounce off the different parts of your heart. These echoes are turned into moving pictures of your heart that can be seen on a video screen.

The different types of echocardiograms are:

  • Stress echocardiogram. During this test, an echocardiogram is done both before and after your heart is stressed either by having you exercise or by injecting a medicine that makes your heart beat harder and faster. A stress echocardiogram is usually done to find out if you might have decreased blood flow to your heart.

Exercise Stress Test (TMT)

Exercise Stress Test (TMT)

An exercise electrocardiogram (EKG or ECG) is a test that checks for changes in your heart while you exercise. Sometimes EKG abnormalities can be seen only during exercise or while symptoms are present. This test is sometimes called a “stress test” or a “treadmill test.” During an exercise EKG, you may either walk on a motor-driven treadmill or pedal a stationary bicycle.

The heart is a muscular pump made up of four chambers. The two upper chambers are called atria, and the two lower chambers are called ventricles. A natural electrical system causes the heart muscle to contract and pump blood through the heart to the lungs and the rest of the body.

An exercise EKG translates the heart’s electrical activity into line tracings on paper. The spikes and dips in the line tracings are called waves. A resting EKG is always done before an exercise EKG test, and results of the resting EKG are compared to the results of the exercise EKG. A resting EKG may also show a heart problem that would make an exercise EKG unsafe.

Why It Is Done

  • An exercise electrocardiogram is done to:
  • Help find the cause of unexplained chest pain.
  • Help decide on the best treatment for a person with angina.
  • See how well people who have had a heart attack or heart surgery are able to tolerate exercise.
  • Help find the cause of symptoms that occur during exercise or activity, such as dizzinessfainting, or rapid, irregular heartbeats (palpitations).
  • Check for a blockage or narrowing of an artery after a medical procedure, such as angioplasty or coronary artery bypass surgery, especially if the person has chest pain or other symptoms.
  • See how well medicine or other treatment for chest pain or an irregular heartbeat is working.
  • Help you make decisions about starting an exercise program if you have been inactive for a number of years and have an increased chance of having heart disease.

Experts disagree about the use of an exercise EKG to test people who do not have symptoms of heart disease.

Some experts think that anyone older than age 35 who is generally inactive should have an exercise test to screen for “silent” heart disease before starting a vigorous exercise program.  Because heart disease is rare in younger people who do not have symptoms, an exercise EKG may not be accurate. A falsely abnormal result (false-positive) may cause needless worry and further unnecessary testing.

The U.S. Preventive Services Task Force recommends that exercise testing should not be done routinely for people who have a low risk of a heart attack or stroke.


An exercise electrocardiogram (EKG or ECG) is a test that checks for changes in your heart while you exercise. Your doctor may be able to talk to you about your results right after the test. But complete test results may take several days.

Your doctor will look at the pattern of spikes and dips on your electrocardiogram to check the electrical activity in different parts of your heart. The spikes and dips are grouped into different sections that show how your heart is working.

Exercise electrocardiogram (EKG or ECG) results
Normal: You reach your target heart rate (based on your age) and can exercise without chest pain or other symptoms of heart disease.
Your blood pressure increases steadily during exercise.
Your EKG tracings do not show any significant changes. Your heartbeats look normal.
Abnormal: You have chest pain during or right after the test.
You have other symptoms of heart disease, such as dizziness, fainting, or extreme shortness of breath.
Your blood pressure drops or does not rise during exercise.
The EKG tracing does not look normal.
Your heartbeats are too fast, too slow, or very irregular.

Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body. In many cases MRI gives different information about structures in the body than can be seen with an X-rayultrasound, or computed tomography (CT) scanMRI also may show problems that cannot be seen with other imaging methods.

For an MRI test, the area of the body being studied is placed inside a special machine that contains a strong magnet. Pictures from an MRI scan are digital images that can be saved and stored on a computer for more study. The images also can be reviewed remotely, such as in a clinic or an operating room. In some cases, contrast material may be used during the MRI scan to show certain structures more clearly.

Why It Is Done

Magnetic resonance imaging (MRI) is done for many reasons. It is used to find problems such as tumors, bleeding, injury, blood vessel diseases, or infection. MRI also may be done to provide more information about a problem seen on an X-ray, ultrasound scan, or CT scan. Contrast material may be used during MRI to show abnormal tissue more clearly. An MRI scan can be done for the:

  • Head. MRI can look at the brain for tumors, an aneurysm, bleeding in the brain, nerve injury, and other problems, such as damage caused by a stroke. MRI can also find problems of theeyes and optic nerves, and the ears and auditory nerves.
  • Chest. MRI of the chest can look at the heart, the valves, and coronary blood vessels. It can show if the heart or lungs are damaged. MRI of the chest may also be used to look forbreast or lung cancer.
  • Blood vessels. Using MRI to look at blood vessels and the flow of blood through them is called magnetic resonance angiography (MRA). It can find problems of the arteries and veins, such as an aneurysm, a blocked blood vessel, or the torn lining of a blood vessel (dissection). Sometimes contrast material is used to see the blood vessels more clearly.
  • Abdomen and pelvis. MRI can find problems in the organs and structures in the belly, such as the livergallbladderpancreaskidneys, and bladder. It is used to find tumors, bleeding, infection, and blockage. In women, it can look at the uterus and ovaries. In men, it looks at the prostate.
  • Bones and joints. MRI can check for problems of the bones and joints, such as arthritis, problems with the temporomandibular jointbone marrow problems, bone tumorscartilageproblems, torn ligaments or tendons, or infection. MRI may also be used to tell if a bone is broken when X-ray results are not clear. MRI is done more commonly than other tests to check for some bone and joint problems.
  • Spine. MRI can check the discs and nerves of the spine for conditions such as spinal stenosisdisc bulges, and spinal tumors.

magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body.

The radiologist may discuss initial results of the MRI with you right after the test. Complete results are usually ready for your doctor in 1 to 2 days.

An MRI can sometimes find a problem in a tissue or organ even when the size and shape of the tissue or organ looks normal.


The organs, blood vessels, bones, and joints are normal in size, shape, appearance, and location.
No abnormal growths, such as tumors, are present.
No bleeding, abnormal fluid, blockage in the flow of blood, or bulges in the blood vessels (aneurysms) are present.
No signs of inflammation or infection are present.


An organ is too large, too small, damaged, or absent.
Abnormal growths (such as tumors) are present.
Abnormal fluid from a cause such as bleeding or an infection is present. Fluid is found around the lungs or heart. Fluid is found around the liver, bowel, or other organ in the abdomen.
A blood vessel is narrowed or blocked. An aneurysm is present.
Blockage in the gallbladder bile ducts or in the tubes (ureters) that lead out of the kidneys is present.
Damage to jointsligaments, or cartilage is seen. Bones are broken or show infection or disease.
Problems of the nervous system are present, such as multiple sclerosis (MS)dementiaAlzheimer’s disease, or herniated disc



A mammogram is an X-ray test of the breasts (mammary glands) used to screen for breast problems, such as a lump, and whether a lump is fluid-filled (a cyst) or a solid mass.

mammogram is done to help screen for or detect breast cancer. Many small tumors can be seen on a mammogram before they can be felt by a woman or her GYN doctor. Cancer is most easily treated and cured when it is discovered in an early stage. Mammograms do not prevent breast cancer or reduce a woman’s risk of developing cancer. But regular mammograms can reduce a woman’s risk of dying from breast cancer by detecting a cancer when it is more easily treated.

Experts differ in their recommendations about when or how often women should have mammograms.

  • For women between the ages of 40 and 50, the benefits of regular mammograms are not clear. Women should discuss the benefits and harms of mammograms with their doctors. Talk with Dr. Houston to decide when to start and how often to have a mammogram.
    • The U.S. Preventive Services Task Force (USPSTF) recommends that for women younger than 50 years of age, the decision about when to start regular screening with mammograms every 2 years should be an individual one.1 This decision should be based on her situation, her individual risk, and what she prefers.
    • Some organizations recommend women have mammograms every 1 to 2 years, starting at age 40.
  • For women older than age 50, regular mammograms are recommended.
    • The USPSTF recommends routine mammograms every 2 years for women ages 50 to 74.1
    • Some organizations recommend women have yearly mammograms for as long as they are in good health.
  • Women age 75 and older may want to talk to their doctors about whether they need breast cancer screening.

Dr. Houston may recommend testing at a younger age if you have risk factors for breast cancer.
Breast Cancer Screening: When Should I Start Having Mammograms?
A mammogram that appears to detect a cancer, when in fact a cancer is not present (false-positive results), can occur at any age but is more likely to occur in younger women. About 5% to 10% of screening mammograms will require more testing. This may include another mammogram of specific breast tissue or another test, such as an ultrasound. Most of these tests will show no cancer is present.

Why It Is Done

mammogram is done to:

  • Screen for breast cancer in women without symptoms.
  • Detect breast cancer in women with symptoms. Symptoms of breast cancer may include a lump or thickening in the breast, nipple discharge, or dimpling of the skin on one area of the breast.
  • Locate an area of suspicious breast tissue to remove for examination under a microscope (biopsy) when an abnormality is found.

How It Is Done

  • A mammogram is done by a radiology technologist or mammogram technologist. The X-ray pictures (mammograms) are interpreted by a doctor who specializes in evaluating X-rays (radiologist).
  • You will need to remove any jewelry that might interfere with the X-ray picture. You will need to take off your clothes above the waist, and you will be given a cloth or paper gown to use during the test. If you are concerned about an area of your breast, show the technologist so that the area can be noted.
  • You usually stand during a mammogram. One at a time, your breasts will be placed on a flat plate that contains the X-ray film. Another plate is then pressed firmly against your breast to help flatten out the breast tissue. Very firm compression is needed to obtain high-quality pictures. You may be asked to lift your arm. For a few seconds while the X-ray picture is being taken, you will need to hold your breath. Usually at least two pictures are taken of each breast: one from the top and one from the side.
  • You may be in the mammogram clinic for up to an hour. The mammogram itself takes about 10 to 15 minutes. You will be asked to wait (usually about 5 minutes) until the X-rays are developed, in case repeat pictures need to be taken. At St. Thomas West Hospital, X-ray pictures can be viewed immediately on a computer screen (digitally).


A mammogram may appear to detect a cancer even when a cancer is not present (false-positive results). This can occur at any age but is more likely with younger women. False-positive results can lead to emotional distress and unneeded tests and treatments.

Also, a mammogram may detect abnormalities that will not develop into life-threatening cancer. Tests and treatment after this kind of discovery are not needed and can be harmful.

There is always a slight risk of damage to cells or tissue from being exposed to any radiation, including the very low levels of radiation used for this test. But the risk of damage from the X-rays is very low compared with the potential benefits of the test.


A mammogram is an X-ray test of the breasts (mammary glands) that is used to screen for breast problems, such as a lump, and whether a lump is fluid-filled (a cyst) or a solid mass. Mammogram results are usually available within 10 days. It is not uncommon to be asked to return for another test so an additional view of an area in question can be obtained.

In the United States, facilities that perform mammograms send the results directly to your doctor’s office and must send you a copy of the test results (written in language that is easily understood) within 30 days.

Normal: Breast tissue looks normal. No unusual growths, lumps, or other types of abnormal tissue are seen. The glands that produce milk for breast-feeding and the tubes (ducts) through which milk flows appear normal.
Abnormal: An abnormal growth, lump, or other type of tissue may be seen. A cancerous (malignant) or noncancerous (benign) tumor may be seen. One or more fluid-filled pockets (cysts) may be seen.
Bits of calcium (calcifications) may be seen. Tiny calcifications (microcalcifications) often occur in areas where cells are growing very rapidly (such as in a cancerous tumor). Larger calcifications (macrocalcifications) are usually normal and noncancerous in women older than age 50.
Need more information: A specific area needs to be looked at again. This is a very common result for many women and does not mean that the area is abnormal or cancerous.

Most abnormalities found during a mammogram are not breast cancer. But many women who have regular screening mammograms need more tests to investigate any abnormalities found during a mammogram. If an area of your breast tissue appears to be a concern during a mammogram, other tests may be done.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Deodorant, perfume, powders, or ointments applied to the breasts or under the arms before the test. They may interfere with the X-ray pictures.
  • Breast implants or scar tissue from previous breast surgery. This may make a mammogram harder to interpret.

A mammogram is not usually done if you are:

  • Pregnant, because the radiation could damage your developing baby (fetus). If a mammogram is absolutely necessary for diagnosing a problem, a lead apron will be placed over your abdomen to shield your baby from exposure to the X-rays.
  • Breast-feeding, because breasts that contain milk are very difficult to examine.

Micronutrient Testing from SpectraCell Laboratories

Micronutrient Testing from SpectraCell Laboratories

SpectraCell Laboratories, Inc. is a CLIA accredited clinical laboratory that specializes in micronutrient testing. This patented process resulted from 18 years of research at the University of Texas. The micronutrient tests measures how micronutrients are actually functioning within your patients’ white blood cells. These tests allow nutritional assessment of your patients for a broad variety of clinical conditions including arthritis, cancer, cardiovascular risk, diabetes, various immunological disorders, metabolic disorders and micronutrient deficiencies. Also offered by SpectraCell is a specialized profile of homocysteine, lipids and proteins to assess cardiovascular risk.

PET Scan (Positron Emission Tomography)

PET Scan (Positron Emission Tomography)

Positron emission tomography (PET) is a test that uses a special type of camera and a tracer (radioactive chemical) to look at organs in the body. The tracer usually is a substance (such as glucose) that can be used (metabolized) by cells in the body.

During the test, the tracer liquid is put into a vein (intravenous, or IV) in your arm. The tracer moves through your body, where much of it collects in the specific organ or tissue. The tracer gives off tiny positively charged particles (positrons). The camera records the positrons and turns the recording into pictures on a computer.

PET scan pictures do not show as much detail as computed tomography (CT) scans or magnetic resonance imaging (MRI) because the pictures show only the location of the tracer. The PET picture may be matched with those from a CT scan to get more detailed information about where the tracer is located.

A PET scan is often used to evaluate cancer, check blood flow, or see how organs are working.

Why It Is Done
positron emission tomography (PET) scan is done to:

Tanita Body Composition Analyzer

Tanita Body Composition Analyzer

Tanita Body Composition Analyzers help patients to understand what is going on inside their bodies by categorizing weight into muscle mass, water, and body fat. This knowledge can help patients with weight-related problems make better-informed decisions about their behavior. It helps them to see the effectiveness of their treatment program – especially relevant if obesity-related medication is part of the program.

Tanita’s detailed results and accurate reporting will also improve patient compliance, improving health outcomes.

Telomere Testing

Telomere Testing

The ONLY commercially available telomere analysis in the United States.

Telomere Diagram - Shows telomeres at the end of...What does Telomere Testing measure?

Telomeres are sections of genetic material at the end of each chromosome whose primary function is to prevent chromosomal “fraying” when a cell replicates. As a cell ages, its telomeres become shorter. Eventually, the telomeres become too short to allow cell replication, the cell stops dividing and will ultimately die – a normal biological process. SpectraCell’s Telomere Test can determine the length of a patient’s telomeres in relation to the patient’s age.

Telomere Graph Sample - Sample of a Telomere graphHow are the results reported?

The Patient Telomere Score is calculated based on the patient’s telomere length on white blood cells (T-lymphocytes). This is the average compared to telomere length on lymphocytes from a sample of the American population in the same age range. The higher the telomere score, the “younger” the cells. A Telomere Score that is above the average line is desirable.

What do the results mean to the patient and the doctor?

Age adjusted telomere length is the best method to date to assess biological age using structural analysis of chromosomal change in the telomere. Serial evaluation of telomere length is an indicator of how rapidly one ages relative to a normal population. Therapies directed at slowing the loss of telomere length may slow aging and age-related diseases.

Telomeres - Shows telomere endsWhat are the nutritional implications on telomere length and repair?

An inflammatory diet, or one that increases oxidative stress, will shorten telomeres faster. This includes refined carbohydrates, fast foods, processed foods, sodas, artificial sweeteners, trans fats and saturated fats. A diet with a large amount and variety of antioxidants that improves oxidative defense and reduces oxidative stress will slow telomere shortening. Consumption of 10 servings of fresh and relatively uncooked fruits and vegetables, mixed fiber, monounsaturated fats, omega-3 fatty acids, cold water fish, and high quality vegetable proteins will help preserve telomere length. In addition, it is advised to reduce total daily caloric intake and implement an exercise program. Fasting for 12 hours each night at least 4 days per week is recommended.

What lifestyle modifications are likely to be helpful?

One should achieve ideal body weight and body composition with low body fat (less than 22 % for women and less than 16 % for men). Decreasing visceral fat is very important. Regular aerobic and resistance exercise for at least one hour per day, sleeping for at least 8 hours per night, stress reduction, discontinuation of all tobacco products are strongly recommended. Bioidentical hormone replacement therapy may decrease the rate of telomere loss.

When should retesting be considered?

Testing should be done once per year to evaluate the rate of aging and make adjustments in nutrition, nutritional supplements, weight management, exercise and other lifestyle modifications known to influence telomere length.

What role will nutritional supplements play in slowing telomere shortening?

Oxidative stress will shorten telomere length and cause aging in cellular tissue. Antioxidant supplements can potentially reduce oxidative stress very effectively, which will ultimately improve oxidative defenses, mitochondrial function, reduce inflammation and slow vascular aging. Targeted supplementation is key, as antioxidants work synergistically and must be balanced to work most effectively and avoid inducing a pro-oxidant effect. Increasing antioxidant capacity at the cellular level is critical to maintaining telomere length.

Recent evidence suggests that a high quality and balanced multivitamin will also help maintain telomere length. Specifically, studies have linked longer telomeres with levels of vitamin E, vitamin C, vitamin D, omega-3 fatty acids and the antioxidant resveratrol. In addition, homocysteine levels have been inversely associated with telomere length, suggesting that reducing homocysteine levels via folate and vitamin B supplementation may decrease the rate of telomere loss. Similarly, conditions such as cardiovascular disease, insulin resistance, diabetes, hypertension, atherosclerosis and even dementia affect telomere length. Correcting subclinical nutritional deficiencies that may contribute to such diseases is crucial for telomere maintenance.

What pharmacologic treatments are known to slow telomere aging?

  • Angiotensin converting enzyme inhibitors (ACEI)
  • Angiotensin receptor blockers (ARB)
  • Renin Inhibitors
  • Statins
  • Possibly Calcium channel blockers
  • Possibly Serum aldosterone receptor antagonists
  • Possibly metformin
  • Aspirin
  • Bioidentical Hormone Replacement Therapy

Control all known coronary heart disease risk factors to optimal levels

  • Reduce LDL cholesterol to about 70 mg %, decrease
  • LDL particle number and increase LDL particle size.
  • Reduce oxidized LDL.
  • Increase HDL to over 40 mg % in men and over 50 mg % in women and increase HDL 2 subfraction. Reduce inflammatory HDL and increase protective HDL.
  • Reduce fasting blood glucose to less than 90 mg % and 2 hour post prandial or 2 hour GTT to less than 110 mg %. Keep Hemoglobin A1C to about 5.0% and keep insulin levels low.
  • Reduce blood pressure to about 120/ 80 mm Hg
  • Reduce homocysteine to less than 8 um/L
  • Reduce HS-CRP to less than 1.0
  • Maintain ideal body weight and composition.
  • Stop smoking.
  • Treat insulin resistance and metabolic syndrome.

Overall recommendations to maintain telomere length

Some clinicians have recommended reducing all known coronary risk factors, inflammation, oxidative stress, ADMA levels and angiotensin II levels or its action. At the same time, therapy should increase nitric oxide levels and nitric oxide bioavailability, increase arginine, increase endothelial progenitor cells, improve mitochondrial function and increase oxidative defenses. In addition, one should optimize hormone levels, exercise, sleep, nutrition and nutritional supplements. Fasting and caloric restriction should be part of the regimen as well.


Telomeres are sections of genetic material at the end of each chromosome whose primary function is to prevent chromosomal “fraying” when a cell replicates. As a cell ages, its telomeres become shorter. Eventually, the telomeres become too short to allow cell replication, the cell stops dividing and will ultimately die – a normal biological process. SpectraCell’s Telomere Test can determine the length of a patient’s telomeres in relation to the patient’s age.
SpectraCell’s Telomere Test analyzes:

  • Lysis of Cells
  • DNA Extraction
  • Amplification

Telomeres and Aging - Understanding Cellular Aging

Telomeres and Aging – Understanding Cellular Aging

What is a Telomere?

chromosome is a long strand of DNA. At the end of a chromosome is a telomere, which acts like a bookend. Telomeres keep chomosomes protected and prevent them from fusing into rings or binding with other DNA. Telomeres play an important role in cell division.

What Happens When a Cell Divides?

Each time a cell divides, the DNA unwraps and the information in the DNA is copied. The process does not copy all of the DNA information – the telomeres are not copied. When the cell is finished dividing, the DNA comes back together. The telomeres lose a little bit of length each time this happens.

Why Do They Get Shorter?

When a cell divides and copies DNA, the strands of DNA get snipped to enable the copying process. The places that are snipped are the telomeres. Since the telomeres do not contain any important information, more important parts of the DNA are protected. The telomeres get shorter each time a cell divides, like a pencil eraser gets shorter each time it’s used.

Can Telomeres Become Too Short?

Yes. When the telomere becomes too short, essential parts of the DNA can be damaged in the replication process. Scientists have noticed that cells stop replicating when telomeres are shorter. In humans, a cell replicates about 50 times before the telomeres become too short. This limit is called the Hayflick limit (after the scientist who discovered it).

How Does All This Affect Aging?

Researchers can use the length of a cell’s telomeres to determine the cell’s age and how many more times is will replicate. This is important in anti-aging research. When a cell stops replicating, it enters into a period of decline known as “cell senescence,” which is the cellular equivalent of aging. However, another reason telomeres are important is cancer.

Cancer? Why Are We Talking About Cancer Now?

Cancer is a condition in which certain cells in your body stop dying. Every system in your body is carefully balanced to allow for cells replicating and dying. If cells stop dying and keep replicating, the balance is disrupted and there are too many of one kind of cell. Groups of these cells form tumors. Researchers believe that cancer cells are creating an enzyme called telomerase, which prevents telomere shortening.

Where Does Telomerase Come From?

Every cell in your body has the genetic code to make telomerase, but only certain cells need to produce this enzyme. White blood cells and sperm cells, for example, need to have telomere shortening switched off in order to make more than 50 copies of themselves through your lifetime. In advanced cancer, the cancer cells also seem to be producing telomerase, which allows them to continue to replicate without dying.