- Exercise Stress Tests
- Exercise Stress Echocardiograms
- Nuclear Stress Tests
- Carotid Ultrasounds
- Peripheral Vascular Studies
- T-Wave Alternans
- Holter Monitoring
- Telephone Pacer Evaluations
Exercise Stress Tests
Cardiac stress testing can be useful in identifying partial blockages in your coronary arteries.
Many times, the presence of coronary artery disease (CAD) is easily missed when a person is at rest, because at rest there may be no sign of a problem either on physical examination or on the ECG. In these cases, cardiac abnormalities may become apparent only when the heart is asked to perform at increased workloads.
The stress test is used to evaluate the heart and vascular system during exercise. It helps answer to two general questions: 1) Is CAD present that only becomes apparent when the heart is stressed by exercise? 2) If there is underlying heart disease, how severe is it likely to be?
How is a stress test performed?
First, you will have leads (wires) to an ECG machine attached to your chest, and a blood pressure cuff is placed on your arm. A clothespin-like sensor may be placed on your finger to measure the amount of oxygen in your blood. After a baseline ECG is obtained, you will be asked to begin performing a low level of exercise, either by walking on a treadmill, or pedaling a stationary bicycle. The exercise is "graded" - that is, every three minutes, the level of exercise is increased. At each "stage" of exercise, your pulse, blood pressure and ECG are recorded, along with any symptoms you may be experiencing.
With a "maximal" stress test, the level of exercise is gradually increased until you cannot keep up any longer because of fatigue, or until your symptoms (chest pain, shortness of breath, or lightheadedness) prevent further exercise, or until changes on your ECG indicate a cardiac problem. Maximal stress tests should be performed when the goal is to diagnose the presence or absence of CAD.
With a "submaximal" stress test, you will exercise only until a pre-determined level of exercise is attained. Submaximal tests are used in patients with known CAD, in order to measure whether a specific level of exercise can be performed safely.
After the test, you will be monitored until any symptoms disappear, and until your pulse, blood pressure and ECG return to baseline.
What kinds of heart disease can the stress test help to evaluate?
The stress test is useful chiefly in the diagnosis of CAD that is producing blockages in the coronary arteries, the arteries that supply blood to the heart muscle. If a partial blockage is present, the heart muscle supplied by that partial blockage may be getting all the blood it needs in the resting state. But if the person with this partial blockage exercises, the artery may not be able to supply all the blood the heart muscle needs to perform at the high level now needed. When a portion of the heart muscle is suddenly not receiving enough blood flow, it becomes oxygen-starved, or ischemic. Ischemic heart muscle often causes chest discomfort (a symptom called "angina") and characteristic changes on the ECG. It can also cause changes in the heart rhythm, or in the blood pressure. By "stressing" the heart with exercise, the stress test can bring out abnormalities caused by partial blockages in the coronary arteries - abnormalities that are often completely unapparent at rest.
It is important to note that the stress test can only help to diagnose CAD that is producing partial blockages - so-called obstructive CAD. CAD often produces plaques in the arteries that are not actually causing obstruction, and these non-obstructive plaques can (and do) rupture, causing acute blood clot formation, which produces an acute obstruction of the artery, often leading to myocardial infarction (heart attack). So it is certainly possible to have a "normal" stress test while still having CAD.
Because exercise raises adrenaline levels, stress tests can also be useful in diagnosing certain cardiac arrhythmias that tend to occur at times when adrenaline levels are increased.
Stress tests are also useful in measuring the "functional capacity" of patients with heart disease. If a patient has CAD, for instance, the stress test can help assess the significance of partial blockages. If signs of ischemia occur at a low level of exercise, the blockages are likely to be very significant. But if ischemia does not occur, or if it occurs only at very high levels of exercise, the blockages are likely to be much less significant.
Performing periodic stress tests can also be a useful way of monitoring the progress of patients with congestive heart failure. If the peak level of attainable exercise is worsening over time, either the underlying heart disease may be worsening, or the patient's medical therapy may need to be re-adjusted.
What are the limitations of the stress test?
In some patients, ECG changes suggestive of ischemia can occur even in the absence of CAD. (In other words, "false positive" stress tests are not uncommon.) In other patients, no significant ECG changes are seen even in the presence of CAD. (So "false negative" stress tests can be seen.) False positive and false negative studies can significantly limit the usefulness of the stress test in many patients. By adding a nuclear perfusion study to the stress test, this limitation is minimized, and the diagnostic capacity of the stress test is greatly improved.
What are the risks of having a stress test?
The stress test has proven to be remarkably safe. It poses about the same level of risk as taking a brisk walk or walking up a hill. While it is possible that the ischemia provoked by such stress can lead to a myocardial infarction or to serious heart rhythm disturbances, in practice this event is rare. Further, when these serious events do occur during a stress test, they occur in the presence of trained medical personnel who can deal with them immediately.
The echocardiogram is an extremely useful test for studying the heart's anatomy. It is non-invasive and entirely safe, and when interpreted by well-trained cardiologists, is very accurate.
How is the echocardiogram performed?
The echocardiogram is a simple test to have done. You will lie on an examination table, and a technician will hold a transducer (a device that resembles a computer mouse) against your chest, slowly sliding it back and forth. (The technician will apply a Vaseline-like gel to your chest to aid in sliding the transducer.) You may be asked to roll on your side during the test, or hold your breath for a few seconds. The test takes 30 to 60 minutes to complete.
How does the echocardiogram work?
The transducer that's placed on your chest sends sound waves toward the heart. Like the sonar on a submarine, the sound waves bounce off the heart, and are collected by by the transducer.
These returning sound waves are processed by a computer, assembled into a two-dimensional image of the beating heart, and displayed on a TV screen (which you will be able to see if you wish). By aiming the transducer, the technician will be able to image most of the important cardiac structures.
What is the echocardiogram good for?
The echocardiogram reveals important information about the anatomy of the heart. It is especially useful for detecting problems with the heart valves (such as aortic stenosis or mitral valve prolapse). It is also an extremely useful test for evaluating congenital heart disease. The echocardiogram is also a good way to get a general idea of the overall function of the heart muscle.
What is the echocardiogram not good for?
The echo does not image the coronary arteries, and is not useful for detecting coronary artery disease. It is not as accurate as the MUGA scan for measuring overall cardiac muscle function. Various physical variations (a thick chest wall, for instance, or emphysema) may limit the ability to image cardiac structures. These physical variations, however, can be overcome by performing a trans-esophageal echo test.
Exercise Stress Echocardiograms
Echocardiograms are sometimes used in conjunction with stress tests. An echo test is made at rest, and then is repeated during exercise, to look for changes in the function of the heart muscle when exercise is performed. Deterioration in muscle function during exercise can indicate coronary artery disease.
For more information on this test please read about the two components separately above: Exercise Stress Test (Link) and Echocardiogram (Link)
Digirad provides equipment, staffing, quality control, nuclear licensing and radiopharmaceuticals to allow patients to be imaged in the comfort and convenience of our office under Dr.Terzian's direct supervision.www.digirad.com
The Cardiolite scans (Cardiolite is the trade name for sestamibi) are tests that show how well blood is flowing to various portions of the heart muscle. These tests, so-called "nuclear perfusion studies," are generally used in conjunction with stress tests to non-invasively detect the presence of coronary artery disease (CAD) that is producing partial obstructions in the coronary arteries.
What is Cardiolite?
Cardiolite is a radioactive substance. When injected into the bloodstream, this substance collects in the portions of heart muscle that have good blood flow. If one of the coronary arteries (the arteries that supply blood to the heart muscle) is blocked or partially blocked, relatively little Cardiolite accumulates in the muscle supplied by that blocked artery.
How are nuclear perfusion studies performed?
During your stress test, Cardiolite will be injected into your vein when you have attained your maximum level of exercise. The radioactive substance will distribute itself throughout your heart muscle in proportion to the blood flow received by that muscle. Cardiac muscle receiving normal blood flow accumulates a larger amount of Cardiolite than cardiac muscle that is supplied by diseased coronary arteries.
An image of your heart will then be made by a special camera that can "see" the Cardiolite. From these pictures, any portions of the heart that are not receiving normal blood flow (because of blockage in the coronary arteries) can be identified.
What are nuclear perfusion studies good for?
Using Cardiolite perfusion imaging greatly increases the accuracy of the stress test in diagnosing obstructive CAD. A normal Cardiolite test is an excellent indication that you have no significant blockages in your coronary arteries. On the other hand, patients with abnormal perfusion scans are highly likely to have significant blockages.
What are the risks of nuclear perfusion scans?
These noninvasive studies are very safe. Their only drawback is that radiation is used. The level of radiation the patient receives is felt to produce only a very small risk of harm, and for appropriately selected patients the potential for benefit far outweighs this small risk.
Carotid Duplex Ultrasound
Ultrasound involves the use of high-frequency sound waves to create images of organs and systems within the body. A Carotid duplex is an ultrasound test that shows how well blood is flowing through the carotid arteries. The carotid arteries are located in the neck. They supply blood to the brain.
How the Test is Performed?
The test is done in a vascular lab. You will be asked to lie on your back. Your head will be supported to prevent it from moving. The health care provider applies a water-soluble gel on your skin and gently runs a handheld device called a transducer over the area of the carotid arteries in your neck. The device sends high-frequency sound waves to the arteries in your neck. The sound waves bounce off the blood vessels and form images or pictures of the insides of the arteries.
How to Prepare for the Test?
No preparation is necessary.
How the Test Will Feel?
You may feel some pressure as the probe is moved around your neck. The pressure should not cause any pain. You may also hear a "whooshing" sound.
Why the Test is Performed
The carotid duplex test checks blood flow in the carotid arteries. It can detect:
- Blood clotting (thrombosis)
- Narrowing in the arteries (stenosis)
- Other causes of blockage in the carotid arteries
Your doctor may order this test if:
- You have had a stroke or transient ischemic attack (TIA)
- You need a follow-up test because: The carotid artery was found to be narrowed in the past
- You have had surgery on your carotid artery
- Your doctor hears an abnormal sound called a bruit over the carotid neck arteries. This may mean the artery is narrowed.
The results will tell your doctor how open or narrowed your carotid arteries are. For example, the arteries may be 10% narrowed, 50% narrowed, or 75% narrowed.
A normal result means there is no problem with the blood flow in the carotid arteries. The artery is free of any blockage, narrowing, or other problem.
Note: Value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
An abnormal result means the artery may be narrowed, or something is changing the blood flow in the carotid arteries. This is a sign of atherosclerosis or blood vessel conditions. In general, the more narrowed the artery is, the higher your risk for stroke. Depending on the results, your doctor may want you to:
- Consider surgery
- Have additional tests (such as cerebral angiography, CT angiography, and magnetic resonance angiography)
- Follow a healthy diet and lifestyle to prevent atherosclerosis
- Repeat the test again in the future
See the article on atherosclerosis for further treatment information.
There are no specific risks related to having this procedure.
Microvolt T-Wave Alternans Test
Microvolt T-Wave Alternans is a non-invasive test that can help identify patients at risk for Sudden Cardiac Arrest. T-wave Alternans (TWA) refers to an alternating pattern in the T-wave portion of the surface electrocardiogram (ECG). This test is able to detect subtle, microvolt-level T-wave alternans not visible to the human eye and can be used to detect subtle changes in the ECG.
How a Microvolt T-Wave Alternans Test is performed?
Patients typically walk on a treadmill for several minutes with a set of 14 electrodes on the torso: seven standard (the same used in a conventional stress test) and seven Micro-V Alternans Sensors. Unlike stress testing, the heart rate is increased gradually and patients are not required to exercise until exhaustion.
For more information visit: http://www.cambridgeheart.com/mtwa/mtwa