TESTS: CARDIAC STRESS TESTING

Cardiac stress testing involves procedures that measure and compare heart function at rest and during exercise. Faster heart rates make it easier to detect impaired blood flow to the heart or abnormal heart rhythms. Cardiac stress testing is performed to diagnose a heart condition, monitor progress in those who have had a heart attack or have undergone heart surgery, and determine safe exercise levels for people who have heart disease or are at risk for developing it. Cardiac stress testing is safe, quick and noninvasive.

Stress ECG

The stress ECG is a variation of the standard electrocardiogram, which measures the electrical activity of the heart while at rest. In the stress ECG, 12 electrodes are attached to the upper body, arms and legs, and an electrocardiogram is taken. Blood pressure is also monitored continuously. Next, heart rate is raised as the person exercises on a treadmill or a stationary bicycle. The level of exertion is increased gradually by raising the slope or speed of the treadmill or the resistance of the bicycle pedals. The test continues until the heart rate hits a predetermined upper limit or until the person being tested can no longer continue because of fatigue, angina (chest pain), or breathlessness. ECGs are taken throughout the exertion and during the 10- or 15-minute period afterward, at which time the person cools down and recovers from the exertion. Changes in heart function before, during, and after exertion can reveal underlying heart disease and allow a doctor to assess its type and severity.

Pharmacological Stress Test

Also known as the chemical stress test, this method is used for those who cannot perform a physical activity like walking on a treadmill or riding a bicycle. The person to be tested is injected with a drug such as dobutamine or adenosine, which causes the heart rate to speed up even though the person is actually resting. An ECG is administered before the drug is given and then again after the drug takes effect. This information allows diagnosis and assessment of the function of the heart, much like a standard stress ECG.

Stress Echocardiogram

In echocardiography, a small device called a transducer, which emits ultrasound waves and captures the returning echoes, is placed against the chest. A machine then turns the echoes into an image of the heart. Echocardiography allows doctors to visualize the heart as it is moving and to observe its main pumping chambers, the shape and thickness of the chamber walls, the valves, and the outer covering and major vessels of the heart. It is also possible to determine the volume and direction of blood flow through the heart. For a stress echocardiogram, echocardiography is performed before, during, and after exertion on a treadmill or bicycle. The echocardiogram can then detect changes in the motion of the heart muscle after exercise, suggesting underlying heart disease.

Nuclear Stress Test

This type of cardiac stress testing is valuable for determining which parts of the heart muscle have good blood flow and which do not. The person is injected with an extremely small amount of a radionuclide (radioactive substance), usually thallium. The thallium, which travels through the bloodstream, can be detected by a gamma camera. Areas of the heart with good blood supply appear dark on the gamma camera because of the presence of the thallium, while areas with reduced or absent blood flow appear gray or white. By taking gamma camera pictures of the heart before, during, and after exercise, doctors can determine whether areas of heart muscle have been damaged and whether normal blood flow is blocked or obstructed. A nuclear stress test is safe because the amount of radioactivity is minuscule and because the thallium loses its radioactivity in a matter of hours.

Excerpted from: Complete Medical Encyclopedia, American Medical Association, 2003.

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