Stress Testing

The exercise ECG test (treadmill) allows doctors to study changes in the ECG when the heart is made to work harder. The patient walks on a treadmill while the ECG is being recorded. The test not only measures exercise tolerance objectively, but also is designed to elicit symptoms, arrhythmias, or electrocardiographic changes that are brought on by exercise. The test is valuable in the diagnosis and assessment of severity of known or suspected coronary artery occlusive disease (CAD). It is also used in selected asymptomatic patients to screen for possible CAD. The test is also valuable in assessing the patient after recovery from a heart attack. In patients with known CAD on medication or who have undergone balloon angioplasty or coronary bypass surgery treatment, exercise ECG testing may be used to assess the effectiveness of therapy.

Exercise stress tests are helpful in assessing the risk or likelihood that a patient has significant coronary artery blockages. A more sensitive test that is used in many patients in the Stress Exercise Myocardial Perfusion Imaging Test. The treadmill stress test is performed in conjunction with acquisition of thallium or technetium Sestamibi (MIBI) images. Thallium and technitium are low level and safe radioactive nuclear imaging agents ("tracers") that are taken up by the heart muscle and allow images to be made of the muscle. If circulation to the heart is abnormal, the radioactive material is not available to the muscle and a defect in the image is noted. Two sets of images are acquired: one set at rest and one set with exercise. If a defect is noted in the resting images, either no blood flow is available to that region of the heart or no viable tissue is present to take up the tracer and display the signal. Comparison of the rest and exercise images allows very sensitive assessment of the adequacy blood flow to the heart muscle tissue. This blood flow assessment can be highly predictive of significant coronary artery blockages as well as indicating previous complete blockages and permanent damage to the heart. The radioactive isotope injected for the study produces less radiation than x-ray procedures such as a CAT scan or kidney study and is non-allergenic.

Myocardial perfusion imaging is indicated in some patients who are unable to perform treadmill exercise because of orthopedic problems or who have certain electrical abnormalities with their heart making normal stress studies less reliable. In such patients, the cardiac effect of exercise stress can be simulated by the intravenous administration of a coronary vasodilator such as adenosine or a cardiac stimulant such as dobutamine. Since caffeine alters the efficacy of the test, it is essential that no coffee, tea or caffeine containing beverages or medications be consumed for 24 hours prior to the test.