During a traditional stress test, the heart’s electrical activity is measured by electrocardiograms (EKGs) both at rest and under exertion.

A nuclear stress test is a noninvasive test that combines exercise with a form of nuclear imaging such as a SPECT scan or PET scan. In either case, the test can reveal more detailed information than a conventional exercise EKG test.

During a SPECT exercise test, a patient is injected with an isotope, usually thallium but sometimes a technetium labeled agent such as sestamibi or tetrofosmin, to take pictures of the heart muscle. The isotope is absorbed by the heart muscle (myocardium), allowing physicians to use a special camera to obtain images of the heart. By studying the distribution of the isotope into the heart muscle, physicians can gauge the health of the heart and adequacy of coronary blood supply at rest and under stress.

A nuclear stress test can help measure:

A nuclear stress test is not appropriate for everyone. Patients who may not be candidates for this test include those with the following conditions:

• Inflammation of the heart muscle (myocarditis)
  
  
• Recent pulmonary (lung) infection
  
  
• Coarctation of the aorta
  
  
• Pregnancy
  
  
• Severe narrowing (stenosis) of the aortic valve
  
  
• Severe heart failure

Cardiac PET scans, another type of radionuclide imaging test, can determine the presence and extent of coronary artery disease. It is an excellent tool for determining whether portions of the heart muscle are still viable (living and functioning). It is also very accurate, and it has shown it to be more sensitive than thallium stress testing. Studies have found that thallium stress testing may overestimate the extent of heart damage by as much as 30 percent of the time. PET scans may be recommended when other non-invasive tests (e.g., echocardiogram) do not yield a definite diagnosis.