Nuclear imaging techniques are usually reserved for patients whose EKG findings are difficult to interpret or for patients with a normal EKG whose history is highly suspicious for coronary artery disease. One of several techniques may be used.

Thallium scintigraphy is obtained by injection of a small dose of thallium, a harmless radioactive isotope, into the bloodstream. A nuclear camera and computer compile images of the heart based on patterns of concentration of the isotope in the heart muscle tissue. The resting scan offers doctors a non-invasive method to identify the location and extent of damage to heart tissue from a heart attack. Combined with exercise, the scans can be used to evaluate the heart's ability to recover from an ischemic episode.

For the exercise scan, another injection of the isotope is given at peak exercise to record images of the heart muscle during increased work. Areas of the heart not receiving enough blood show up as “perfusion” or blood flow defects. Additional images may be obtained three to four hours later to see if any perfusion defects seen at peak exercise have disappeared or are reduced in size. The technique is also used to detect cardiomyopathies, such as abnormal enlargement of a heart chamber.

Radionuclide angiography is another method of nuclear imaging used for heart evaluations. It involves a different radioactive isotope — technetium — to provide a computerized image of the sequence of movements in an average cardiac cycle. In this test, the patient lies down on an exercise table fitted with bicycle pedals to progressively increase the demands on the heart. Images obtained with a nuclear camera are used to evaluate the size, shape and function of the left ventricle, as well as to detect abnormalities in the movement of the heart muscle walls. Aneurysms, or a ballooning of tissue on the heart wall, can also be detected with this technique. With the advent of thallium studies, radionuclide angiography has been used with decreasing frequency.