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 congestive heart failure. One of several techniques may be used.
Myocardial perfusion imaging is obtained by injection of a small dose of technisium, 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 cardiac 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. If you are unable to exercise, medications can be used to generate the same effect.