Role of nuclear cardiac imaging in myocardial infarction: postinfarction risk stratification.

Over the past two decades, advancements in nuclear cardiac imaging have greatly improved the overall evaluation of patients surviving acute myocardial infarction (AMI). Initially used only to detect the presence of AMI in patients with an unclear clinical diagnosis, nuclear cardiac imaging has matured into a technique that can now accurately assess individual patient risk among seemingly stable survivors of AMI based on the total left ventricular (LV) perfusion defect size (PDS), the extent of inducible ischemia, and the degree of LV dysfunction. Gated radionuclide angiography (RNA) and first-pass RNA were first used to assess LV ejection fraction (EF) and LV volumes—both strong independent predictors of survival. However, the development of technetium 99m– based perfusion agents enabled assessment of LV function by direct gating of the perfusion images. With the transition from planar to single photon emission computed tomography (SPECT) perfusion imaging, further refinements in risk stratification became possible. The introduction of quantitative SPECT analysis added a new dimension to risk stratification by affording an accurate estimate of the stress-induced LV PDS and the extent of scintigraphic ischemia. With advances in AMI therapeutics and the need for earlier risk assessment, pharmacologic vasodilators were developed as an alternative to treadmill exercise stress. Both adenosine and dipyridamole can be administered safely even within the first few days of AMI, allowing very early risk stratification based on the gated SPECT perfusion and functional results and thereby expediting appropriate patient care. Recent studies indicate that gated SPECT imaging may be used not only to assess initial patient risk but also to track subsequent risk based on the therapeutic effects of