a n d Rory H a c h a m o v i t c h , M D
As a tool for examining patients with coronary artery disease (CAD), myocardial perfusion single photon emission computed tomography is increasingly finding its greatest value in risk assessment rather than in pure diagnosis of CAD. With greater prognostic accuracy, better-informed decisions about how to maximize therapeutic benefits become possible.
Several significant factors help to determine prognosis in CAD. They are (1) the amount of infarcted myocardium; (2) the amount of jeopardized myocardium supplied by vessels with significant stenoses, (3) the degree of jeopardy, which is related to the degree of coronary stenosis; and (4) the stability or instability of the coronary lesions. The first three factors can be well evaluated by nuclear methods, which assess perfusion, function, or their combination. Nuclear techniques currently do not directly contribute information to the fourth factor, although this factor has prompted much recent investigation.
Incremental Pro~ao~ยข Information
Because nuclear tests are not inexpensive, for their application to be cost effective the data obtained from these tests should contribute incremental information that cannot be derived from the patient's clinical history and risk factors, standard electrocardiography (ECG) findings, or exercise ECG findings.
The concept of incremental information can be applied to diagnostic or to prognostic end points, but the critical probability levels for clinical decision making differ significantly in these two approaches. Diagnostic testing is usually applied to patients with immediate likelihood of disease; typically a probability of 80% to 90% or greater is considered a high probability for