Sensitivity, specificity, and prognostic significance of noninvasive testing for occult or known coronary disease.

T HE DEVELOPMENT of radionuclide techniques performed in conjunction with exercise stress testing for the assessment of myocardial perfusion and global and regional cardiac dynamics in the past decade has provided the clinical cardiologist with noninvasive approaches for detecting occult coronary artery disease (CAD) and determining both the extent and severity of functionally significant coronary narrowings. Information derived from cardiac radionuclide imaging is different from anatomic information obtained from coronary arteriography. Coronary angiography is presently the "gold standard" for establishing the diagnosis of CAD in patients with chest pain and documenting its extent by the delineation of focal coronary obstructions that are considered significant (eg >_50% stenosis). However, the angiographic evaluation of the epicardial segments of the three major coronary arteries cannot provide data relevant to the amount of myocardium that is rendered ischemic under such stress conditions as exercise, dipyridamole-induced vasodilation, and cold pressor stimulation. Some studies have shown interobserver variability in the interpretation of coronary arteriograms, with disagreement concerning the number of major vesels and a 70% stenosis occurring approximately 30% of the time) The disagreement in grading regional wall motion abnormalities is even higher. 2 When compared with autopsy measurements of the degree of narrowing, stenotic lesions ranging between 50% and 70% are usually underestimated by angiographers using visual or caliper gradings.3This most likely relates to the observation that the atherosclerotic process tends to be diffuse, and employing the measurement of percent narrowing may not indicate the true severity of the coronary obstruction. 4 The new computer-assisted quantitative techniques using edge detection 5 or videodensitrometric 6 measurements of coronary stenoses with digital subtraction angiography may enhance the accuracy of grading the severity of these lesions. Even if the degree of coronary artery stenoses could be precisely measured by quantitative angiography, the functional or physiologic severity of CAD from a prognostic sense may still not be forthcoming unless coronary reserve capacity can be simultaneously addressed] Investigative efforts are underway to develop techniques for assessing regional myocardial perfusion and coronary flow reserve during angiography using computer-assisted techniques for quantitative myocardial contrast uptake, washout, or both) The functional importance of visualized coronary collaterals must also be taken into account. Although collaterals are demonstrated angiographically, this does not necessarily indicate protection against exercise-induced ischemia, or infarction if the proximal stenosis should become totally occluded. 9 Finally, the extent of myocardium in the risk region distal to a given stenotic vessel cannot easily be ascertained by coronary arteriography alone. Risk areas distal to given locations of coronary stenoses may vary considerably from patient to patient. Some patients with single-vessel disease; particularly involving the proximal portion of the left anterior descending coronary artery, may be at high risk for an adverse outcome, because a large area of the anterior wall and septum is rendered ischemic, particularly at low levels of exercise. Certain patients with multivessel CAD may have an excellent prognosis because of lack of extensive ischemia in the myocardial risk regions of the diseased vessel during stress. This certainly was true for the majority of patients with three-vessel CAD and mild symptoms in the randomized arm of the Coronary Artery Surgery Study (CASS) in which the medically treated group had a surprisingly low 5-year cardiac event rate. 1° In this review, emphasis is placed on the