Complex stenosis morphology frequently occurs in patients with unstable angina pectoris. However, its relation to transient myocardial ischemia and hospital outcome has not been ascertained. To address this issue, 88 patients with significant (greater than or equal to 50%) coronary artery disease presenting with angina--new onset (n = 38), worsening (n = 20) or at rest (n = 30)-were studied. Patients with left main artery disease, normal coronary arteries or occlusion of the ischemia-related arteries were not included in the study. Continuous electrocardiographic recordings were obtained during the first 24 hours. Angiography was performed within 1 week from admission. Complex morphology was defined as any stenosis with irregular borders, overhanging edges or intracoronary thrombus. Only data referring to the in-hospital outcome were considered in this study. Adverse end points were sudden death, myocardial infarction and emergency revascularization. Analysis of the angiograms revealed a complex morphology in 58 patients (group 1). The remaining 30 patients served as control subjects (group 2). Thirty-two of the 58 group 1 patients had an unfavorable clinical outcome (positive predictive value, 55%). A similar outcome occurred in only 2 of the 30 group 2 patients (negative predictive value, 93%). Of the 32 group 1 patients who had an unfavorable clinical outcome, 29 had a cumulative duration of transient myocardial ischemia of greater than or equal to 60 minutes per 24 hours. A similar duration of ischemia, however, was observed in another 6 group 1 and in 8 group 2 patients.(ABSTRACT TRUNCATED AT 250 WORDS)