The pathophysiologic substrate and the prognostic value of pathologic Q-waves after an acute myocardial infarction are still unclear. To elucidate this problem we stratified 52 postinfarction patients into those with Q-infarctions (n = 23) and those with non-Q-infarctions (n = 29). The localization and the extent of reversible and irreversible perfusion defects were assessed using dipyridamole-thallium-201 tomography (SPECT); in addition, coronary morphology, left ventricular wall motion, and prognosis were followed for 1 year. The Q-wave group showed a total defect size of 44.0 +/- 15.3% and a reversible defect size of 13.9 +/- 10% of the left ventricular myocardium. This was not significantly different from the non-Q-wave group, with a mean total defect of 35.2 +/- 20.7% and a mean reversible defect of 16.6 +/- 12.9%. However, the size of the irreversible defects in Q-wave infarctions was larger than in non-Q-wave infarctions (30.6 +/- 18.2% vs 18.6 +/- 17.5%; p less than 0.02). In addition, the relative portion of the reversible defect was larger in non-Q-infarctions than in Q-infarctions (55.9 +/- 25.7% vs 35.7 +/- 21.3%; p less than 0.01). Q-wave infarctions had a significantly lower LVEF of 55.7 +/- 15.4%, as compared to non-Q-infarctions (66.2 +/- 11.9%) (p less than 0.02). The extent of disease, as measured by coronary score and regional wall motion, was similar, but non-Q-wave infarctions were associated with a higher reinfarction rate (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)