Clinical characteristics of unstable angina before acute myocardial infarction

Four hundred and seventy-six patients with acute myocardial infarction (AMI) were interviewed to evaluate the clinical features of angina before AMI. Two hundred and sixty-six of the 476 patients had angina before AMI, of which 137 had new onset of angina within 2 months before AMI, and 129 had chronic angina of more than 2 months before AMI. Forty of the 129 chronic angina patients noted worsening of symptoms within 2 months before AMI. Of the 177 patients with new onset angina or worsening angina such as unstable angina, the incidence of new onset angina was higher than that of worsening angina. Twenty-eight (70%) of the 40 patients with worsening of symptoms had started with effort angina, 16 of whom turned to resting angina from effort angina at the onset of unstable angina in spite of the fact that 12 had worsening of effort angina. Of the 137 patients with new onset angina, 65 (40%) started with resting angina and 72 (53%) with exertional angina. In the former group, 43 (66%) developed AMI within 1 week after the onset of angina, which was greater than 19 (26%) in the latter group. These results may suggest that the appearance of the resting angina would herald AMI in both groups of unstable angina. The onset of resting angina in the group of new onset angina could be the warning of AMI development within a shorter interval than those of exertional angina.