Pathogenesis and natural course of unstable angina--a prospective and retrospective study.

Abstract

In order to evaluate the natural history of unstable angina and to clarify the relationship between unstable angina and myocardial infarction, we studied the natural course of 128 patients with unstable angina prospectively and analyzed the characteristics of preinfarctional angina in 250 patients with acute myocardial infarction in a retrospective study. Prospective Study : During a 3-month follow-up period, 23 of 128 patients (18.0%) developed myocardial infarction, 40 (31.3%) remained with angina pectoris and 65 (50.8%) became free from anginal attacks. No significant difference was found in the occurrence rate of myocardial infarction between the patients without a history of myocardial infarction (Group I) and those with a history (Group II). The persistence rate of angina pectoris was higher in patients with a history of angina pectoris than in those without a history. Newly developed effort angina (EA) remained or developed into myocardial infarction more frequently than newly developed, rest angina (RA) (p < 0.05). Disappearance rate of angina in RA of the crescendo type was higher than EA of the crescendo type. Similarly, new RA disappeared more frequently than new EA. In Group I no significant differences in the occurrence rate of myocardial infarction and in the persistence and the disappearance rate of angina pectoris were observed between the prolonged type and the frequent type of angina. In Group II, however, the occurrence rate of myocardial infarction in the prolonged type of angina was higher than in the frequent type, but the disappearance rate of angina in the former type was significantly higher than that in the latter type (p < 0.05). The coronary artery lesion was more severe in Group II than in Group I. Patients with persisting angina pectoris complicated more commonly with severe coronary artery lesion than those with disappearing angina pectoris. Retrospective Study : One hundred and thirty-nine out of 250 patients (55.6%) with acute myocardial infarction had a history of angina pectoris before the onset of infarct. Sixty patients (24.0%) had unstable angina (new onset 13.6% ; crescendo type 10.4%), 28 (11.2%) stable EA, 21 (8.4%) RA and 30 (12.0%) a prodrome. The incidence of preinfarctional angina in patients with previous myocardial infarction was 70.5% and this value was higher than that in those without previous myocardial infarction (48.8%). At the end of the follow-up period (mean : 7 months), 126 out of 186 patients (67.7%) had no postmyocardial infarctional angina, 43 (23.1%) had EA, 12 (6.4%) had RA and 5 (2.7%) developed myocardial infarction. While the new onset type of preinfarctional unstable angina disappeared in 70.4% after the onset of infarction, the disappearance rate of the crescendo type was only 30.0% (p < 0.05). The coronary artery lesion in patients with crescendo angina was more severe than that in those with new onset angina.