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[A study on the clinical significance of myocardial ischemic attack and its causative mechanism in angina pectoris. An assessment using Holter's electrocardiogram].

The purpose of this study is to clarify the causative mechanism as well as the clinical significance of myocardial ischemic attacks in patients suffering from angina pectoris. The subjects were 127 patients upon whom 24-hour Holter electrocardiographic monitoring was performed. The patients were classified into the four types of angina pectoris: exertional angina (56 cases, EA), exertional and rest angina (28 cases, ERA), and rest angina (4 cases, RA), all of which show ST-segment depression during ischemic attacks; and variant angina (39 cases, VA) which shows ST-segment elevation. The Holter electrocardiographic findings were classified into the four above-mentioned types and were analyzed. The frequency of symptomatic ischemic attacks in descending order was EA, ERA, RA and VA, while the frequency of asymptomatic ischemic attacks was in the reverse order. EA was significantly higher than the other three types of angina. In the daytime, however, the frequency of ischemic attacks in descending order was EA, ERA, RA and symptomatic and asymptomatic ischemic attacks was in the same order. The peak occurrence of hourly ischemic attacks was at 10:00 am and 1:00 pm in the case of EA, 7:00 am in the case of ERA, 2:00 am in the case of RA and 5:00 am in the case of VA. The magnitude and duration of ischemic attacks and maximal heart rates during attacks were greater in symptomatic ischemic attacks than in asymptomatic ischemic attacks in each type of angina pectoris. The maximal heart rates during symptomatic ischemic attacks were in descending order, EA, ERA, RA and VA. On the other hand, the maximal heart rates during attacks recorded on a Holter electrocardiograph were lower than those during induced attacks on treadmill exercise testing, and the difference in rates was significant in both EA and VA. In patients with angina pectoris showing ST-segment depression during attacks, no relation was observed between the magnitude and duration of ST-segment depression and the severity of coronary artery lesions. In conclusion, it may be stated that the situation and the mechanism of the occurrence of the myocardial ischemic attacks varied based on the types of angina pectoris. Moreover, it was clarified that the mechanism of ischemic attacks was different between spontaneous and exercise induced attacks as the threshold of the occurrence of the former group was lower than that of the latter group. Therefore, it was concluded that the circadian alternation of the increased coronary vascular tonus is one of main causes of the spontaneous ischemic attacks.