Residual myocardial ischaemia in first non-Q versus Q wave infarction: maximal exercise testing and ambulatory ST-segment monitoring.

Abstract

In a prospective study of 123 consecutive survivors of a first myocardial infarction (43 non-Q wave, 80 Q wave), we determined the total residual ischaemic burden by use of pre-discharge maximal exercise testing and post-discharge 36 h ambulatory ST-segment monitoring initiated 11 +/- 5 days after the infarction. The prevalence of exercise-induced ischaemic manifestations in the infarct types was similar: chest pain 14% vs 16% and ST-segment depression 54% vs 54%. The ischaemic threshold did not differ either (heart rate at 1 mm of ST-segment depression 120 +/- 27 vs 119 +/- 25 beats.min-1). During early post-discharge daily activities, more patients with non-Q wave infarction demonstrated transient episodes of ST-segment depression: 28% vs 14% (ns). Furthermore, ischaemic episodes were significantly longer (42.5 +/- 50.1 vs 22.0 +/- 20.6 min; P < 0.001), and the ischaemic threshold was significantly lower in non-Q wave infarction (heart rate at onset of ST-segment depression 84 +/- 11 vs 88 +/- 9 beats.min-1; P < 0.05). During 3.5 +/- 0.9 years of follow-up the proportion of patients with > or = 1 ischaemic event (non-fatal reinfarction, angina pectoris, revascularization) was significantly higher in non-Q wave infarction (51%) as compared to Q wave infarction (31%) (P < 0.05). In both infarct types the presence of ST-segment depression on ambulatory recording and exercise testing significantly predicted the development of future angina pectoris, whereas patients at increased risk for subsequent non-fatal reinfarction or cardiac death were not identified.