Relation between ischemia time, infarct size, and left ventricular function in humans

Experimental studies indicate that duration of ischemia is a major determinant of myocardial infarct size, but only limited information is available about the relation between ischemia time and infarct size in individual patients. This prospective study sought to document the role of ischemia time as a determinant of infarct size in humans. We studied 61 patients (50 men, 11 women) 57 +/- 11 years old admitted with a first infarct (31 anterior, 30 inferior) who underwent continuous 12-lead ECG monitoring to document ischemia time. Infarct size (32-point QRS score on day 7) and changes in regional myocardial wall motion (echocardiography) during the following month were related to ischemia time. Among patients with < 3 hours of ischemia (n = 16), mean infarct size on day 7 was 21 +/- 13% of potential infarct size; in patients with 3 to 6 hours of ischemia (n = 23), infarct size was 38 +/- 18% of potential (P < .05 versus 0 to 3 hours of ischemia); and in patients with 6 to 9 hours of ischemia (n = 10), infarct size was 66 +/- 14% of potential (P < .05 versus 3 to 6 hours). In contrast, the 12 patients with an ischemia time > 9 hours had a final infarct size of 77 +/- 10% of potential (P < .01 versus 3 to 6 hours). Multivariate regression identified size of risk region, duration of ischemia, and degree of initial ST-segment elevation as independent predictors of infarct size, of which the most important variable was ischemia time. The regression models accurately predicted both individual absolute infarct size (R2 = .83) and individual infarct/risk ratio (R2 = .74). Patients with < 6 hours of ischemia exhibited significant recovery of myocardial wall motion by day 7 (wall motion score, 2.1 +/- 1.4 versus 5.7 +/- 3.2 on day 1, P < .01). Patients with 6 to 9 hours of ischemia had some recovery by 1 month (score, 6.3 +/- 4.4 versus 10.9 +/- 3.8 on day 1, P < .01), but patients with > 9 hours of ischemia had little recovery of wall motion by 1 month (score, 10.3 +/- 4.5 versus 12.8 +/- 3.1 on day 1, P < .05). Measurement of ischemia time allows improved prediction of infarct size in humans. Significant myocardial salvage and functional recovery may be achieved by reperfusion up to 9 hours after coronary occlusion. Continuous ST-segment monitoring should be used to measure ischemia time and guide interventions to reperfuse the infarct artery.