The influence of infarct site on rate of recovery of baroreflex sensitivity after acute myocardial infarction

Abstract

Depression of baroreflex sensitivity (BRS) after myocardial infarction (MI) is a well known phenomenon. However, the mechanism involved is complex and unclear. There has been contradicting data on the magnitude of depression of BRS in anterior vs inferior MI. Little is known about the effects of infarct site on the improvement of BRS after MI although it has been shown to improve as early as 3 weeks and become near normal values at about 6 months after MI. We have studied the influence of infarct site on the early improvement of BRS after MI. Forty one first MI patients (average age 64±20 years, 29 male and 15 anterior) we recruited in the study. Infarct site was determined using standard electrocardiographic criteria and BRS was measured using phenylephrine test at pre-discharge (average day 7 post MI) and repeated at follow-up (average day 42 post MI). Average BRS in the whole study population was 6.7 ± 1.0 (S.E.M.) ms/mmHg predischarge had significantly improved to 8.3 ± 1.2 ms/mmHg at follow-up (p<0.05, paired t-test). However, when infarct site was taken into account, we found a significant improvement of BRS only in the anterior group (from 6.6 ± 2.3 to 9.0 ± 2.8 ms/mmHg, p<0.05, paired t-test). There was negligible improvement in the inferior MI group (from 6.7±1.3 to 7.9±1.4 ms/mmHg, p = n.s.) The results of our study suggest that BRS depression after MI could possibly be caused by a different mechanisms in inferior MI when compared with anterior MI. Direct damage to cardiac nerve endings may be the predominant pathophysiology in inferior MI causing a delay in recovering whereas in anterior. MI, BRS depression is mainly due to mechanical effects of 'pump failure' which recovers early with reperfusion.