Baroreflex sensitivity, clinical correlates, and cardiovascular mortality among patients with a first myocardial infarction: A prospective study

Abstract

Experimental studies have shown that among dogs with a healed myocardial infarction, depressed baroreflex sensitivity (BRS) identifies a subgroup at higher risk for sudden death. We have examined the relation among BRS, several clinical cardiovascular variables, and subsequent mortality in 78 patients below the age of 65 years who have had a first myocardial infarction. BRS was assessed by calculating the regression line relating phenylephrine-induced increases in systolic blood pressure to the attendant changes in the RR interval. A reduced BRS primarily reflects an impairment in the vagal efferent component of the baroreceptor reflexes. The BRS of the entire population was 7.8 ± 4.9 msec/mm Hg. BRS was lower among patients with an inferior myocardial infarction (6.1 ± 3.3 vs. 8.9 ± 5.8 msec/mm Hg, p = 0.03), with a three- versus a one-vessel disease (4.8 ± 2.7 vs. 7.1 ± 3.1 msec/mm Hg, p = 0.04), and with episodes of ventricular tachycardia (5.1 ± 3.0 vs. 8.3 ± 5.1, p = 0.03). There was no correlation between BRS and left ventricular ejection fraction or with mean pulmonary capillary wedge pressure at peak exercise, but a correlation (r = 0.35, p < 0.001) was present with exercise tolerance. During the 24 months mean follow-up period, there were six cardiovascular deaths (7.6%), and four were sudden. The BRS of the decreased patients were strikingly lower than those of the survivors (2.4 ± 1.7 vs. 8.2 ± 4.8 msec/mm Hg, p = 0.004), and mortality dramatically increased from 2.9% (two of 68) to 40% (four of 10) (p < 0.001) in the presence of a markedly depressed BRS (<3.0 msec/mm Hg). Even among patients with depressed left ventricular function, mortality was associated with reduced BRS. This clinical prospective study suggests that analysis of baroreflex sensitivity in patients after myocardial infarction provides novel information on cardiovascular pathophysiology and may contribute to more accurate identification of individuals at high risk for subsequent mortality.