Acute effect of captopril administration on baroreflex sensitivity in patients with acute myocardial infarction.

Depressed baroreflex sensitivity (BRS) after acute myocardial infarction (AMI) is considered an indication of decreased vagal and/or increased sympathetic tone. To determine the effect of angiotensin converting enzyme inhibitors (ACEI) on BRS after AMI we studied 27 patients with a first Q wave AMI, no signs of heart failure and no history of arterial hypertension or diabetes mellitus. An additional group of 10 patients with the same clinical characteristics served as controls. On the 5th day after the onset of AMI, three consecutive boluses of phenylephrine were given intravenously and baseline BRS was taken as the mean slope of the linear regression lines of RR intervals over systolic blood pressure. QT interval was also measured and corrected according to Bazett's formula (QTc). Consequently, a single oral dose of captopril 50 mg or placebo was given to treatment or control group patients, respectively; BRS and QTc were reassessed 1 h later. One hour after captopril administration BRS increased from 5.95 +/- 2.80 to 9.14 +/- 3.46 ms.mmHg-1 (P < 0.0001); QTc increased from 414 +/- 46 to 425 +/- 46 ms (P < 0.0001), systolic blood pressure decreased from 125 +/- 19 to 115 +/- 15 mmHg (P = 0.0002), while heart rate did not change significantly. Baseline BRS was correlated only with age (r = -0.74, P < 0.0001). In the control group, 1 h after placebo, no difference was observed in any variable compared to baseline. Captopril appears to improve BRS immediately in the early phase of AMI.