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

Depressed baroreflex sensitivity (BRS) after acute myocardialinfarction (AMI) is considered an indication of decreased vagaland/or increased sympathetic tone. To determine the effect ofangiotensin converting enzyme inhibitors (ACEI) on BRS afterAMI we studied 27 patients with a first Q wave AMI, no signsof heart failure and no history of arterial hypertension ordiabetes mellitus. An additional group of10 patients with thesame clinical characteristics served as controls. On the 5thday after the onset of AMI, three consecutive boluses of phenylephrinewere given intravenously and baseline BRS was taken as the meanslope of the linear regression lines of RR intervals over systolicblood pressure. QT interval was also measured and correctedaccording to Bazett's formula (QTc). Consequently, a singleoral dose of captopril 50 mg or placebo was given to treatmentor control group patients, respectively; BRS and QTc were reassessedlh later. One hour after captopril administration BRS increasedfrom 5.95±2.80 to 9.14±3.46ms.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±15mmHg (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 observedin any variable compared to baseline. Captopril appears to improveBRS immediately in the early phase of AMI.