Effects of propranolol on recovery of heart rate variability following acute myocardial infarction and relation to outcome in the Beta-Blocker Heart Attack Trial

This study evaluated the effects of propranolol on recovery of heart rate variability (HRV) after acute myocardial infarction and its relation to outcome in the Beta-blocker Heart Attack Trial (BHAT). Beta blockers improve mortality after acute myocardial infarction, but through an unknown mechanism. Depressed HRV, a measure of autonomic tone, predicts mortality after acute myocardial infarction. Whether β blockers influence recovery of HRV after acute myocardial infarction, and thereby improve outcome, is unknown. We compared 24-hour HRV parameters at 1 week after acute myocardial infarction and after 6 weeks of treatment with propanolol (n = 88) or placebo (n = 96). The relation between 25-month outcome (death/acute myocardial infarction/congestive heart failure), propranolol treatment, and HRV was further analyzed. After 6 weeks, high-frequency (HF) power (log-normalized), an index of vagal tone, increased more in propranolol-treated patients (4.28 ± 0.1 to 5.17 ± 0.09 ms2) than in placebo-treated patients (4.26 ± 0.09 to 4.77 ± 0.1 ms2, p