Good exercise capacity at hospital discharge predicts recovery of baroreflex sensitivity after myocardial infarction

Myocardial infarction results in depressed baroreflex sensitivity, which has been shown to be associated with increased risk of ventricular arrhythmias and sudden death. We measured baroreflex sensitivity in 37 patients with acute myocardial infarction before hospital discharge and 3 months after the infarction to find out whether the baroreflex sensitivity recovers hiring that period. In addition, baroreflex sensitivity was assessed in 15 healthy controls. Baroreflex sensitivity was assessed from the regression line relating the change in R-R interval to the change in systolic blood pressure following, an intravenous bolus injection of phenylephrine. There was a wide inter-individual variation in the change of baroreflex sensitivity (Delta baroreflex sensitivity) in infarction patients, but the average baroreflex sensitivity showed no significant change during the 3-month follow-up (10.2 + 5.6 to 11.8 +/- 7.5 ms. mmHg(-1), ns) and remained lower than the baroreflex sensitivity of the controls (16.4 +/- 9.7 ms. mmHg(-1), P<0.05). Delta Baroreflex sensitivity correlated significantly with exercise capacity measured before hospital discharge. When the patients were divided into tertiles according to the Delta baroreflex sensitivity (-3.3 +/- 1.5 ms. mmHg(-1) in the lowest tertile, 1.0 +/- 1.0 ms. mmHg(-1) in the middle tertile and 7.5 +/- 4.0 ms. mmHg(-1) in the highest tertile the exercise capacity was found to increase from the lowest to the highest tertile (exercise time 357 +/- 115 s, 418 +/- 126 s and 461 +/- 141 s, respectively, P<0.05 lowest vs highest tertile). Patients with a low exercise tolerance (exercise time <360 s) showed a significantly smaller Delta Baroreflex sensitivity than patients with a good exercise tolerance (exercise time greater than or equal to 480 s) (-0.5 +/- 4.4 vs 5.3 +/- 5.4 ms. mmHg(-1), P<0.05), respectively. Delta Baroreflex sensitivity was not related to the location or type of infarction, thrombolytic therapy, presence of angina pectoris or left ventricular function at the time of discharge. In conclusion, exercise capacity assessed before hospital discharge seems to be a predictor of baroreflex sensitivity recovery in patients with a recent myocardial infarction.