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 ofventricular arrhythmias and sudden death. We measured baroreflexsensitivity in 37 patients with acute myocardial infarctionbefore hospital discharge and 3 months after the infarctionto find out whether the baroreflex sensitivity recovers duringthat period. In addition, baroreflex sensitivity was assessedin 15 healthy controls. Baroreflex sensitivity was assessedfrom the regression line relating the change in R-R intervalto the change in systolic blood pressure following an intravenousbolus injection of phenylephrine. There was a wide inter-individualvariation in the change of baroreflex sensitivity (Abaroreflexsensitivity) in infarction patients, but the average baroreflexsensitivity showed no significant change during the 3-monthfollow-up (10.2 +5.6 to 11.8 ± 7.5 ms. mmHg ^–1,ns) and remained lower than the baroreflex sensitivity of thecontrols (16.4 ± 9.7 ms. mmHg^–1, P<0.05). Baroreflexsensitivity correlated significantly with exercise capacitymeasured before hospital discharge. When the patients were dividedinto tertiles according to the 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± 40 ms. mmHg^–1 in the highest tertile) the exercisecapacity was found to increase from the lowest to the highesttertile (exercise time 357 ± 115 s, 418 ± 126s and 461 ± 141 s, respectively; P<0.05 lowest vshighest tertile). Patients with a low exercise tolerance (exercisetime <360 s) showed a significantly smaller Abaroreflex sensitivitythan patients with a good exercise tolerance (exercise time480s) ( – 0.5±4.4 vs 5.3 ± 5.4ms. mmHg^–1,P<0.05), respectively. Baroreflex sensitivity was not relatedto the location or type of infarction, thrombolytic therapy,presence of angina pectoris or left ventricular function atthe time of discharge. In conclusion, exercise capacity assessedbefore hospital discharge seems to be a predictor of baroreflexsensitivity recovery in patients with a recent myocardial infarction.