Exercise-Induced Increase in Baroreflex Sensitivity Predicts Improved Prognosis After Myocardial Infarction

Abstract

Background— Despite the rational expectation for a survival benefit produced by exercise training among post–myocardial infarction (MI) patients, direct evidence remains elusive. Clinically, changes in autonomic balance toward lower vagal activity have consistently been associated with increased mortality risk; conversely, among both control and post-MI dogs, exercise training improved vagal reflexes and prevented sudden death. Accordingly, we tested the hypothesis that exercise training, if accompanied by a shift toward increased vagal activity of an autonomic marker such as baroreflex sensitivity (BRS), could reduce mortality in post-MI patients. Methods and Results— Ninety-five consecutive male patients surviving a first uncomplicated MI were randomly assigned to a 4-week endurance training period or to no training. Age (51±8 versus 52±8 years), site of MI (anterior 41% versus 43%), left ventricular ejection fraction (52±13 versus 51±14%), and BRS (7.9±5.4 versus 7.9±3.4 ms/mm Hg) did not differ between the two groups. After 4 weeks, BRS improved by 26% ( P =0.04) in trained patients, whereas it did not change in nontrained patients. During a 10-year follow-up, cardiac mortality among the 16 trained patients who had an exercise-induced increase in BRS ≥3 ms/mm Hg (responders) was strikingly lower compared with that of the trained patients without such a BRS increase (nonresponders) and that of the nontrained patients (0 of 16 versus 18 of 79 [23%], P =0.04). Cardiac mortality was also lower among responders irrespective of training (4% versus 24%, P =0.04). Conclusions— Post-MI exercise training can favorably modify long-term survival, provided that it is associated with a clear shift of the autonomic balance toward an increase in vagal activity.