GOOD EXERCISE CAPACITY AT HOSPITAL DISCHARGE PREDICTS RECOVERY OF BAROREFLEX SENSITIVITY AFTER MYOCARDIAL-INFARCTION

Myocardial infarction results in depressed baroreflex sensitivity, whi ch 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 a nd 3 months after the infarction to find out whether the baroreflex se nsitivity recovers hiring that period. In addition, baroreflex sensiti vity was assessed in 15 healthy controls. Baroreflex sensitivity was a ssessed from the regression line relating the change in R-R interval t o the change in systolic blood pressure following, an intravenous bolu s injection of phenylephrine. There was a wide inter-individual variat ion in the change of baroreflex sensitivity (Delta baroreflex sensitiv ity) in infarction patients, but the average baroreflex sensitivity sh owed 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). Delt a Baroreflex sensitivity correlated significantly with exercise capaci ty 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 th e middle tertile and 7.5 +/- 4.0 ms. mmHg(-1) in the highest tertile t he exercise capacity was found to increase from the lowest to the high est tertile (exercise time 357 +/- 115 s, 418 +/- 126 s and 461 +/- 14 1 s, respectively, P<0.05 lowest vs highest tertile). Patients with a low exercise tolerance (exercise time <360 s) showed a significantly s maller 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, th rombolytic therapy, presence of angina pectoris or left ventricular fu nction at the time of discharge. In conclusion, exercise capacity asse ssed before hospital discharge seems to be a predictor of baroreflex s ensitivity recovery in patients with a recent myocardial infarction.