IMPORTANCE OF HEART-RATE MODULATION ON THE CARDIAC HEMODYNAMICS DURING POSTEXERCISE RECOVERY

The influence of heart rate changes on the recovery of cardiac hemodynamics and lactate clearance after exercise was studied in nine patients with complete atrioventricular (AV) block treated with programmable pacemakers. A preliminary treadmill exercise test in which the pacing rate was externally increased stepwise from 70 to 230 bpm was performed fo determine the maximum exercise duration. Two exercise tests involving an equal amount of exercise load were performed, the pacing rate was either programmed to the basic rate (abrupt decay) or gradually (modulated decay) immediately after exercise termination. Compared with abrupt decay, modulated decay resulted in a higher mean arterial pressure (100 ± 4 mmHg vs 91 ± 5 mmHg, P ± 0.05) and diastolic pressure (76 ± 4 mmHg vs 59 ± 4 mmHg, P < 0.001) immediately on exercise termination. Immediately after exercise and during modulated decay, cardiac output (represented by Doppler derived minute distance] declined gradually and was determined mainly by a higher pacing rate without significant changes in stroke volume. On the other hand, minute distance fell abruptly during abrupt decay (996 ± 107 m at peak exercise and 561 ± 88 m immediately after a rate change at exercise termination, P < 0.01) with a corresponding abrupt increase in systemic vascular resistance. This was later compensated by a gradual increase in stroke volume during the recovery period. The cumulative cardiac output between the two rate changes equalized at the 4th minute of recovery. Abrupt decay was associated with a higher recovery atrial rate (109 ± 5 bpm versus 102 ± 5 bpm at the fifth minute of recovery, P < 0.01) and a higher peak velocity of ascending aortic flow, both suggestive of an enhanced sympathetic level during this mode of recovery. There is a trend toward a higher peak arterial lactate level during abrupt decay, although the overall lactate clearance rates between the two decay modes were similar. Most patients preferred the modulated decay. In conclusion, rate modulation at exercise termination produced more gradual hemodynamic changes compared with abrupt decay. Cardiac hemodynamics was maintained by a compensatory increase in stroke volume and an increase in sympathetic activities after a latent period. Independent of the form of rate modulation, a fixed amount of cardiac output appears necessary to facilitate postexercise recovery after a given workload. Copyright © 1990, Wiley Blackwell. All rights reserved