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 130 bpm was performed to 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 less than 0.05) and diastolic pressure (76 +/- 4 mmHg vs 59 +/- 4 mmHg, P less than 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 less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)