SUPERIOR CARDIAC HEMODYNAMICS OF ATRIOVENTRICULAR SYNCHRONY OVER RATE RESPONSIVE PACING AT SUBMAXIMAL EXERCISE - OBSERVATIONS IN ACTIVITY SENSING DDDR PACEMAKERS

The relative hemodynamic profile between dual chamber pacing (DDD) and activity sensing rate responsive pacing (VVIR) was compared in ten patients with dual chamber rate responsive pacemakers (Synergist II). With a double blind, randomized exercise protocol, DDDR pacemakers were programmed into VVI, VVIR, and DDD (AV interval 150 msec) modes and in seven patients the test in the DDD mode was repeated with the AV interval programmed at 75 msec. A treadmill exercise test of 6-minutes duration (2 stages, Stage I at 2 mph, 0% gradient and Stage II at 2 mph, 15% gradient) was performed at each of the programmed settings, with a rest period of 30 minutes in between tests. Cardiac output was assessed using continuous-wave Doppler sampling ascending aortic flow and expressed as a percentage of the value achieved during VVI pacing. During exercise, pacing rate between DDD and VVIR pacing was similar but was higher with DDD at the first minute of recovery (91 +/- 4 vs 81 +/- 3 beats/min, respectively). Cardiac output was significantly higher at rest, during low level exercise, and recovery with DDD pacing compared with VVIR pacing (resting: 21 +/- 14 vs -2 +/- 7%; Stage I: 36 +/- 6 vs 16 +/- 7%; Stage II: 25 +/- 15 vs 10 +/- 8%; recovery: 26 +/- 12 vs 4 +/- 9%; P < 0.05 in all cases). Systolic blood pressure was significantly higher during low level of exercise in the DDD mode. Shortening of the AV interval to 75 msec did not significantly affect cardiac output during exercise, but cardiac output after exercise was reduced (2 +/- 6 vs 23 +/- 6% at an AV interval of 150 msec, P < 0.02). By enhancing the stroke volume, DDD pacing improves cardiac hemodynamics at rest, during low level exercise, and early postexercise recovery.