DOPPLER-ECHOCARDIOGRAPHIC ASSESSMENT OF THE HEMODYNAMIC BENEFITS OF RATE-ADAPTIVE AV DELAY DURING EXERCISE IN PACED PATIENTS WITH COMPLETE HEART-BLOCK

To determine if rate adaptation of the atrioventricular (AV) delay (i. e., linearly decreasing the AV interval for increasing sinus rate) imp roves exercise left ventricular systolic hemodynamics, we performed pa ired maximal semi-upright bicycle exercise tests (EXTs) on 14 chronotr opically competent patients with dual chamber pacemakers. Nine patient s with complete AV block (CAVB) and total ventricular pacing dependenc e during exercise comprised the experimental group. Pacemakers in thes e patients were programmed randomly to rate adaptive AV delay (AVDR) f or one EXT and fixed AV delay (AVDF) for the other EXT. AVDF was 156 m sec; AVDR decreased linearly from 156-63 msec from rates of 78-142 bea ts/min. The other five patients had intact AV conduction and comprised the control group who were exercised in identical fashion while their pacemakers were inhibited throughout exercise to assure reproducibili ty of hemodynamic measurements between EXTs. Cardiac hemodynamics were calculated using measured Doppler echocardiographic systolic aortic v alve flows recorded suprasternally with an independent 2-MHz Doppler t ransducer during a graded ramp exercise protocol. For analysis, exerci se was divided into four phases to compare Doppler measurements at sub maximal and maximal levels of exercise: rest, early exercise (lst stag e), late exercise (stage preceding peak), and peak. Patients achieved statistically similar heart rates between EXTs at each phase of exerci se. Although at lower levels of exercise cardiac hemodynamics did not differ, experimental patients (with CAVB) showed a statistically signi ficant benefit to cardiac output at peak exercise with heart rates of 129 +/- 13 beats/min (AVDR: 9.4 +/- 2.8 L/min; AVDF: 8.2 +/- 2.6 L/min , P = 0.002), stroke volume (AVDR: 74.1 +/- 25.6 mL; AVDF: 64.3 +/- 24 .4 mL, P = 0.0003), and aortic ejection time (AVDR: 253.3 +/- 35.7 mse c; AVDF: 226.7 +/- 35.0 msec, P = 0.002). Duration of exercise, peak r ate pressure product, peak aortic flow velocities, and acceleration ti mes did not differ. In contrast, control group patients (intact AV con duction throughout exercise) showed no statistical differences between any hemodynamic parameters measured at any phase of exercise from the first to second exercise test. These data demonstrate that systolic c ardiac hemodynamics measured echocardiographically at the high heart r ates achieved with peak exercise are improved with AVDR compared to AV DF in chronotropically competent patients with complete AV block. This is due primarily to improved stroke volume and a longer systolic ejec tion time with AV delay rate adaptation.