COMPARISON OF VENTRICULAR-FUNCTION IN ATRIAL RATE-ADAPTIVE VERSUS DUAL-CHAMBER RATE-ADAPTIVE PACING DURING EXERCISE

The hemodynamic effects of two different pacing modes-rate adaptive at rial (AAIR) versus dual chamber (DDDR) pacing-were assessed in 12 pati ents with DDDR pacemakers during upright bicycle exercise first-pass r adionuclide angiography using a multiwire gamma camera with tantalum-1 78 as a tracer. All patients had sinus node disease with intact AV con duction. Patients exercised to the same heart rate in random order in these two different pacing modes, AAIR and DDDR with AV delay (of too msec) selected to maintain 100% ventricular capture. Cardiac output in creased significantly above baseline values during exercise in both pa cing modes: 154 +/- 41 % (mean +/- SEM, P = 0.002) with AAIR, versus 9 5 +/- 24% (P = 0.004) with DDDR (P = NS between the two modes). The pe ak filling rate, likewise, increased in both pacing modes (2.3 +/- 0.2 1 end-diastolic volumes/sec to 3.8 +/- 0.32 end-diastolic volumes/sec in AAIR [P = 0.0004] and 2.2 +/- 0.18 end-diastolic volumes/sec to 3.4 +/- 0.27 end-diastolic volumes/sec in DDDR [P = 0.0008]). LV ejection fraction was normal at rest (60 +/- 4%, SEM) and did not significantl y change with submaximal exercise in either pacing mode (both 56%, P = NS). No significant changes in end-diastolic volume or stroke volume indexes occurred with exercise in either pacing mode. Our study demons trates that in patients with normal resting LV function, AAIR and DDDR pacing are equally effective in attaining appropriate increases in ca rdiac output and LV filling during exercise.