PHYSICAL WORK CAPACITY WITH RATE-RESPONSIVE VENTRICULAR PACING (VVIR)VERSUS DUAL-CHAMBER PACING (DDD) IN PATIENTS WITH NORMAL AND DIMINISHED LEFT-VENTRICULAR FUNCTION

To determine the benefit of atrial contribution on work capacity in re lation to left ventricular ejection fraction, we studied 17 patients ( 68 +/- 13 years) with dual chamber pacemakers (DDD) implanted for high degree atrioventricular (AV) block. In random order they were assigne d to fate responsive ventricular (VVIR) and to atrial triggered ventri cular (VDD) stimulation. Maximum oxygen uptake (max VO2), that correla tes best with work capacity, was measured by spiroergometry at a respi ratory quotient of 1.1 during treadmill exercise test. Left ventricula r ejection fraction at rest was determined by radionuclide ventriculog raphy during VDD-stimulation and an AV delay of 150 ms. There were no differences between these two pacing modes relating heart rate, blood pressure, minute ventilation, exercise duration and maximal work load. In eight patients with an ejection fraction > 50% (60 +/- 10%), but n ot in nine patients with an ejection fraction < 50% (41 +/- 10%), maxi mum oxygen uptake was significantly higher (P < 0.01) during atrial tr iggered ventricular pacing (1440 +/- 533 ml/min) compared with rate re sponsive ventricular pacing(1328 +/- 536 ml/min). Thus, rate responsiv e single chamber pacemakers largely enable the same work capacity as d ual chamber pacemakers in patients with high degree AV block. Patients with normal left ventricular function may profit most from preserved AV synchrony as shown by the higher maximum oxygen uptake on exercise.