CHRONIC RATE-ADAPTIVE PACING IN PATIENTS WITH HEART-FAILURE

Twenty patients (complete AV block n = 13, sick sinus syndrome n = 4 ( replacement of a VVI system), bradyarrhythmia n = 3) with rate-adaptiv e pacemakers (respiration volume guided n = 10, QT-driven n = 1, dual sensor (QT/activity) system n = 9) were randomly assessed by ergospiro metry after 4 weeks of VVI- (70 bpm), VVIR(1)-(70-110 bpm, low upper r ate) and VVIR(2)-pacing (70-130 bpm, high upper rate). Oxygen uptake ( VO2), work load (W), and heart rate were determined at peak exercise ( max) and at the anaerobic threshold (AT). In the whole population, rat e adaptation led to a significantly higher VO2-max than VVI-pacing for both VVIR(1)-(15.5 +/- 5.1/12.6 +/- 4.1 mg/kg/min, 28 +/- 37%, p < 0. 01) and VVIR(2)-pacing (14.8 +/- 4.4/12.6 +/- 4.1 ml/kg/min, 20 +/- 23 %, p < 0.01). At the AT, however, VO2 was significantly improved only by the VVIR(1) mode (low upper rate, 9.8 +/- 2.5/8.0 +/- 2.1 ml/kg/min , 28 +/- 36%, p < 0.01). Regarding only patients with moderately limit ed exercise capacities (Weber class C, n = 11), rate adaptive VVIR(1) and VVIR(2) pacing could not produce a significant increase of VO2-max and VO2-AT. In contrast, patients with severely reduced exercise capa cities (Weber class D, n = 9) significantly profited from the rate ada ptation, but only in the VVIR(1), mode (VO2-max 48 +/- 45%, VO2-AT 51 +/- 38%, p < 0.01), Thus, in the whole population an increase of oxyge n uptake and of exercise workload at the anaerobic threshold could onl y be achieved by pacing with the low upper rate of 110 bpm. By this, p articularly patients with heart failure and a severely limited exercis e tolerance (Weber D) had a significant benefit. Therefore, the upper rate should be programmed in a lower range in patients with heart fail ure, at least for rate-adaptive ventricular pacemaker systems.