The influence of heart rate on the maximal work capacity was investigated in 18 patients (mean age 55 years) with a physiological pacemaker implanted on account of chronic complete atrioventricular block of different aetiology. Twelve patients with a dominating atrial sinus activity had a dual chamber DDD pacemaker and six patients with dominating atrial fibrillation or flutter had a single chamber QTVVIR pacemaker. The exercise test was made on a bicycle ergometer using three stimulation regimes in randomized order and without the patient's knowledge of the programmed mode of pacing: 1. VVI pacing with frequency of 30/min exercise on AV block, 2. VVI pacing with a frequency of 70/min, 3. Uhysiological DDD or QT pacing. Patients with atrioventricular block attained an average heart rate of 54 + 9/min and a work capacity of 81 + 31 W. During VVI pacing a mean frequency of 73 +/- 9/min was achieved (+35%, P less than 0.002) and a work capacity of 100 +/- 45 W (+24%, P less than 0.008). The load during physiological stimulation led to an increased heart rate, i.e. to 140 +/- 15/min (+169%, P less than 0.002) and work capacity to 130 +/- 52 W (+61%, P less than 0.002). The increment of work capacity was thus 2.5 times greater during physiological than during standard ventricular pacing (P less than 0.005), when compared with the work capacity of patients during AV block. A more extensive investigation is needed to identify patients who will benefit maximally from physiological pacing.

Keywords: Cardiac Pacing, Artificial; Exercise Test /methods/; Female; Heart Block /diagnosis/; Heart Rate; Humans; Male; Middle Aged