The effect of heart rate on the working capacity of patients with complete heart block and physiological pacemaker

The effect of heart rate (HR) on maximum working capacity was studied in 18 patients (mean age 55 years) with a physiological pacemaker implanted for chronic complete heart block of different aetiology. Exercise testing was performed by bicycle ergometry in 3 pacing protocols in randomized sequence, and without the patients knowing the preprogrammed pacing mode: 1) VVI pacing at a rate of 30 beats/min--exercise on heart block; 2) VVI pacing at a rate of 70 beats/min; 3) physiological DDD or QT pacing. While patients with heart block had a mean HR of 54 +/- 16 beats/min and working capacity of 81 +/- 31 W, on VVI 70 pacing the values were 73 +/- 9 beats/min (+35%, p < 0.002) and 100 +/- 45 W (+24%, p < 0.008), respectively. Exercise during physiological pacing led to an increase in HR to 140 +/- 15 beats/min (+169%, p < 0.002) and in working capacity to 130 +/- 52 W (+61%, p < 0.002). Thus, the increment in working capacity was 2.5 times higher on physiological than standard ventricular pacing (p < 0.005) if compared with the working capacity of patients with heart block.