The effect of rate-adaptive pacing on exercise capacity, plasma lactate and catecholamines in pacemaker patients

In order to evaluate the behaviour of metabolic variables of pacemaker patients under exercise conditions, we examined - in addition to the common exercise-related parameters, heart rate and work load, central venous blood temperature, plasma lactate, plasma adrenaline and noradrenaline of patients with temperature controlled rate adaptive pacemakers (Intermedics Nova MR(TM)). All patients underwent two bicycle exercise tests, one in the VVI 70 mode, one in the VVIR mode. The sequence of the tests was randomised. We found a 16% improvement of maximum work load in the temperature controlled mode compared with the VVI mode; the calculation of total energy consumption showed a 33% improvement with VVIR pacing. During exercise, the patients showed a slight increase in intrinsic heart rate which, however, was significantly (20%) less than the increase in stimulation rate with rate adaptive pacing. The improvement of maximum exercise capacity is probably related to an elevated aerobic energy production, which is reflected by a reduction in plasma lactate with rate adaptation. At the same work load of 50 W, the plasma lactate concentration with VVIR pacing was 23% lower than with VVI pacing; at maximum work load, in the VVIR mode we found the plasma lactate concentration to be 7% higher than in the VVI mode (despite a 33% higher total energy consumption). The catecholamine levels at rest were elevated compared with the age related normal values reflecting pre-existing impaired cardiac function. On exercise, the catecholamine concentrations correlated with work load. The detection of plasma lactate may represent a beneficial new approach towards acute evaluation of the effects of pacemaker therapy for the patient even at submaximal work loads. Further investigations are necessary to determine the suitability of this method for routine purposes.