Initial clinical experience with a minute ventilation sensing rate modulated pacemaker: improvements in exercise capacity and symptomatology.

A minute ventilation sensing rate modulated pacemaker was implanted in nine patients with bradycardia. Minute ventilation is sensed in this pacemaker by means of a standard bipolar pacing electrode. Compared with exercise in the constant rate ventricular pacing (VVI) mode at 1 month after pacemaker implantation, rate responsive pacing resulted in an improvement of exercise capacity of 33 +/- 5% (from 437 +/- 42 s in the VVI mode to 593 +/- 57 s in the rate modulated mode, P less than 0.01, Bruce protocol). This improvement was maintained in the seven patients in whom an exercise test was repeated at 3 months after implantation. The pacing rate was significantly correlated with oxygen consumption (r = 0.84 +/- 0.04) and measured minute ventilation (r = 0.76 +/- 0.06). Symptomatology in these patients was assessed by means of self-assessment questionnaires in a double blind, randomized cross-over study in which the pacemaker was alternatively programmed into the VVI and rate modulated modes. Significant improvements in "shortness of breath" and "energy during daily activities" were documented during rate modulated pacing and "palpitations" and "chest pain" were not worsened. Most patients preferred the rate modulated mode during the study. In conclusion, rate modulated pacing by sensing minute ventilation resulted in better exercise capacity and symptomatology. The pacing rate also showed good correlation with the individual's oxygen requirement.