[Cardiopulmonary stress: control of the function of frequency variable pacemaker systems]

Based on the linear relationship between cardiac output and oxygen uptake direct breath-to-breath gas exchange measurements during exercise allow accurate determinations of cardiopulmonary function. We used cardiopulmonary exercise testing to assess the physiologic benefit of rate response VVIR pacing in 17 patients with chronotropic incompetence. 13 patients had an activity-rate-response pacemaker, two patients had a temperature-controlled pacemaker and two patients a respiratory-dependent system. Exercise testing was performed with the pacemaker, either programmed to fixed rate VVI or to rate variable VVIR pacing. All patients were exercised on a bicycle using a ramp protocol with 10 to 20 watts/min increments. Maximal oxygen uptake and the anaerobic threshold were determined. Compared with findings in the VVI mode, rate response VVIR pacing increased maximal exercise heart rate from 74 +/- 10 to 118 +/- 21 bpm (p less than 0.001). This increase in heart rate was associated with an increase of maximal oxygen uptake from 14.3 +/- 5 to 18.3 +/- 6 ml/kg per min (p less than 0.04) and a delay of the anaerobic threshold to a higher oxygen consumption of 14.6 +/- 5 vs 10.6 +/- 5 ml/kg per min (p less than 0.04). The individual increase in oxygen uptake was a direct function of the change in exercise heart rate independent of the implanted pacing device. The improved aerobic capacity resulted in a 17% increase in exercise tolerance and a 19% increase of exercise time. Cardiopulmonary exercise testing appears to be a useful noninvasive technique to quantify the cardiopulmonary benefit of rate response pacing.