Increase in cardiac output with rate-responsive pacemaker.

Patients with myocardial insufficiency or patients during high cardiac work loads increase cardiac output (CO) only through an increase in heart rate (HR), which is not possible with a VVI pacemaker. This clinical study tests the hypothesis that the respiratory-dependent pacemaker (RDP) is able to increase CO by an increase in HR. A multiprogrammable RDP (BIOrate RDP 2, Alpha, Köln, West Germany) was implanted in 21 patients (16 men and 5 women) for ventricular pacing. The mean age of the patients was 68.1 +/- 9.5 years (+/- standard deviation). Since the RDP can be programmed either in the RDP or VVI mode, all patients served as their own control. During follow-up examinations 4 to 6 weeks after implantation, an exercise ECG and a determination of CO during rest and exercise using equilibrium-radionuclide ventriculography were performed. One pacemaker has had to be explanted because of "end of life." No other RDP is malfunctioning. There was a significant increase in HR in all patients during exercise with the RDP versus the VVI mode (105.5 +/- 5.9 versus 84.5 +/- 7.0 bpm; p less than 0.05). CO increased during exercise to 10.6 +/- 0.8 L/min (VVI mode) and 12.7 +/- 1.5 L/min (RDP mode) (p = not significant). RDPs are reliable systems for patients in whom dual-chambered pacemakers are contraindicated (e.g., patients with bradyarrhythmias). The RDPs are able to increase CO by 26 to 35% compared with the VVI mode because of an increase in HR.