Continuous ventricular volume assessment for diagnosis and pacemaker control.

Stroke volume measurements made by a catheter-based, right ventricular, intracardiac impedance system at rest and during upright bicycle ergometry were found to compare favorably with measurements made by acetylene rebreathing (r = 0.96, n = 13) and by radionuclide ventriculography (r = 0.96, n = 13) in a 46-year-old male pacemaker-dependent subject. The impedance information was then used to control the ventricular pacing rate during bicycle exercise, utilizing an algorithm that attempts to maintain a constant stroke volume. This resulted in a 23% increase in cardiac output accompanied by a 70% decrease in stroke volume as compared to the values measured during the same exercise at 70 pulses per minute (ppm).