Role of left ventricular function and Doppler-derived variables in predicting hemodynamic benefits of rate-responsive pacing.

Cardiac hemodynamics were studied in 22 patients (mean age 55 +/- 2 years, range 22 to 73) with rate-responsive pacemakers using the continuous-wave Doppler method to assess ascending aortic blood flow. Compared with constant rate ventricular (VVI) pacing, rate-responsive pacing conferred improvements in exercise capacity (39 +/- 9%, p less than 0.001) and cardiac output (41 +/- 8%, p less than 0.001). Cardiac output increased by 141 +/- 21% over the resting value and 56% of this increase was mediated by the ability of these pacemakers to increase their pacing rate. Doppler-derived peak aortic flow velocity, acceleration and stroke distance were lower during maximal exercise in the rate-responsive mode and there was a trend toward a higher systolic blood pressure response. Neither age nor echocardiographic and Doppler-derived variables (at rest and during peak exercise in the VVI mode) could predict the hemodynamic and functional benefits conferred by rate-responsive pacing during exercise, although left ventricular function had a weak correlation. It was concluded that rate-responsive pacing significantly benefits patients with bradycardia, although the extent of the benefit is not predictable, and that advanced age alone should not be a barrier to the use of a rate-responsive pacemaker.