Effect of ventricular function on the exercise hemodynamics of variable rate pacing.

To determine the effect of ventricular function on the exercise hemodynamics of variable rate pacing, 16 selected patients underwent paired, double-blind, randomized exercise tests in single rate demand (VVI) or variable rate (VVIR) pacing modes. Ejection fraction and cardiac index were determined by two-dimensional and Doppler echocardiography at baseline and during peak exercise. Baseline ejection fraction ranged from 14 to 73% and was less than 40% in 6 patients (Group 1) and greater than or equal to 40% in 10 patients (Group 2). Duration of exercise was longer during the VVIR mode (502 s) than during the VVI mode (449 s) (p less than 0.01) and unrelated to baseline ejection fraction. Heart rate during exercise increased 9% in the VVI mode and 35% in the VVIR mode (p less than 0.005). Cardiac index increased 49% in the VVI mode and 83% in the VVIR mode. Analysis of variance for repeated measures showed a significant effect of pacing mode (p less than 0.01) and exercise (p less than 0.001), but not baseline ejection fraction, on cardiac index. Baseline ejection fraction did not correlate with the increase in cardiac index in either pacing mode or with the difference in increase between modes. There was no significant difference between Groups 1 and 2 in exercise duration, peak heart rate-blood pressure (rate-pressure) product, baseline or peak heart rate or baseline or peak cardiac index. Therefore, in selected patients, VVIR pacing during exercise results in an increase in heart rate, duration of exercise and cardiac index that is unrelated to the degree of baseline left ventricular dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)