Effect of chronic changes in heart rate on congestive heart failure

Background: Heart rate can affect cardiac function, but the importance of rates lower than 100 paced beats per minute is unknown. We therefore sought to evaluate the impact of different heart rates on ejection fraction, 6-minute walk, and peak oxygen consumption (VO2) in heart failure patients. Methods and Results: We studied 13 pacemaker-dependent New York Heart Association Class III patients with ejection fraction <40%, age 66 +/- 13. Eligible patients included those pacing at least 75% of the time at a lower set rate of 60 ppm. This was a 3-period randomized blinded crossover study. Patients were assigned to pace at 60, 75, or 90 ppm (with rate responsivity to 20 ppm above the lower rate) for 2 months at each setting. At the end of each period, ejection fraction (by nuclear ventriculography) and exercise tolerance (by peak VO2 and 6-minute walk) were assessed. Ejection fraction, peak VO2, and 6-minute walk distance were significantly different among the 3 heart rates. All 3 were depressed at 90 ppm. A heart rate of 90 also led to more clinical deterioration and premature discontinuation from that period. Conclusions: Pacing at a heart rate of 90 led to lower ejection fraction, VO2, 6-minute walk distance and clinical evidence of worsening heart failure as compared with slower heart rates.