SEATTLE — A heart rate of 90 beats per minute was detrimental in a study of pacemaker-dependent patients with heart failure, Krishnamurti Rao reported at the annual meeting of the Heart Failure Society of America.
Thirteen patients in a crossover study spent 2 months with the heart rate set at 60, 75, or 90 beats per minute (bpm), then were randomized to 2 months at one of the other settings, and then 2 months at the third of the three settings. At 90 bpm, patients had significantly lower ejection fractions and reduced exercise tolerance as measured by maximal oxygen consumption (peak VO2) and walked significantly shorter distances on 6-minute walk tests, compared with the periods when heart rates were set to 75 or 60 bpm.
“These findings suggest that a mild tachycardia of even 90 [bpm], when chronic, can lead to left ventricular dysfunction,” said Mr. Rao, who conducted the study with associates on the faculty of the University of Maryland, Baltimore, and currently is a student at Boston University. He has no affiliation with the companies that make pacemakers or heart medications.
Patients also fared worse clinically at a setting of 90 bpm, compared with the other two settings. Clinical deterioration caused four patients in the 90-bpm period and one patient in the 60-bpm period to discontinue that setting before the end of the 2 months. Symptoms worsened in some patients immediately upon starting the 90-bpm rate and in others several weeks after changing rates, he noted. Two patients had their rates turned down to 85 or 80 bpm 3–4 weeks into the 90-bpm period.
The study could not determine the optimal heart rate. Based on the data available, the investigators suggest that pacemaker rates should not be set at more than 75 bpm.
Mean peak VO2 at 60 bpm was 11 mL/kg per minute, at 75 bpm was 11.3 mL/kg per minute, and at 90 bpm was 9.5 mL/kg per minute. The exercise tolerance findings may even underestimate the negative effect of the 90 bpm, because one patient who deteriorated clinically was unable to exercise, he said.
Mean ejection fractions at 60 bpm were 33%, at 75 bpm were 30%, and at 90 bpm were 25%. On the 6-minute walk test, the mean distance was 938 feet at 60 bpm, 996 feet at 75 bpm, and 888 feet at 90 bpm.
Chronic use of β-blockers is known to improve cardiac function, though it has not been clear whether the benefits derive from their effects on heart rate or from other actions, he said.