CHRONOTROPIC INCOMPETENCE IN CHRONIC HEART-FAILURE

Background: The exercise limitation of patients with chronic heart failure may be due in part to an inability to increase heart rate as normal, a limitation sometimes referred to as chronotropic incompetence. This may be due to down regulation of beta receptors. Methods: Fifty-seven patients with chronic heart failure and 14 age-matched controls underwent symptom limited treadmill exercise tests with metabolic gas exchange measurements. Heart rate and blood pressure responses were also recorded. Results: Peak oxygen consumption was reduced in the heart failure patients (19.6 (S.D. +/- 7.6) vs. 35.0 (+/- 9.9); P < 0.001). Heart rate at peak exercise (r = 0.47, P < 0.001), and change in heart rate from rest to peak exercise (r = 0.59; P < 0.001) and rate pressure product at peak exercise (r = 0.56, P < 0.001) all correlated with peak oxygen consumption. The percentage of predicted maximal heart rate at peak exercise correlated poorly with peak oxygen consumption (r = 0.29; P > 0.05). Peak systolic and diastolic blood pressures did not correlate with peak oxygen consumption. Sixteen patients had chronotropic incompetence. There was no significant difference between this group and those without chronotropic incompetence in the intensity of exercise performed, underlying diagnosis, drug therapy or prevalence of atrial fibrillation. There was a trend towards shorter exercise times in the incompetent group (430 (+/- 251) vs. 545 (+/- 216) s; P = 0.08) compared to the other patients. Conclusions: Chronotropic incompetence was seen in <30% of patients with chronic heart failure. However, there are few differences between the group with chronotropic incompetence and the group without. Chronotropic incompetence is thus unlikely to be a major factor limiting exercise capacity in unselected patients with chronic heart failure and is likely to be the major factor limiting exercise in a much smaller proportion of patients.