Chronic heart failure, chronotropic incompetence, and the effects of β blockade

Objective: To establish the prevalence of chronotropic incompetence in a cohort of patients with chronic heart failure (CHF) taking modern medications for heart failure, and whether this affected exercise capacity and predicted prognosis. Methods: Heart rate response to exercise was examined in 237 patients with CHF in sinus rhythm, who were compared with 118 control volunteers. The percentage of maximum age predicted peak heart rate (%Max-PPHR) and percentage heart rate reserve (%HRR) were calculated, with a cut off of, 80% as the definition of chronotropic incompetence for both. Patients were followed up for an average (SD) of 2.8 (9) years. Mortality was related to peak oxygen consumption (pVO(2)), and the presence or absence of chronotropic incompetence. Results: %Max-PPHR, 80% identified 103 (43%) and %HRR, 80% identified 170 patients (72%) as having chronotropic incompetence. Chronotropic incompetence was more common in patients taking beta blockers than in those not taking b blockers as assessed by both methods (80 (49%) v 23 (32%) by %Max-PPHR and 123 (75%) v 47 (64%) by %HRR, respectively). Patients with chronotropic incompetence by either method had a lower pVO(2) than those without. These differences remained significant for both patients taking and not taking a b blocker. %HRR, Max-PPHR%, and HRR were related to New York Heart Association class and correlated with pVO(2). There was no difference in the slopes relating heart rate to pVO(2) between patients with and those without chronotropic incompetence (6.1 (1.7) v 5.1 (1.8), p = 0.34). During an average 2.8 year follow up 40 patients (17%) died. In Cox proportional hazard models, pVO(2) was the most powerful predictor of survival and neither measure of chronotropic incompetence independently predicted outcome. Conclusions: pVO(2) is a powerful marker of prognosis for patients with CHF whether they are taking b blockers or not. A low heart rate response to exercise in patients with CHF correlates with worse exercise tolerance but is unlikely to contribute to exercise impairment.