Impaired Heart Rate Responses and Exercise Capacity in Heart Failure Patients With Paced Baseline Rhythms

Background: Conduction system disease and beta-blocker therapy are both common among heart failure (HF) patients and contribute to increasing reliance on paced rhythms. We hypothesized that many HF patients dependent on pacing have suboptimal heart rate responses and associated limitations in exercise capacity. Methods and Results: We studied 122 HF patients (left ventricular ejection fractions <= 40%) referred for cardiopulmonary exercise testing, comparing those with pacing at baseline with those with native rhythms. The paced group (PG) had lower resting (71 +/- 9 vs 75 +/- 15 beats/min; P = .048) and peak heart rates (103 +/- 22 vs 127 +/- 27 beats/min; P < .0001). Although beta-blockers were prescribed with similar frequency in both groups (90% vs 85%), average dose was higher in the PG. Inotropic reserve (oxygen pulse) was similar in both groups (11.1 +/- 3.3 vs 11.1 +/- 3.4 mL/beat; P = .94), consistent with equivalent stroke volumes, but chronotropic incompetence was higher (95% vs 71%, P = .001) and peak VO2 was lower (12.2 +/- 3.4 vs 14.2 +/- 4.1 mL/kg/min; P = .004) in the PG. Conclusions: Chronotropic incompetence and exercise capacity are worse in HF patients depending on paced heart rate responses. This has implications for quality of life as well as advanced therapy choices based on exercise capacity. Reevaluating beta-blocker dosing and optimizing pacemaker programming may therefore benefit the growing population of HF patients with device-dependent rhythms. (J Cardiac Fail 2011:17:188-195)