56 The Influence of Chronotropic Incompetence on Exercise Capacity in Chronic Heart Failure

Introduction Increased cardiac output during exercise is the result of greater stroke volume and an increase in heart rate. It is therefore assumed that a limitation to heart rate rise (HRR) in response to activity, chronotropic incompetence (CI), could contribute to the exercise intolerance that is characteristic of chronic heart failure (CHF). However, HRR is closely related to workload and subjects with impaired exercise capacity have a lower peak heart rate (PHR) and a lower HRR. Hence, whether a limited increase in heart rate (HR) during exercise in patients with CHF is aetiological in their exercise limitation or merely a bystander remains unproven. The aim of this study was to examine the effects of correcting CI in patients with CHF on peak and submaximal exercise capacity. Methods We enrolled 50 subjects with CHF due to left ventricular systolic dysfunction (LVSD), (left ventricular ejection fraction Results Rate-adaptive pacing led to higher mean (SE) peak HR (128 (21) vs 107 (28) bpm; p Conclusions Exercise intolerance due to breathlessness and fatigue is a cardinal feature of CHF and remains a problem for many patients despite optimal medical and device therapy. Agents that lower HR and induce CI are proven to improve outcomes for patients with CHF due to LVSD yet traditional models of heart failure suggest that a lower cardiac output, potentially the consequence of CI, reduces blood supply to exercising muscles thereby limiting work. By demonstrating that higher HR throughout exercise is not associated with greater exercise capacity in CHF patients, we propose that CI does not play a major role in exercise intolerance in CHF.