Heart rate response to graded exercise correlates with aerobic and ventilatory capacity in patients with heart failure

Background : Autonomic dysfunction and reduced exercise tolerance are typical features of patients with congestive heart failure (CHF). Baro‐chemoreflex balance and organ response may have a common role in conditioning exercise tolerance, ventilation, and chronotropic competence in patients with CHF. Hypothesis : We tested the hypothesis that there is a relationship between functional capacity and chronotropic competence to exercise in CHF. Methods : In all, 48 stable outpatients with CHF (age 65 ± 10 years, 41 men, NYHA class 2.1 ± 0, ejection fraction 31 ± 7%, peak VO 2 16 ± 4 ml/kg/min) performed cardiopulmonary exercise testing (CPX). Heart rate (HR) response to exercise was assessed by the chronotropic index (CRI). The CRI was calculated by the following formula: CRI = peak HR ‐ rest HR/220 ‐ age ‐ rest HR × 100 (normal value > 80%). The relationship of CRI to peak oxygen consumption (VO 2 ) and ventilation/carbon dioxide production (VE/VCO 2 ) ratio was examined. A group of 33 healthy controls underwent CPX as well. Results : The CRI correlated directly with peak VO 2 (r = 0.638, p<0.001) and inversely with VE/VCO 2 (r = −0.492, p < 0.001) in patients with CHF. A CRI< 78% identified patients with CHF and a peak VO 2 < 20 ml/kg/min, area under the receiver operating curve (AUROC): 0.76,95% confidence interval (CI) 0.60–0.92. A CRI< 74% predicted exercise hyperventilation in CHF (AUROC: 0.71 for VE/VCO 2 >30, 95% CI 0.53–0.88). The CRI was not significantly related either to peak VO 2 or to VE/VCO 2 in the control group. Conclusions : In patients with mild to moderate CHF, CRI correlates with functional capacity. This relationship adds new data on pathophysiologic grounds and supports the routine incorporation of CRI into CPX interpretation.