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 VO2 16 +/- 4 ml/kg/min) performed cardiopulmonary exercise testing (CPX). Heart rate (HR) response to exercise was assessed by the chronotropic index (CRT). The CRT was calculated by the following formula: CRT = peak HR - rest HR/220 - age - rest HR X 100 (normal value > 80%). The relationship of CRT to peak oxygen consumption (VO2) and ventilation/carbon dioxide production (VE/VCO2) ratio was examined. A group of 33 healthy controls underwent CPX as well. Results: The CRI correlated directly with peak VO2 (r = 0.638, p < 0.001) and inversely with VE/VCO2 (r = -0.492, p < 0.001) in patients with CHF. A CRI < 78% identified patients with CHF and a peak VO2 < 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/VCO2 > 30, 95% CI 0.53-0.88). The CRI was not significantly related either to peak VO2 or to VE/VCO2 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.