Relationship between impaired chronotropic response cardiac output during exercise, and exercise tolerance in patients with chronic heart failure

Abstract

The present study was undertaken to investigate the relationship between the extent of impaired chronotropic response and cardiac output during exercise, and exercise tolerance in patients with chronic heart failure. The subjects consisted of 24 patients (mean 60.1 ± 14.0 years) who had mild chronotropic incompetence. Cardiopulmonary exercise testing was performed in all patients, and heart rate (HR), anaerobic threshold (AT), maximum oxygen uptake (peak V̇O2), slope of the regression line relating the ventilatory equivalent to carbon dioxide output (V̇E/V̇CO2 slope), and exercise time were measured. Cardiac output (CO) was measured by a thoracic bioimpedance method and cardiac index (CI) was calculated. Plasma norepinephrine (NE) was measured at rest and immediately after the exercise test. The changes in HR, NE, and CI from the resting state to immediately after exercise were calculated as ΔHR, ΔNE, and ΔCI, respectively. The ΔNE was converted to a logarithmic scale and ΔHR/logΔNE was used as a parameter of HR response to sympathetic nerve stimulation. The results were as follows: HR and NE in the resting state had no correlation with AT and with peak V̇O2. ΔHR/logΔNE correlated positively with both AT and peak V̇O2, and negatively with the V̇E/V̇CO2 slope. ΔHR/logΔNE correlated positively with peak CI, %ΔCI, and ΔCI/exercise time. The data suggest that one of the mechanisms of low exercise tolerance in chronic heart failure patients was due to an inadequate increase in CO response against exercise caused by an impaired HR response to increased NE. Copyright © 2003 by the Japanese Heart Journal.