Attenuated Cardiac Sympathetic Responsiveness During Dynamic Exercise in Patients With Heart Failure

Background Cardiac norepinephrine (NE) spillover is increased in patients with chronic heart failure. This elevation is partly due to augmented NE release but also to reduced capacity for cardiac NE removal processes. In patients with mild to moderate heart failure, it is not known whether the described alteration in cardiac sympathetic function also affects cardiac NE spillover during intense sympathetic activation and whether other organs respond in proportion to the heart. Methods and Results Twenty-two patients with heart failure and 15 age-matched healthy subjects were studied. Whole-body and regional (NE) spillovers from the heart and kidneys were assessed at baseline and during supine cycling exercise (10 minutes) with the use of steady-state infusions of tritiated NE (isotope dilution). Cardiac performance was evaluated by means of catheterization of the right side of the heart. Cardiac NE spillover was higher ( P <.05) at baseline in the patient group than in healthy subjects, whereas renal and whole-body NE spillovers were similar between the study groups. During exercise, cardiac NE spillover increased 13-fold ( P <.05) in healthy subjects but only 5-fold ( P <.05) in the cardiac failure group, the latter reaching a lower peak value ( P <.05). In contrast, there was no difference between the study groups in either renal or whole-body NE spillover responsiveness to exercise. Conclusions Patients with mild to moderate heart failure demonstrated a selective attenuation of cardiac sympathetic responsiveness during dynamic exercise. This attenuation may convey reduced inotropic and chronotropic support to the failing heart.