Heart rate variability and physical performance changes induced by biventricular pacing in congestive heart failure

Abstract

Cardiac resynchronization therapy (CRT) is a well-accepted therapy in patients with advanced, congestive heart failure (HF). In these patients, changes of mean heart rate (HR), heart rate variability (HRV) and physical performance after starting CRT have not been fully investigated. In this study we rewieved data stored on a CRT-D (Contak-Renewal II, Guidant, USA) implanted in 28 pts (mean age 60.6±3.8 years, QRS duration 149.6 ±6.8 msec, LVEF 19±0.9%) with symptomatic CHF (functional NYHA class >II) despite optimal pharmacological treatment. Sexteen pts have had ischemic dilated cardiomyopathy. Over a period of 16 weeks, weekly changes of minimum HR and mean HR, standard deviation of mean R-R intervals (SDANN) and degree of physical activity done by each patient, measured by Activity Log Index (AL) of the device, were analysed. Moreover, a cardiopulmonary exercise testing was performed before and 4 months after implantation. Results after 16 weeks, CRT-D determined a significant decrease of minimum and mean HR (67.6 ±14 vs 57.4±2.6, and 79.4±15.2 vs 72.7±2.9 bpm, respectively, p<0.04) and a marked increase of SDANN (64.6±28.7 vs 89.7±16 msec, p<0.004). Moreover, after 4 months of continuous pacing, a significant increase of functional capacity of pts, measured by AL (from 4.6±1.5 to 12.2±2.9 %units, (p<0.001) and by VO2 max (from 12.8±1.3 to 17.7±1.4 mlkgmin, p<0.002) was observed. Conclusions in pts with advanced CHF, CRT provides a marked reduction of sympathetic delivery with a gradual increase of parasympathetic activity; these autonomic tone changes are linked to a marked increase of physical performance of CHF pts. Favourable changes of HRV behavior and of functional capacity may suggest a better mid-term prognosis in CHF pts.