Impact of 6 months of therapy with carvedilol on muscle sympathetic nerve activity in heart failure patients.

BACKGROUND The long-term effects of carvedilol on muscle sympathetic nerve activity (MSNA) and muscle blood flow at rest and exercise in patients with chronic heart failure (CHF) remain unknown. METHODS AND RESULTS Twenty-six patients (New York Heart Association class II-III) were randomized to carvedilol or placebo. Blood pressure, heart rate, MSNA, and forearm vascular resistance (FVR) at rest and during isometric forearm exercise (10% and 30% maximal voluntary contraction) were assessed before and after 6 months. Seven patients did not complete the study. Paired data were obtained in 19 (carvedilol 12, placebo 7). Carvedilol significantly decreased MSNA levels and heart rate at rest (-13 +/- 2 versus 3 +/- 8 bursts/min, P = .0001 and -16 +/- 3 vs -4 +/- 6 bpm, P = .05, respectively) and peak exercise (30% = -20 +/- 5 versus -3 +/- 7 bursts/min, P = 0.05 and -19 +/- 4 versus -4 +/- 6 bpm, P = 0.03, respectively) when compared with placebo. Carvedilol did not change a magnitude of response of MSNA and heart rate during exercise (-10 +/- 3 versus -7 +/- 2 bursts/min, P = 0.7 and 11 +/- 3 versus 6 +/- 1, P = .6, respectively). FVR was unchanged by carvedilol. When MSNA was quantified by burst incidence, the strength of reduction in MSNA was attenuated but still greater than placebo. CONCLUSIONS Carvedilol reduces MSNA in patients with CHF. Carvedilol does not reduce FVR at rest or during isometric exercise.