Increased cardiac sympathetic nerve activity in heart failure is not due to desensitization of the arterial baroreflex

Abstract

Increased sympathetic drive to the heart worsens prognosis in heart failure, but the level of cardiac sympathetic nerve activity (CSNA) has been assessed only by indirect methods, which do not permit testing of whether its control by arterial baroreceptors is defective. To do this, CSNA was measured directly in 16 female sheep, 8 of which had been ventricularly paced at 200-220 beats/min for 4-6 wk, until their ejection fraction fell to between 35 and 40%. Recording electrodes were surgically implanted in the cardiac sympathetic nerves, and after 3 days' recovery the responses to intravenous phenylephrine and nitroprusside infusions were measured in conscious sheep. Electrophysiological reco..