Patients With Continuous-Flow Left Ventricular Assist Devices Provide Insight in Human Baroreflex Physiology

Abstract

The superior clinical outcome of new continuous-flow left ventricular assist devices (LVADs) challenges the physiological dogma that cardiovascular autonomic homeostasis requires pulsatile blood flow and pressure. We tested the hypothesis that continuous-flow LVADs impair baroreflex control of sympathetic nerve traffic, thus further exacerbating sympathetic excitation. We included 9 male heart failure patients (26-61 years; 18.9-28.3 kg/m(2)) implanted with a continuous-flow LVAD. We recorded ECG, respiration, finger blood pressure, brachial blood pressure, and muscle sympathetic nerve activity. After baseline measurements had been taken, patients underwent autonomic function testing including deep breathing, a Valsalva maneuver, and 15° head-up tilt. Finally, we increased the LVAD speed in 7 patients. Spontaneous sympathetic baroreflex sensitivity was analyzed. Brachial blood pressure was 99±4 mm Hg with 14±2 mm Hg finger pulse pressure. Muscle sympathetic nerve activity bursts showed a normal morphology, were linked to the cardiac cycle, and were suppressed during blood pressure increases. Mean burst frequency was lower compared with age- and body mass index-matched controls in 2 patients, slightly increased in 4 patients, and increased in 2 patients (P=0.11). Muscle sympathetic nerve activity burst latency and the median values of the burst amplitude distribution were similar between groups. Muscle sympathetic nerve activity increased 4±1 bursts per minute with head-up tilt (P<0.0003) and decreased 3±4 bursts per minute (P<0.031) when LVAD speed was raised. The mean sympathetic baroreflex slope was -3.75±0.79%/mm Hg in patients and -3.80±0.55%/mm Hg in controls. We conclude that low pulse pressure levels are sufficient to restrain sympathetic nervous system activity through baroreflex mechanisms.