Restoration of Pulsatile Flow Reduces Sympathetic Nerve Activity Among Individuals With Continuous-Flow Left Ventricular Assist Devices

Abstract

Thirteen patients with implanted Heartmate II CF-LVADs were recruited from the University of Texas Southwestern Medical Center advanced heart failure (HF)/mechanical circulatory support Background-Current-generation left ventricular assist devices provide circulatory support that is minimally or entirely nonpulsatile and are associated with marked increases in muscle sympathetic nerve activity (MSNA), likely through a baroreceptor-mediated pathway. We sought to determine whether the restoration of pulsatile flow through modulations in pump speed would reduce MSNA through the arterial baroreceptor reflex. Methods and Results-Ten men and 3 women (54±14 years) with Heartmate II continuous-flow left ventricular assist devices underwent hemodynamic and sympathetic neural assessment. Beat-to-beat blood pressure, carotid ultrasonography at the level of the arterial baroreceptors, and MSNA via microneurography were continuously recorded to determine steady-state responses to step changes (200-400 revolutions per minute) in continuous-flow left ventricular assist device pump speed from a maximum of 10 480±315 revolutions per minute to a minimum of 8500±380 revolutions per minute. Reductions in pump speed led to increases in pulse pressure (high versus low speed: 17±7 versus 26±12 mm Hg; P<0.01), distension of the carotid artery, and carotid arterial wall tension (P<0.05 for all measures). In addition, MSNA was reduced (high versus low speed: 41±15 versus 33±16 bursts per minute; P<0.01) despite a reduction in mean arterial pressure and was inversely related to pulse pressure (P=0.037). Conclusions-Among subjects with continuous-flow left ventricular assist devices, the restoration of pulsatile flow through modulations in pump speed leads to increased distortion of the arterial baroreceptors with a subsequent decline in MSNA. Additional study is needed to determine whether reduction of MSNA in this setting leads to improved outcomes.

To Pulse or Not to Pulse, Is That the Question?

“…Those living with LVADs constitute a small population but one for whom there has been an enormous investment in resources and personnel to ensure a good and enduring outcome with a high quality of life. The value of MSNA, as revealed by the present literature, [4][5][6] is that it could well be applied in future investigations to define the optimal degree of pulse and diastolic pressure for such individuals. …”

“…4 These investigators focused their attention on the effect of acute alterations in mean and pulse pressures on 1 efferent limb of the arterial baroreceptor reflex arc, postganglionic sympathetic discharge to calf skeletal muscle, which they recorded directly from the fibular nerve. In a previously published experiment by this group, MSNA was recorded under 2 conditions, supine rest and 60° head-up tilt, in 6 patients with implanted left ventricular assist devices (LVADs) providing pulsatile flow and from 11 with nonpulsatile LVADs.…”

“…In those with nonpulsatile compared with pulsatile LVADs, MSNA was 80% higher at rest and 70% higher during tilt, a difference these investigators attributed to diminished arterial mechanoreceptor stretch. 5 Cornwell et al 4 now report the findings of a protocol involving 13 patients with implanted Heartmate II continuous axial-flow devices designed to test the hypothesis that immediate changes in LVAD pump speed would elicit reflex muscle sympathetic firing responses by altering arterial pulse pressure and hence mechanoreceptor input to baroreceptor afferent nerves. 4 With participants supine, MSNA and a photoplethysmographic digital arterial waveform were recorded continuously while the prevailing LVAD pump speed was increased (to unload the left ventricle, reduce aortic valve opening, and diminish pulse pressure) or decreased (to achieve the converse) in 200-to 400-rpm steady-state increments and maintained at each velocity for up to 10 minutes.…”

“…5 Cornwell et al 4 now report the findings of a protocol involving 13 patients with implanted Heartmate II continuous axial-flow devices designed to test the hypothesis that immediate changes in LVAD pump speed would elicit reflex muscle sympathetic firing responses by altering arterial pulse pressure and hence mechanoreceptor input to baroreceptor afferent nerves. 4 With participants supine, MSNA and a photoplethysmographic digital arterial waveform were recorded continuously while the prevailing LVAD pump speed was increased (to unload the left ventricle, reduce aortic valve opening, and diminish pulse pressure) or decreased (to achieve the converse) in 200-to 400-rpm steady-state increments and maintained at each velocity for up to 10 minutes. At each pump speed, the presence of aortic valve opening was determined by echocardiography, and carotid ultrasound was used to quantify the arterial diameter throughout the cardiac cycle for the purpose of estimating, in conjunction with blood pressure, the pulsatile carotid sinus mechanoreceptor distending force achieved.…”

Patient-centered care for left ventricular assist device therapy

“…21 In addition, the long-term effects of non-pulsatile blood flow on end-organ and vascular function are unknown, but may contribute to patient outcomes while on chronic LVAD support. For example, CF LVADs have been found to alter cerebral auto-regulation of blood flow 22 , increase aortic vascular stiffness via alterations in vessel collagen and elastin content 23 , and increase sympathetic nervous system activity 24 . All of these findings in theory could contribute to the pathophysiology of CF LVAD related complications such as gastrointestinal bleeding, hypertension, and stroke.…”