Improved left ventricular unloading and circulatory support with synchronized pulsatile left ventricular assistance compared with continuous-flow left ventricular assistance in an acute porcine left ventricular failure model

Abstract

Objective: Controversy exists regarding the optimal pumping method for left ventricular assist devices. The purpose of this investigation was to test the hypothesis that pulsatile left ventricular assist synchronized to the cardiac cycle provides superior left ventricular unloading and circulatory support compared with continuous-flow left ventricular assist devices at the same level of ventricular assist device flow. Methods: Seven male pigs were used to evaluate left ventricular assist device function using the TORVAD synchronized pulsatile-flow pump (Windmill Cardiovascular Systems, Inc, Austin, Tex) compared with the Bio-Medicus BPX-80 continuous-flow centrifugal pump (Medtronic, Inc, Minneapolis, Minn). Experiments were carried out under general anesthesia, and animals were instrumented via a median sternotomy. Hemodynamic measurements were obtained in the control state and with left ventricular assistance using the TORVAD and BPX-80 individually. Left ventricular failure was induced with suture ligation of the mid-left anterior descending coronary artery, and hemodynamic measurements were repeated. Results: During left ventricular assist device support, mean aortic pressure and total cardiac output were higher and left atrial pressure was lower with pulsatile compared with continuous flow at the same ventricular assist device flow rate. During ischemic left ventricular failure, pulsatile left ventricular support resulted in higher total cardiac output (5.58 AE 1.58 vs 5.12 AE 1.19, P < .05), higher mean aortic pressure (67.8 AE 14 vs 60.2 AE 10, P < .05), and lower left atrial pressure (11.5 AE 3.5 vs 13.9 AE 6.0, P < .05) compared with continuous flow at the same left ventricular assist device flow rate. Conclusion: Synchronized, pulsatile left ventricular assistance produces superior left ventricular unloading and circulatory support compared with continuous-flow left ventricular assist at the same flow rates.

Flow Modulation Algorithms for Continuous Flow Left Ventricular Assist Devices to Increase Vascular Pulsatility: A Computer Simulation Study

“…Modulation of blood pump motor speeds/flow has been suggested as a potential mechanism to artificially increase vascular pulsatility in both ventricular assist devices 2,5,19,24,26,33,34 and total artificial heart. 10,16,17,27 Flow modulation of ventricular assist devices are affected by the timing of flow modulation to the native myocardial contraction.…”

“…Early VAD modulation strategies focused on asynchronous modulation of LVAD flow as it was simpler to implement. 2, 24 Cox et al, 5 Letsou et al, 19 and Shi et al 26 simulated sinusoidal synchronous LVAD flow modulation but did not vary the timing of LVAD flow modulation. Vandenberghe et al varied the timing of synchronous support but did not vary the LVAD flow modulation amplitude or pulse width.…”

Hemodynamic effects of various support modes of continuous flow LVADs on the cardiovascular system: A numerical study

“…in which SHE represents the extra energy required for generation of pulsatile flow (PF) in terms of energy (not pressure) units and is thus a physiologically relevant measure of pulsatility because the generation of PF in the body is dependent on an energy gradient rather than a pressure gradient [23]. …”

Creating adequate pulsatility with a continuous flow left ventricular assist device

“…It has been postulated that within clinical operating ranges, pulsatile flow pumps provide more flow, and this may account for the differences in unloading. This issue was addressed by Letsou et al [36], who compared hemodynamics in seven male pigs supported with pulsatile flow or continuous flow LVADS and found that at the same flow rate, pulsatile flow LVADs demonstrated a higher mean aortic pressure and total cardiac output, while the left atrial pressure was lower. The effects of decreased ventricular unloading were nicely illustrated by the Columbia group, which found lower levels of serum brain natriuretic peptide and extracellular matrix biomarkers in 31 pulsatile flow as compared with 30 continuous flow LVAD patients [37].…”