Ventricular Flow Field Visualization During Mechanical Circulatory Support in the Assisted Isolated Beating Heart

P Aigner,K Fraser,H Schima,Y Choi,M Schweiger,U Kertzscher,N Cesarovic,M Hübler,F Lemme,M Granegger

doi:10.1007/s10439-019-02406-x

Abstract

Investigations of ventricular flow patterns during mechanical circulatory support are limited to in vitro flow models or in silico simulations, which cannot fully replicate the complex anatomy and contraction of the heart. Therefore, the feasibility of using echocardiographic particle image velocimetry (Echo-PIV) was evaluated in an isolated working heart setup. Porcine hearts were connected to an isolated, working heart setup and a left ventricular assist device (LVAD) was implanted. During different levels of LVAD support (unsupported, partial support, full support), microbubbles were injected and echocardiographic images were acquired. Iterative PIV algorithms were applied to calculate flow fields. The isolated heart setup allowed different hemodynamic situations. In the unsupported heart, diastolic intra-ventricular blood flow was redirected at the heart’s apex towards the left ventricular outflow tract (LVOT). With increasing pump speed, large vortex formation was suppressed, and blood flow from the mitral valve directly entered the pump cannula. The maximum velocities in the LVOT were significantly reduced with increasing support. For the first time, cardiac blood flow patterns during LVAD support were visualized and quantified in an ex vivo model using Echo-PIV. The results reveal potential regions of stagnation in the LVOT and, in future the methods might be also used in clinical routine to evaluate intraventricular flow fields during LVAD support.

Highlights

Over the past years mechanical circulatory support (MCS) therapy has progressively improved
Once blood enters the ventricular cavity, it traverses in a large clockwise vortex from the cardiac base to the apex, which is directed towards the left ventricular outflow tract (LVOT).[51]
Velocities in the LVOT were reduced with increasing left ventricular assist devices (LVAD) support and a flow channel guiding blood from the mitral valve directly towards the LVAD inflow cannula was created

Summary

Introduction

Over the past years mechanical circulatory support (MCS) therapy has progressively improved. Two-year survival rates of patients with rotary blood pumps (RBP) used as left ventricular assist devices (LVAD) have increased to almost 80%.28. Adverse events such as thromboembolism and major bleeding complications hinder the further success of the therapy.[28]. These adverse events have been attributed to the altered and non-physiologic blood flow patterns within the pump and/or the altered flow field within the assisted ventricle.[3,4,36,45,46]. Energy dissipation is reduced by this vortical flow pattern by avoiding rapid accelerations and gradients; improving contractile efficiency.[1,2,10,42] Since alterations in these vortical flow patterns are associated with different pathological states, they may be even used as a predictor for impending cardiovascular diseases.[19,22,23,39]

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Conclusion