ECHOCARDIOGRAPHIC FLOW FIELD VISUALIZATION DURING MECHANICAL CIRCULATORY SUPPORT IN THE ISOLATED ASSISTED HEART

Intraventricular flow patterns during mechanical circulatory support (MCS) cannot be accessed by clinical imaging; therefore, either computational or in-vitro models are used. However, the complex anatomy of the heart cannot be replicated and simulations inherently rely on assumptions and simplifications. In an isolated porcine heart setup the feasibility of flow measurements by Echocardiographic Particle Image Velocimetry (E-PIV) was evaluated. Similar to cardiac transplantation, porcine hearts (n=8, animal weight: 80-106 kg) were excised and connected to the isolated heart setup. After resuscitation using blood as perfusate, a rotary blood pump was implanted, microbubbles were injected via the left atrium at different support situations and echocardiographic 3-chamber-view B-mode images were recorded with the highest possible frame rate of up to 141 Hz (Philips iE33, X5-1 xMatrix probe). By iterative PIV algorithms using correlation domain averaging and beam sweep correction, flow fields were evaluated for the different hemodynamic situations. All hearts were successfully resuscitated in the isolated heart setup and different hemodynamic situations were adjusted. In the unsupported heart physiologic flow patterns with a large clockwise vortex structure that warrants washout of the whole cardiac chamber were found. With increasing MCS (2200-2700 rpm) the formation of this flow feature is diminished caused by the additional flow sink at the apex. In full support, without aortic valve opening in the left ventricular outflow tract, a stagnant structure was identified, that might be connected to thromboembolic events. For the first time, the contribution of the mitral valve apparatus to blood flow patterns especially in the LVOT, which may be linked to energy loss, thrombus formation and valve deterioration during MCS was investigated under realistic conditions.