The axial continuous-flow blood pump: Bench evaluation of changes in flow associated with changes of inflow cannula angle

Abstract

Changes in the geometry of the HeartMate II (HMII) inflow cannula have been implicated in device thrombosis post-implant. The purpose of this in vitro study was to evaluate what effects changing the angle of the cannula in relation to the pump may have on pump flow and arterial pressure, under simulated inflow conditions. The HMII with an inflow cannula was mounted on a mock loop consisting of a pulsatile pneumatic ventricle to simulate the native ventricle. The angles of the HMII in relation to the inflow cannula were adjusted by separate fixed gooseneck holders. A custom-made miniature steerable camera was introduced into a flexible portion of the HMII inflow cannula. Endoscopic views of various types of inflow cannula constriction (bending, squeezing, stretching and twisting) were recorded, and pump flow and systemic arterial pressure (AoP) were assessed during each simulation. Baseline mean pump flow (3.5 liters/min) and mean AoP (91.5 mm Hg) were unchanged by bending maximally in 2 different directions, twisting up to 30°, stretching (compression or extension), or occluding the inflow graft <90%. However, mean pump flow and mean AoP decreased substantially when the inflow graft became occluded by ≥90% by sliding or squeezing. "Less-than-critical" obstruction (what we define here as <90%) of the HMII inflow cannula did not reveal substantial changes in pump flow or AoP. Data suggest that a major alteration to inflow cannula geometry is required to achieve clinically relevant hemodynamic changes. These data confirm that minor changes in angulation of the inflow cannula have no impact on flow through the device.