Quantitative Assessment of Inflow Malposition in Two Continuous-Flow Left Ventricular Assist Devices

We previously investigated preoperative variables associated with qualitative inflow cannula malposition in the HeartMate II (Thoratec-Abbott, Abbott Park, IL) continuous-flow left ventricular assist device. In this report, we assess inflow cannula malposition quantitatively in recipients of both the HeartMate II and the HeartWare (Medtronic-HeartWare, Minneapolis, MN) and examine its association with device thrombosis.

Malposition was quantified based on angular deviation from a hypothetic ideal inflow cannula position in two orthogonal computed tomography imaging planes. Ideal position lies on a line from the apex to the center of the mitral valve. Positive anterior plane angulation indicates deviation toward the superior free wall; negative, toward the inferior wall. Positive lateral plane angulation indicates deviation toward the septum; negative, toward the lateral wall. Device thrombosis was assessed based on clinical criteria.

Fifty-four HeartMate II patients and 68 HeartWare patients were analyzed. Inflow cannula deviation was significantly higher for HeartMate II than for HeartWare (anterior plane angle 36.7 ± 16.8 versus -18.7 ± 11.6 degrees, p < 0.001; lateral plane angle 23.7 ± 20.1 versus 0.2 ± 15.0 degrees, p < 0.001. Pump thrombosis occurred in 31% of HeartMate II patients and 2.9% of HeartWare patients (p < 0.001). In a multivariate model, HeartMate II and increasing inflow cannula deviation toward the septum were associated with higher thrombosis risk (odds ratio 1.35 per 10-degree increase).

We found distinct device-dependent differences in inflow cannula positioning and thrombosis, with HeartWare showing both less malposition and less thrombosis. Malposition toward the ventricular septum may contribute to pump thrombosis through a vicious cycle of suction events, low flow, and speed reduction.