Flow through an outlet cannula of a rotary ventricular assist device

Rotary ventricular assist devices (VADs) are primarily used during surgery and short-term postoperative assistance. There are issues involving the use of rotary VADs including the behavior of flow emanating from the assist device which might induce flow irregularities that could potentially lead to stroke or cerebrovascular accident. An in vitro flow visualization study using particle image velocimetry was conducted to evaluate flow fields at the bend of outlet cannulae with angles ranging from 30 degrees to 75 degrees. A multiple disk centrifugal blood pump produced steady, laminar flow fields at the outlet. Flow fields at the bend of each cannula demonstrated the development of a boundary layer along the inner wall and shift of fluid momentum to the outer wall. Stagnant zones along the inner wall were prevalent for each cannula and increased in severity with increasing angle. The outlet flow fields of rotary VADs have the potential to produce thrombus, feasibly leading to thromboembolisms should the bend angle of the outlet cannula be acute enough. Therefore, the placement of the outlet cannula or conduit should be taken into consideration during implantation.