Novel ventricular apical cannula: in vitro evaluation using transparent, compliant ventricular casts

The geometric configuration of the cannula connection to the left ventricular (LV) apex was studied with respect to several characteristics defining functionality and compatibility. The authors had previously determined, through in vivo studies in sheep, that the design of the cannula used with a dynamic blood pump for LV circulatory support can significantly affect the hemodynamics by improving both the bypass flow rate and the fluid dynamics within the ventricle. The tip of the cannula can aid in preventing wall to wall ventricular collapse, as well as septal shift, due to reduced LV pressure. Proper surgical placement of the cannula with respect to the endocardial surface of the LV can also be simplified by the tip geometry. To investigate the anatomic interaction and fluid dynamics of apical cannulation, transparent compliant casts of bovine LVs were fabricated for in vitro flow visualization. Two different heart geometries were cast, end systolic and end diastolic. The latter was fitted with a pericardial mitral valve and pressurized in a pulsatile fashion to simulate the wall movement of a beating heart. The internal flow and anatomy were visualized with fluorescent particle tracking velocimetry. These studies were performed with conventional cannula tips, as well as a novel, trumpet mouth cannula. The visualization clearly shows the dramatic differences in flow between the geometries tested, and strongly advocates a trumpet mouth design. This novel tip demonstrated excellent placement, beneficial stenting, and improved blood flow by reducing apical stasis and recirculation. Ongoing evaluation of these and future geometries include the application of in vitro endoscopy, quantitative velocimetry, and extension to dilated human ventricles.