Computational fluid dynamics analysis of thrombosis potential in left ventricular assist device drainage cannulae

Abstract

Cannulation is necessary when blood is removed from the body, for example in hemodialysis, cardiopulmonary bypass, blood oxygenators, and ventricular assist devices. Artificial blood contacting surfaces are prone to thrombosis, especially in the presence of stagnant or recirculating flow. In this work, computational fluid dynamics was used to investigate the blood flow fields in three clinically available cannulae (Medtronic DLP 12, 16, and 24 F), used as drainage for pediatric circulatory support and to calculate parameters that may be indicative of thrombosis potential. The results show that using the 24 F cannula below flow rates of about 0.75 L/min produces hemodynamic conditions, which may increase the risk of blood clotting within the cannula. No reasons are indicated for not using the 12 or 16 F cannulae with flow rates between 0.25 and 3.0 L/min.

Figure 1

Example of thrombosis inside a 24F Medtronic DLP venous drainage cannula which was used in an animal implant. Similar clots have been found in other cannulae with similar designs.

Figure 2

Schematic diagram of cannulae showing dimensions given in Table 1

Figure 3

Mean percentage errors for the three meshes from the ordered error estimators

Figure 4

Comparison of calculated and experimentally measured pressure drops for the three cannulae

Figure 5

a - Volume with velocity magnitude < 1 mm/s (total LV-cannula volume, excluding outlet length), and b - volume, within just the cannula, with velocity magnitude < 1 mm/s (excluding outlet length). 24 F cannula results are also shown for a non Newtonian blood viscosity model and these results are explained in the Discussion.

Figure 6

Velocity magnitude in 12, 16 and 24 F cannulae with flow rate 0.25 l/min. Only speeds between 0.001 and 0.01 m/s (1 and 10 mm/s) are shown.

Figure 7

a - Volume with shear rate magnitude < 250/s and, b - volume with shear rate magnitude > 2564/s (within cannula, excluding outlet length).

Figure 8

Top: Low shear rate volumes in 12 and 16 F cannulae at 0.25 l/min are similar. Bottom: Decrease in low shear rate volume with increasing flow rate in the 24 F cannula. Shear rates between 0 and 500/s are shown.

Figure 9

Recirculation regions in the tips of the cannulae