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. 2013 May 16:10:35.
doi: 10.1186/1742-4682-10-35.

Numerical investigation of the effect of cannula placement on thrombosis

ChiWei Ong  1 , Socrates Dokos, BeeTing Chan, Einly Lim, Amr Al Abed, Noor Azuan Bin Abu Osman, Suhaini Kadiman, Nigel H Lovell
Affiliations

Numerical investigation of the effect of cannula placement on thrombosis

ChiWei Ong et al. Theor Biol Med Model. .

Abstract

Despite the rapid advancement of left ventricular assist devices (LVADs), adverse events leading to deaths have been frequently reported in patients implanted with LVADs, including bleeding, infection, thromboembolism, neurological dysfunction and hemolysis. Cannulation forms an important component with regards to thrombus formation in assisted patients by varying the intraventricular flow distribution in the left ventricle (LV). To investigate the correlation between LVAD cannula placement and potential for thrombus formation, detailed analysis of the intraventricular flow field was carried out in the present study using a two way fluid structure interaction (FSI), axisymmetric model of a passive LV incorporating an inflow cannula. Three different cannula placements were simulated, with device insertion near the LV apex, penetrating one-fourth and mid-way into the LV long axis. The risk of thrombus formation is assessed by analyzing the intraventricular vorticity distribution and its associated vortex intensity, amount of stagnation flow in the ventricle as well as the level of wall shear stress. Our results show that the one-fourth placement of the cannula into the LV achieves the best performance in reducing the risk of thrombus formation. Compared to cannula placement near the apex, higher vortex intensity is achieved at the one-fourth placement, thus increasing wash out of platelets at the ventricular wall. One-fourth LV penetration produced negligible stagnation flow region near the apical wall region, helping to reduce platelet deposition on the surface of the cannula and the ventricular wall.

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Figures

Figure 1
Figure 1
Axisymmetric arrangement of cannula, fluid and LV wall domains. The dashed line shows the axis of rotational symmetry and the arrow shows the direction of blood flow across the cavity during the filling phase.
Figure 2
Figure 2
The three different configurations of cannula placement used in the present study. The three different configurations of cannula placement used in simulations. Three different configurations of cannula placement are used in the simulations: (a) near the apex; (b) one fourth of LV and (c) half LV.
Figure 3
Figure 3
Mesh element detail at the interface boundary between the LV wall and blood fluid domains.
Figure 4
Figure 4
Transmitral velocity profile is applied at the inlet.
Figure 5
Figure 5
Instantaneous vorticity scalar fields at different time points (t = 0.42, 0.5 and 0.6 s) showing isolevel contours plot (50 to 300, step = 10, unit = 1/s) for different cannula placements. The vorticity scalar magnitude is shown, with direction perpendicular to the plane of the figures. (a) near the apex, at t = 0.42s; (b) near the apex, at t=0.5s; (c) near the apex, at t=0.6s; (d) one forth LV, at t = 0.42s; (e) one forth LV, at t=0.5s; (f) one forth LV, at t=0.6s; (g) half LV, at t = 0.42s; (h) half LV, at t=0.5s; (i) half LV, at t=0.6s.
Figure 6
Figure 6
Time course of the average vortex intensity in the model under different cannula placements.
Figure 7
Figure 7
Velocity magnitude spatial distribution in the model at t = 0.6 s under different cannula placements.
Figure 8
Figure 8
Time course of total stagnation volume under different cannula placements.
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