The Fluid Mechanics of Transcatheter Heart Valve Leaflet Thrombosis in the Neo-Sinus
Background—Transcatheter heart valve (THV) thrombosis has been increasingly reported. In these studies, thrombus quantification has been based on 2D assessment of a 3D phenomenon.
Methods—Post-procedural four-dimensional, volume-rendered CT (4DCT) data of CoreValve, Evolut R, and SAPIEN 3 transcatheter aortic valve replacement (TAVR) patients enrolled in the RESOLVE trial were included in this analysis. Patients on anticoagulation were excluded. SAPIEN 3 and CoreValve/Evolut R patients with and without hypo-attenuated leaflet thickening (HALT) were included in order to study differences between groups. Patients were classified as having THV thrombosis if there was any evidence of HALT. Anatomical and THV deployment geometries were analyzed, and thrombus volumes were computed through manual 3D reconstruction. We aimed to identify and evaluate risk factors that contribute to THV thrombosis through the combination of retrospective clinical data analysis and in vitro imaging in the space between the native and THV leaflets (neo-sinus).
Results—SAPIEN 3 valves with leaflet thrombosis were on average 10% further expanded (by diameter) than those without (95.5 ± 5.2% vs. 85.4 ± 3.9%; p<0.001). However, this relationship was not evident with the CoreValve/Evolut R. In CoreValve/Evolut Rs with thrombosis, the thrombus volume increased linearly with implant depth (R2 = 0.7; p < 0.001). This was not seen in the SAPIEN 3. The in vitro analysis showed that a supra-annular THV deployment resulted in a nearly 7-fold decrease in stagnation zone size (velocities less than 0.1 m/s) when compared to an intra-annular deployment. In addition, the in vitro model indicated that the size of the stagnation zone increased as cardiac output decreased.
Conclusions—While TAVR thrombosis is a multi-factorial process involving foreign materials, patient-specific blood chemistry and complex flow patterns, our study indicates that deployed THV geometry may have implications on the occurrence of thrombosis. In addition, a supra-annular neo-sinus may reduce thrombosis risk due to reduced flow stasis. While additional prospective studies are needed to further develop strategies for minimizing thrombus burden, these results may help identify patients at higher thrombosis risk and aid in the development of next generation devices with reduced thrombosis risk.
- Received May 17, 2017.
- Revision received July 1, 2017.
- Accepted July 11, 2017.