The Fluid Mechanics of Transcatheter Heart Valve Leaflet Thrombosis in the Neosinus.

BACKGROUND: Transcatheter heart valve (THV) thrombosis has been increasingly reported. In these studies, thrombus quantification has been based on a 2-dimensional assessment of a 3-dimensional phenomenon. METHODS: Postprocedural, 4-dimensional, volume-rendered CT data of patients with CoreValve, Evolut R, and SAPIEN 3 transcatheter aortic valve replacement enrolled in the RESOLVE study (Assessment of Transcatheter and Surgical Aortic Bioprosthetic Valve Dysfunction With Multimodality Imaging and Its Treatment with Anticoagulation) were included in this analysis. Patients on anticoagulation were excluded. SAPIEN 3 and CoreValve/Evolut R patients with and without hypoattenuated leaflet thickening were included to study differences between groups. Patients were classified as having THV thrombosis if there was any evidence of hypoattenuated leaflet thickening. Anatomic and THV deployment geometries were analyzed, and thrombus volumes were computed through manual 3-dimensional 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 (neosinus). RESULTS: SAPIEN 3 valves with leaflet thrombosis were on average 10% further expanded (by diameter) than those without (95.5±5.2% versus 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 finding was not seen in the SAPIEN 3. The in vitro analysis showed that a supraannular THV deployment resulted in a nearly 7-fold decrease in stagnation zone size (velocities <0.1 m/s) when compared with an intraannular deployment. In addition, the in vitro model indicated that the size of the stagnation zone increased as cardiac output decreased. CONCLUSIONS: Although transcatheter aortic valve replacement thrombosis is a multifactorial 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 supraannular neosinus may reduce thrombosis risk because of reduced flow stasis. Although 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.

Valve Type, Size, and Deployment Location Affect Hemodynamics in an In Vitro Valve-in-Valve Model.

OBJECTIVES: The purpose of this study was to optimize hemodynamic performance of valve-in-valve (VIV) according to transcatheter heart valve (THV) type (balloon vs. self-expandable), size, and deployment positions in an in vitro model. BACKGROUND: VIV transcatheter aortic valve replacement is increasingly used for the treatment of patients with a failing surgical bioprosthesis. However, there is a paucity in understanding the THV hemodynamic performance in this setting. METHODS: VIV transcatheter aortic valve replacement was simulated in a physiologic left heart simulator by deploying a 23-mm SAPIEN, 23-mm CoreValve, and 26-mm CoreValve within a 23-mm Edwards PERIMOUNT surgical bioprosthesis. Each THV was deployed into 5 different positions: normal (inflow of THV was juxtaposed with inflow of surgical bioprosthesis), -3 and -6 mm subannular, and +3 and +6 mm supra-annular. At a heart rate of 70 bpm and cardiac output of 5.0 l/min, mean transvalvular pressure gradients (TVPG), regurgitant fraction (RF), effective orifice area, pinwheeling index, and pullout forces were evaluated and compared between THVs. RESULTS: Although all THV deployments resulted in hemodynamics that would have been consistent with Valve Academic Research Consortium-2 procedure success, we found significant differences between THV type, size, and deployment position. For a SAPIEN valve, hemodynamic performance improved with a supra-annular deployment, with the best performance observed at +6 mm. Compared with a normal position, +6 mm resulted in lower TVPG (9.31 ± 0.22 mm Hg vs. 11.66 ± 0.22 mm Hg; p < 0.01), RF (0.95 ± 0.60% vs. 1.27 ± 0.66%; p < 0.01), and PI (1.23 ± 0.22% vs. 3.46 ± 0.18%; p < 0.01), and higher effective orifice area (1.51 ± 0.08 cm(2) vs. 1.35 ± 0.02 cm(2); p < 0.01) at the cost of lower pullout forces (5.54 ± 0.20 N vs. 7.09 ± 0.49 N; p < 0.01). For both CoreValve sizes, optimal deployment was observed at the normal position. The 26-mm CoreValve, when compared with the 23-mm CoreValve and 23-mm SAPIEN, had a lower TVPG (7.76 ± 0.14 mm Hg vs. 10.27 ± 0.18 mm Hg vs. 9.31 ± 0.22 mm Hg; p < 0.01) and higher effective orifice area (1.66 ± 0.05 cm(2) vs. 1.44 ± 0.05 cm(2) vs. 1.51 ± 0.08 cm(2); p < 0.01), RF (4.79 ± 0.67% vs. 1.98 ± 0.36% vs. 0.95 ± 1.68%; p < 0.01), PI (29.13 ± 0.22% vs. 6.57 ± 0.14% vs. 1.23 ± 0.22%; p < 0.01), and pullout forces (10.65 ± 0.66 N vs. 5.35 ± 0.18 N vs. 5.54 ± 0.20 N; p < 0.01). CONCLUSIONS: The optimal deployment location for VIV in a 23 PERIMOUNT surgical bioprosthesis was at a +6 mm supra-annular position for a 23-mm SAPIEN valve and at the normal position for both the 23-mm and 26-mm CoreValves. The 26-mm CoreValve had lower gradients, but higher RF and PI than the 23-mm CoreValve and the 23-mm SAPIEN. In their optimal positions, all valves resulted in hemodynamics consistent with the definitions of Valve Academic Research Consortium-2 procedural success. Long-term studies are needed to understand the clinical impact of these hemodynamic performance differences in patients who undergo VIV transcatheter aortic valve replacement.

Role of Mitral Annulus Diastolic Geometry on Intraventricular Filling Dynamics.

The mitral valve (MV) is a bileaflet valve positioned between the left atrium and ventricle of the heart. The annulus of the MV has been observed to undergo geometric changes during the cardiac cycle, transforming from a saddle D-shape during systole to a flat (and less eccentric) D-shape during diastole. Prosthetic MV devices, including heart valves and annuloplasty rings, are designed based on these two configurations, with the circular design of some prosthetic heart valves (PHVs) being an approximation of the less eccentric, flat D-shape. Characterizing the effects of these geometrical variations on the filling efficiency of the left ventricle (LV) is required to understand why the flat D-shaped annulus is observed in the native MV during diastole in addition to optimizing the design of prosthetic devices. We hypothesize that the D-shaped annulus reduces energy loss during ventricular filling. An experimental left heart simulator (LHS) consisting of a flexible-walled LV physical model was used to characterize the filling efficiency of the two mitral annular geometries. The strength of the dominant vortical structure formed and the energy dissipation rate (EDR) of the measured fields, during the diastolic period of the cardiac cycle, were used as metrics to quantify the filling efficiency. Our results indicated that the O-shaped annulus generates a stronger (25% relative to the D-shaped annulus) vortical structure than that of the D-shaped annulus. It was also found that the O-shaped annulus resulted in higher EDR values throughout the diastolic period of the cardiac cycle. The results support the hypothesis that a D-shaped mitral annulus reduces dissipative energy losses in ventricular filling during diastole and in turn suggests that a symmetric stent design does not provide lower filling efficiency than an equivalent asymmetric design.

Cardiovascular magnetic resonance compatible physical model of the left ventricle for multi-modality characterization of wall motion and hemodynamics.

BACKGROUND: The development of clinically applicable fluid-structure interaction (FSI) models of the left heart is inherently challenging when using in vivo cardiovascular magnetic resonance (CMR) data for validation, due to the lack of a well-controlled system where detailed measurements of the ventricular wall motion and flow field are available a priori. The purpose of this study was to (a) develop a clinically relevant, CMR-compatible left heart physical model; and (b) compare the left ventricular (LV) volume reconstructions and hemodynamic data obtained using CMR to laboratory-based experimental modalities. METHODS: The LV was constructed from optically clear flexible silicone rubber. The geometry was based off a healthy patient's LV geometry during peak systole. The LV phantom was attached to a left heart simulator consisting of an aorta, atrium, and systemic resistance and compliance elements. Experiments were conducted for heart rate of 70 bpm. Wall motion measurements were obtained using high speed stereo-photogrammetry (SP) and cine-CMR, while flow field measurements were obtained using digital particle image velocimetry (DPIV) and phase-contrast magnetic resonance (PC-CMR). RESULTS: The model reproduced physiologically accurate hemodynamics (aortic pressure = 120/80 mmHg; cardiac output = 3.5 L/min). DPIV and PC-CMR results of the center plane flow within the ventricle matched, both qualitatively and quantitatively, with flow from the atrium into the LV having a velocity of about 1.15 m/s for both modalities. The normalized LV volume through the cardiac cycle computed from CMR data matched closely to that from SP. The mean difference between CMR and SP was 5.5 ± 3.7%. CONCLUSIONS: The model presented here can thus be used for the purposes of: (a) acquiring CMR data for validation of FSI simulations, (b) determining accuracy of cine-CMR reconstruction methods, and