Patient-specific image-based computer simulation for theprediction of valve morphology and calcium displacement after TAVI with the Medtronic CoreValve and the Edwards SAPIEN valve

AIMS: Our aim was to validate patient-specific software integrating baseline anatomy and biomechanical properties of both the aortic root and valve for the prediction of valve morphology and aortic leaflet calcium displacement after TAVI. METHODS AND RESULTS: Finite element computer modelling was performed in 39 patients treated with a Medtronic CoreValve System (MCS; n=33) or an Edwards SAPIEN XT (ESV; n=6). Quantitative axial frame morphology at inflow (MCS, ESV) and nadir, coaptation and commissures (MCS) was compared between multislice computed tomography (MSCT) post TAVI and a computer model as well as displacement of the aortic leaflet calcifications, quantified by the distance between the coronary ostium and the closest calcium nodule. Bland-Altman analysis revealed a strong correlation between the observed (MSCT) and predicted frame dimensions, although small differences were detected for, e.g., Dmin at the inflow (mean±SD MSCT vs. MODEL: 21.6±2.4 mm vs. 22.0±2.4 mm; difference±SD: -0.4±1.3 mm, p<0.05) and Dmax (25.6±2.7 mm vs. 26.2±2.7 mm; difference±SD: -0.6±1.0 mm, p<0.01). The observed and predicted calcium displacements were highly correlated for the left and right coronary ostia (R2=0.67 and R2=0.71, respectively p<0.001). CONCLUSIONS: Dedicated software allows accurate prediction of frame morphology and calcium displacement after valve implantation, which may help to improve outcome

Optimization of a transcatheter heart valve frame using patient-specific computer simulation

Purpose This study proposes a new framework to optimize the design of a transcatheter aortic valve through patient-specific finite element and fluid dynamics simulation. Methods Two geometrical parameters of the frame, the diameter at ventricular inflow and the height of the first row of cells, were examined using the central composite design. The effect of those parameters on postoperative complications was investigated by response surface methodology, and a Nonlinear Programming by Quadratic Lagrangian algorithm was used in the optimization. Optimal and initial devices were then compared in 12 patients. The comparison was made in terms of device performance [i.e., reduced contact pressure on the atrioventricular conduction system and paravalvular aortic regurgitation (AR)]. Results Results suggest that large diameters and high cells favor higher anchoring of the device within the aortic root reducing the contact pressure and favor a better apposition of the device to the aortic root preventing AR. Compared to the initial device, the optimal device resulted in almost threefold lower predicted contact pressure and limited AR in all patients. Conclusions In conclusion, patient-specific modelling and simulation could help to evaluate device performance prior to the actual first-in-human clinical study and, combined with device optimization, could help to develop better devices in a shorter period

Patient-specific Computer Simulation: An Emerging Technology for Guiding the Transcatheter Treatment of Patients with Bicuspid Aortic Valve.

Transcatheter aortic valve implantation (TAVI) is increasingly being used to treat younger, lower-risk patients, many of whom have bicuspid aortic valve (BAV). As TAVI begins to enter these younger patient cohorts, it is critical that clinical outcomes from TAVI in BAV are matched to those achieved by surgery. Therefore, the identification of patients who, on an anatomical basis, may not be suitable for TAVI, would be desirable. Furthermore, clinical outcomes of TAVI in BAV might be improved through improved transcatheter heart valve sizing and positioning. One potential solution to these challenges is patient-specific computer simulation. This review presents the methodology and clinical evidence surrounding patient-specific computer simulation of TAVI in BAV

Finite Element Analysis to Study Percutaneous Heart Valves

Communications engineering / telecommunication

Energetic and Hemodynamic Characteristics of Paravalvular Leak Following Transcatheter Aortic Valve Replacement

Transcatheter aortic valve replacement (TAVR) has emerged as an alternative treatment for inoperable and high risk patients with severe symptomatic aortic stenosis. TAVR short and medium term results are very promising, however paravalvular leak (PVL) post-TAVR still represents a significant complication. PVL post-TAVR is shown to be an independent predictor of short-term and long-term mortality. Despite, its importance and prevalence, with a wide range of reported incidences, only few studies addressed the PVL after TAVR. In the present study, first, the mathematical lumped parameter model is used to model the simplified circulatory system in presence of PVL and to evaluate the performance of TAVR by computing the variation of the left ventricle stroke work (LVSW) under several pre-TAVR and post-TAVR conditions. Results show that in a large majority of cases, TAVR significantly reduced LVSW. However, in cases with pre-existing aortic stenosis conditions with trace/mild aortic regurgitation, it did not significantly reduce LVSW or even led to an increase. Second, a three-dimensional (3D) computational fluid dynamics (CFD) simulation is performed in order to investigate the effect of PVL on the diastolic flow-field characteristics post-TAVR. Results show that PVL leads to significant disturbances in blood flow, which characterized by high speed jets, coherent structures and markedly elevated shear stress on both sides of the implanted aortic leaflets, which could promote a more rapid degeneration of the valve leaflets. Results could be useful in understating the hemodynamics of PVL post-TAVR and estimating some important parameters, which could not be obtained during the medical assessment (e.g. wall shear stress). Also, they could be a help in the process of choosing the appropriate valve for TAVR procedure, based on comparing the pre and post TAVR different scenarios

On the Modeling of Transcatheter Therapies for the Aortic and Mitral Valves: A Review

Transcatheter aortic valve replacement (TAVR) has become a milestone for the management of aortic stenosis in a growing number of patients who are unfavorable candidates for surgery. With the new generation of transcatheter heart valves (THV), the feasibility of transcatheter mitral valve replacement (TMVR) for degenerated mitral bioprostheses and failed annuloplasty rings has been demonstrated. In this setting, computational simulations are modernizing the preoperative planning of transcatheter heart valve interventions by predicting the outcome of the bioprosthesis interaction with the human host in a patient-specific fashion. However, computational modeling needs to carry out increasingly challenging levels including the verification and validation to obtain accurate and realistic predictions. This review aims to provide an overall assessment of the recent advances in computational modeling for TAVR and TMVR as well as gaps in the knowledge limiting model credibility and reliability

Stents for transcatheter aortic valve replacement

Rheumatic heart disease (RHD) is the leading cause of aortic valve disease in the world. Surgery to repair or replace the diseased valves is the only means to save a patient's life once the disease becomes symptomatic. Transcatheter aortic valve replacement (TAVR) has revolutionised the treatment of age-related degenerative aortic valve disease, but is currently not suitable for the majority of RHD sufferers due to the rapid degeneration of flexible leaflet valves in younger patients, contraindications of commercial devices to regurgitant or non-calcific aortic valve disease, and also due to resource or funding limitations. The current research project aimed to develop and test novel compressible balloon-expandable stents suitable for patients with symptomatic rheumatic aortic valve disease, and which would allow for a percutaneous polymeric valve to be manufactured, be crimped onto balloon-based devices, and be expanded into a compliant or non-calcific native aortic valve. Several stent concepts were developed and evaluated using Finite Element Analysis (FEA) and two favoured concepts were selected for more complex FEA, in which the balloon was simulated using an Ogden material model, and rigorous testing. The stent material, a nickel-cobalt-chromium alloy, was modelled as an isotropic elasto-plastic material with isotropic hardening. The novel stent designs incorporated a native leaflet-mimicking crown shape for continuous leaflet attachment and mechanisms to anchor the stented valve within compliant aortic roots. The first of the favoured designs provided tactile location during delivery and anchored using self-expanding arms on a balloon-expandable frame of the same material ("self-locating stents"). The second design anchored using arms that protruded during deployment as a consequence of plastic deformation incurred during crimping ("expanding arm stents"). Prototypes were successfully manufactured through laser cutting and electropolishing and showed good surface quality. In vitro testing included determination of crimping and expansion behaviour and measurement of mechanical properties such as resistance to migration in the anatomy. Valve performance was evaluated through in vitro haemodynamics in a pulse duplicator and durability was tested in a high-cycle fatigue tester. Simulated use testing was performed using cadaveric animal hearts. Finally, valves were also implanted into the aortic valve position of pigs (in acute termination experiments) through a transapical approach in order to verify valve deployment behaviour and function in vivo, and determine the stent's ability to anchor in the native anatomy. Stents could be crimped to diameters below 6mm and deployed using commercial balloons and proprietary non-occlusive deployment devices. FEA simulations of stent crimping and deployment matched experimental behaviour well and provide a tool to optimise stent performance. Peak Von Mises stresses during deployment (1437 MPa and 1633 MPa for self-locating and expanding arm stents, respectively) were comparable to a "zig-zag" stent simulated for control purposes (1650 MPa). Radial strength, evaluated for expanding arm stents, was lower than the Control stent (116 N vs. 347 N). This design, although predicted to be safe under fatigue loading, had a lower fatigue safety factor than the Control stent. Stents resisted migration to forces of at least 22 N, which is four times greater than physiological loading on the valves. Polymeric valves incorporating the stents were constructed and demonstrated good in vitro haemodynamic performance (Effective Orifice Areas ≥2.0cm², ΔP<9 mmHg, regurgitation <6%) and durability of over 400 million cycles. Designs functioned as intended in simulated use tests. Valves constructed using self-locating stents could be successfully deployed without rapid pacing in eight of nine pigs, and valve position was correct in seven of these. Valves of expanding arm stents remained anchored in six of eight attempted implants in pigs. This study has demonstrated proof of concept for a novel balloon-expandable stent for a polymeric transcatheter heart valve that is capable of anchoring in a compliant native aortic valve

Computed Tomography-Derived 3D Modeling to Guide Sizing and Planning of Transcatheter Mitral Valve Interventions

A plethora of catheter-based strategies have been developed to treat mitral valve disease. Evolving 3-dimensional (3D) multidetector computed tomography (MDCT) technology can accurately reconstruct the mitral valve by means of 3-dimensional computational modeling (3DCM) to allow virtual implantation of catheter-based devices. 3D printing complements computational modeling and offers implanting physician teams the opportunity to evaluate devices in life-size replicas of patient-specific cardiac anatomy. MDCT-derived 3D computational and 3D-printed modeling provides unprecedented insights to facilitate hands-on procedural planning, device training, and retrospective procedural evaluation. This overview summarizes current concepts and provides insight into the application of MDCT-derived 3DCM and 3D printing for the planning of transcatheter mitral valve replacement and closure of paravalvular leaks. Additionally, future directions in the development of 3DCM will be discussed

Transcatheter Mitral Valve Replacement: Structural and Hemodynamic Analysis

Transcatheter mitral valve replacement (TMVR) is being developed to become a substitute therapy for surgery in prohibitive or high surgical risk patients to treat severe mitral regurgitation. A limited number of TMVR systems are under clinical evaluation. However, transcatheter mitral valve (TMV) long-term durability and hemodynamic performance is not known. TMV durability and hemodynamics must match with that of surgical bioprostheses for potential commercialization of TMVR. Experimental and computational approaches were used to find the leaflets’ three-dimensional anisotropic mechanical properties in a transcatheter Edwards SAPIEN 3 valve and a surgical Carpentier-Edwards PERIMOUNT Magna mitral valve and finite element (FE) simulations were conducted to obtain the stress distribution on both valves. Moreover, to visualize the flow field within the left heart, steady-state computational fluid dynamics (CFD) simulations were run. The FE simulations demonstrated that in a cardiac cycle, at peak systole, the highest stress value in the two bioprostheses was 4.75 and 16 MPa for the surgical and transcatheter heart valve, respectively. After studying the leaflet stress distributions and flow field, long-term durability may potentially be different between the two models. The results of CFD simulations could potentially show that TMVs with supra-annular positioning have a higher risk of leaflet thrombosis as opposed to the intra-annular position