Research Publications

Subclinical leaflet thrombosis is a silent phenomenon commonly observed following transcatheter aortic valve implantation. Leaflet thrombosis is associated with ischaemic complications and structural valve deterioration. Prior studies have shown that blood stasis in neo-sinus contributes to the initiation and growth of subclinical leaflet thrombosis. This study aimed to quantify the temporal and spatial characteristics of the flow field from a fundamental perspective.

METHODS

In vitro experimental analysis and fluid–solid interaction simulations were employed to characterize the flow field of a transcatheter aortic valve (TAV) with an intra-annular design in a pulse duplicator. Blood residence time (BRT) and flow-induced viscous shear stress were measured in the neo-sinus and on the surface of TAV leaflets.

RESULTS

Temporal and spatial velocity variations were observed in neo-sinus, indicating that the flow is time dependent and fully three-dimensional. The degree of blood stasis in the neo-sinus (bulk fluid) and on the surface of the TAV leaflets highly depends on the local flow characteristics. Regional flow variation in the neo-sinus resulted in substantial variations in BRT magnitude in the neo-sinus and on the surface of the TAV leaflet. Areas with a high degree of blood stasis were observed near the fixed boundary edge of the leaflets.

CONCLUSIONS

The study indicated that leaflet motion is a primary driver of flow in neo-sinus. Considering the substantial variations in BRT magnitude in the neo-sinus (bulk fluid), blood stasis should be quantified locally on the surface of foreign (valve) materials to avoid errors in forecasting the risk of subclinical leaflet thrombosis in patients undergoing transcatheter aortic valve implantation.

Subclinical leaflet thrombosis has been increasingly observed in patients undergoing transcatheter aortic valve replacement. Intra-annular transcatheter aortic valves (TAVs) have a larger neo-sinus volume than supra-annular devices and are potentially at a higher risk of hypoattenuated leaflet thickening (HALT). However, clinical data from randomized clinical trials have shown that approximately one-third of patients undergoing TAVR with intra- or supra-annular devices develop HALT in 1 year. The findings point to the potential role of leaflet design in developing HALT. The study aimed to systematically investigate leaflet kinematics of a supra-annular TAV, Medtronic CoreValve, and determine regions of blood stasis. Fluid–solid interaction simulations demonstrated the limited movement of CoreValve leaflets in the lower belly region that created regions of blood stasis on the surface of the leaflets. The findings provide insights into potential improvements in leaflet design in the next generation of TAVs to reduce the risk of HALT and leaflet immobility.

Subclinical leaflet thrombosis has been increasingly recognized following transcatheter aortic valve replacement (TAVR). Determining the risk factors is vital in preventing clinical leaflet thrombosis and ensuring long-term value durability. Clinical data have indicated that regional stent under-expansion of transcatheter aortic valves (TAVs), particularly self-expanding devices, may be associated with an increased risk of subclinical leaflet thrombosis. This study aimed to determine the effects of regional TAV frame under-expansion on leaflet kinematics, leaflet structural characteristics, and explore its impact on the likelihood of leaflet thrombosis. In this study, mild and moderate regional frame under-expansion of a 26-mm CoreValve were examined using experimental testing and computational simulations. The results indicated that regional TAV frame under-expansion impairs leaflet kinematics and reduces the range of motion in leaflets with an angle less than 120°. The reduced range of motion can increase blood stasis on the surface of the TAV leaflets. The results also demonstrated that regional frame under-expansion induced localized high-stress regions in the leaflets close to the fixed boundary edge. The increased mechanical stress can lead to accelerated tissue degeneration. The study improves our understanding of the effects of regional stent under-expansion in TAVR. Post-procedural balloon dilatation of self-expanding TAVs can potentially be advantageous in reducing leaflet distortion and normalizing leaflet stress distribution. Large-scale, prospective, and well-controlled studies are needed to further investigate regional TAV frame under-expansion effects on subclinical leaflet thrombosis and long-term valve durability.

Leaflet thrombosis of bioprosthetic aortic valves is an increasingly recognised complication. Subclinical leaflet thrombosis is more commonly observed following transcatheter aortic valve implantation (TAVI) and valve-in-valve (ViV) procedures than in surgical aortic valve replacement. Anticoagulation therapy with warfarin, as compared with dual antiplatelet therapy, was associated with a decrease in the incidence of reduced leaflet motion in these patients. However, bleeding is a complication of anticoagulation therapy, and recurrence of reduced leaflet motion has been observed following discontinuation of the anticoagulation therapy. Therefore, minimising the thrombogenicity of transcatheter aortic valves (TAVs) besides the pharmacological prevention methods is essential to ensure optimal long-term valve function. We have previously investigated the underlying flow-mediated mechanism that facilitates thrombus formation on TAV leaflets by computational modelling. As another step towards minimising the thrombogenicity of TAVs, the present work aims to study the effects of transcatheter laceration of degenerated bioprosthetic valve leaflets, also known as the BASILICA (bioprosthetic or native aortic scallop intentional laceration to prevent iatrogenic coronary artery obstruction) procedure, on the likelihood of leaflet thrombosis following ViV procedures. Although BASILICA was primarily developed to prevent coronary artery obstruction, the present work aims to study the role of BASILICA in diminishing the risk of leaflet thrombosis by increasing blood washout (that is, decreasing blood stasis) on the surface of the TAV leaflets.

Transcatheter heart valve (THV) replacement is an advancing field, with various valve designs incorporating features like flexible frames to improve valve hemodynamics, durability, and patient outcomes. Leaflet pinwheeling, a common metric, is thought to negatively impact long-term durability. This study investigates the pinwheeling index and its correlation with stress distribution across different THV designs. Three THV designs were created using an optimization framework, each with a nominal size of 26-mm and varying leaflet coaptation heights of 10-mm, 13-mm, and 16-mm. Each valve design was evaluated under two conditions: one with a rigid frame and one with a flexible frame. The valves were implanted with a 90 % area expansion ratio, and their performance was assessed by examining key mechanical parameters, including the pinwheeling index and maximum in-plane principal stress under a diastolic loading condition. At a coaptation height of 10-mm, the pinwheeling index was 0 % for both frame types. At 13-mm, the rigid frame maintained a low index of 2 %, while the flexible frame increased slightly to 4 %. At 16-mm, the index rose for both frames, with the rigid frame at 7 % and the flexible frame at 10 %. The study found that leaflet stress was unrelated to the pinwheeling index. While flexible frames may reduce stress and improve long-term durability, they increase the pinwheeling index. Therefore, the traditional pinwheeling index may not reliably predict accelerated leaflet degeneration across different valve designs in comparative analyses. A comprehensive evaluation incorporating computational modeling, digital image correlation, and experimental validation is crucial for preclinical assessments.

Bicuspid aortic valve is a congenital cardiac anomaly and common etiology of aortic stenosis. Given the positive outcomes of transcatheter aortic valve replacement (TAVR) in low-risk patients, TAVR will become more prevalent in the future in the treatment of severe bicuspid valve stenosis. However, asymmetrical bicuspid valve anatomy and calcification can prevent the circular and complete expansion of transcatheter aortic valves (TAVs). In previous studies, examining the impact of elliptical TAV deployment on leaflet stress distribution, asymmetric expansion of balloon-expandable intra-annular devices was studied up to an ellipticity index (long/short TAV diameter) of 1.4. However, such a high degree of eccentricity has not been observed in clinical studies with balloon-expandable devices. High degrees of stent eccentricity have been observed in self-expanding TAVs, such as CoreValve. However, CoreValve is a supra-annular device, and it was not clear if eccentric and incomplete stent deployment at the annulus would alter leaflet stress and strain distributions. This study aimed to assess the effects of eccentric and incomplete stent deployment of CoreValves in bicuspid aortic valves and compare the results to that of SAPIEN 3. Leaflet stress distribution and leaflet kinematics of 26-mm CoreValve and 26-mm SAPIEN 3 devices in bicuspid valves were obtained in a range that was observed in previous clinical studies. The results indicated that elliptical and incomplete stent deployment of TAVs increase leaflet stress and impair leaflet kinematics. The changes were more pronounced in CoreValve than SAPIEN 3. Increased leaflet stress can reduce long-term valve durability, and impaired leaflet kinematics can potentially increase blood stasis on the TAV leaflets. The study provides complementary insights into the mechanics of TAVs in bicuspid aortic valves.

Transcatheter aortic valve replacement (TAVR) is a safe and effective treatment option for patients deemed at high and intermediate risk for surgical aortic valve replacement. Similar to surgical aortic valves (SAVs), transcatheter aortic valves (TAVs) undergo calcification and mechanical wear over time. However, to date, there have been limited publications on the long-term durability of TAV devices. To assess longevity and mechanical strength of TAVs in comparison to surgical bioprosthetic valves, three-dimensional deformation analysis and strain measurement of the leaflets become an inevitable part of the evaluation. The goal of this study was to measure and compare leaflet displacement and strain of two commonly used TAVs in a side-by-side comparison with a commonly used SAV using a high-resolution digital image correlation (DIC) system. 26-mm Edwards SAPIEN 3, 26-mm Medtronic CoreValve, and 25-mm Carpentier-Edwards PERIMOUNT Magna surgical bioprosthesis were examined in a custom-made valve testing apparatus. A time-varying, spatially uniform pressure was applied to the leaflets at different loading rates. GOM ARAMIS software was used to map leaflet displacement and strain fields during loading and unloading. High displacement regions were found to be at the leaflet belly region of the three bioprosthetic valves. In addition, the frame of the surgical bioprosthesis was found to be remarkably flexible, in contrary to CoreValve and SAPIEN 3 in which the stent was nearly rigid under a similar loading condition. The experimental DIC measurements can be used to characterize the anisotropic material behavior of the bioprosthetic heart valve leaflets and validate heart valve computational simulations.

Purpose

Alcohol septal ablation (ASA) has become a minimally invasive alternative to septal myectomy for treating left ventricular outflow tract (LVOT) obstructions. ASA has gained popularity, especially among patients undergoing transcatheter mitral valve replacement (TMVR). This study aimed to determine the effect of ASA on the mechanical properties of myocardial tissue.

Methods

Twenty-four square samples were excised from the septal regions of fresh-frozen swine hearts. Mechanical testing was conducted using a biaxial tester. Half of the samples underwent 3-minute ablation, while the other half underwent 5-minute ablation.

Results

All samples exhibited a nonlinear response to strain in the fiber and cross-fiber directions. After 3 min of ablation, the mean force required to achieve 20% displacement increased from 182.08-mN to 347.42-mN (true stress from 11.0-KPa to 24.1-KPa) in the fiber direction and from 66.83-mN to 110.75-mN (true stress from 4.3-KPa to 8.2-KPa) in the cross-fiber direction. Following 5 min of ablation, mean force values rose from 178.0-mN to 452.8-mN (true stress from 11.0-KPa to 32.4-KPa) in the fiber direction, and from 70.0-mN to 154.8-mN (true stress from 4.8-KPa to 12.0-KPa) in the cross-fiber direction. All changes were statistically significant (p ≤ 0.002). Histological analysis also revealed that alcohol ablation progressively disrupted myocardial architecture.

Conclusion

This study demonstrates that ASA significantly alters the passive mechanical properties of the myocardium, increasing tissue stiffness in the septal region over the short term. The extent of stiffening is directly proportional to the duration of ablation, with longer ablation times causing greater stiffness, necessitating careful selection of ablation time before TMVR procedures.

Cardiovascular tissues exhibit complex mechanical behaviors that are nonlinear, anisotropic, and spatially heterogeneous. These local and regional variations play a critical role in disease initiation, progression, and treatment outcomes, yet conventional approaches often rely on specimen-averaged properties that overlook this heterogeneity. This review highlights recent advances in local mechanical characterization, spanning experimental methods, imaging-based assessments, and computational strategies. Traditional mechanical tests, such as uniaxial, biaxial, and indentation methods, remain foundational but assume uniform material properties. Surface-based techniques, particularly digital image correlation, now enable high-resolution full-field strain mapping in vitro and even intraoperatively, while volumetric approaches—including ultrasound, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), and Optical Coherence Tomography (OCT)—extend characterization to through-thickness and into in vivo settings. Digital volume correlation (DVC) further enhances these modalities by extracting three-dimensional internal displacement fields, though its use in cardiovascular tissues is still emerging. To translate these data into clinically relevant metrics, inverse methods such as the Virtual Fields Method (VFM) and inverse finite element analysis (iFEA) are used to estimate region-specific constitutive parameters. Emerging machine learning and physics-informed frameworks further accelerate model selection, parameter identification, and uncertainty quantification. Despite significant progress, major challenges remain in image quality in dynamic in vivo environments, uncertain boundary conditions, computational costs, and the lack of standardized protocols. Future progress will rely on integrating multimodal imaging, robust inverse modeling, and physics-informed machine learning into reproducible pipelines capable of generating patient-specific mechanical maps. Ultimately, local characterization holds the potential to transform risk prediction, medical device optimization, and personalized treatment planning in cardiovascular medicine.

Pulmonary valve dysfunction is common in congenital heart disease, often leading to interventions like right ventricular outflow tract reconstruction. Transcatheter pulmonary valve replacement (TPVR) has emerged as a successful alternative to surgery, showcasing promising outcomes for managing postoperative RVOT complications. The study aimed to compare two bioprosthetic valves—Carpentier Edwards Perimount Magna Ease surgical valve and Edwards SAPIEN 3 transcatheter valve—originally designed for aortic use but adapted for pulmonary applications. The hemodynamic characteristics of a 26-mm SAPIEN 3 and a 25-mm Magna Ease were assessed in a pulse duplicator under both pulmonary and aortic conditions. Furthermore, detailed structural analyses of the leaflets were conducted using computational simulations under these conditions. The results highlighted significant differences in the hydrodynamic and structural characteristics of these two bioprosthetic valves when exposed to pulmonary versus aortic conditions. The study enhances our understanding of the biomechanics involved in surgical and transcatheter pulmonary valve replacement.

Background

Redo-transcatheter aortic valve replacement (TAVR) is a promising treatment for transcatheter aortic valve degeneration, becoming increasingly relevant with an aging population. In redo-TAVR, the leaflets of the initial (index) transcatheter aortic valve (TAV) are displaced vertically when the second TAV is implanted, creating a cylindrical cage that can impair coronary cannulation and flow. Preventing coronary obstruction and maintaining coronary access is essential, especially in young and low-risk patients undergoing TAVR. This study aimed to develop a new leaflet modification strategy using laser ablation to prevent coronary obstruction and facilitate coronary access after repeat TAVR.

Methods

To evaluate the feasibility of the leaflet modification technique using laser ablation, the initial phase of this study involved applying a medical-grade ultraviolet laser for ablation through pericardial tissue. Following this intervention, computational fluid dynamics simulations were utilized to assess the efficacy of the resulting perforations in promoting coronary flow. These simulations played a crucial role in understanding the impact of the modifications on blood flow patterns, ensuring these changes would facilitate the restoration of coronary circulation.

Results

Laser ablation of pericardium leaflets was successful, demonstrating the feasibility of creating openings in the TAV leaflets. Flow simulation results show that ablation of index valve leaflets can effectively mitigate the flow obstruction caused by sinus sequestration in redo-TAVR, with the extent of restoration dependent on the number and location of the ablated openings.

Conclusions

Laser ablation could be a viable method for leaflet modification in redo-TAVR, serving as a new tool in interventional procedures.