Aortic valve leaflet mechanical properties facilitate diastolic valve function

This work was concerned with the numerical simulation of the behaviour of aortic valves whose material can be modelled as non-linear elastic anisotropic. Linear elastic models for the valve leaflets with parameters used in previous studies were compared with hyperelastic models, incorporating leaflet anisotropy with pronounced stiffness in the circumferential direction through a transverse isotropic model. The parameters for the hyperelastic models were obtained from fits to results of orthogonal uniaxial tensile tests on porcine aortic valve leaflets. The computational results indicated the significant impact of transverse isotropy and hyperelastic effects on leaflet mechanics; in particular, increased coaptation with peak values of stress and strain in the elastic limit. The alignment of maximum principal stresses in all models follows approximately the coarse collagen fibre distribution found in aortic valve leaflets. The non-linear elastic leaflets also demonstrated more evenly distributed stress and strain which appears relevant to long-term scaffold stability and mechanotransduction.     

Impact of calcific aortic valve disease on valve mechanics

Biomechanics and Modeling in Mechanobiology - The aortic valve is a highly dynamic structure characterized by a transvalvular flow that is unsteady, pulsatile, and characterized by episodes of...     

Prosthetic valve endocarditis.

During 1965 to 1982, 32 episodes of infective endocarditis on prosthetic valves in 30 patients were treated at this hospital. In early endocarditis (presenting within four months of operation) staphylococci were the organisms most commonly responsible. Early endocarditis appears to be declining in incidence and is largely preventable; sternal sepsis was the main predisposing factor, requiring urgent and effective treatment. Streptococci were the most common organisms in late onset disease, but as with natural valve endocarditis a wide range or organisms was responsible. All but one of the patients with early onset disease were treated conservatively, but mortality was high; prompt surgical replacement of infected prostheses is probably indicated in such patients. Medical management was effective in most patients with late onset disease, and for them early surgical intervention may not be justified.     

Transcatheter aortic valve implantation

There has been significant improvement in device designs, operative techniques, and early clinical outcomes in <5 years. Presently, there are two catheter-based bioprostheses (balloon expandable or self-expandable), which have been widely used in humans and are undergoing clinical investigations. Three approaches, including transvenous, transarterial, and transapical have been used for delivery of the catheter-based bioprostheses, and transarterial and transapical approaches have been adopted by cardiologists and cardiac surgeons worldwide. The most recent clinical results have been very encouraging and promising. With experience, 30-day operative mortality with either balloon-expandable or self-expandable bioprosthesis was reduced significantly to approximately 10% in high-risk patients. In vivo long-term durability of catheter-based bioprostheses remains unknown, and presently transcatheter procedure is limited to the cohort of high-risk patients. Expanding this new technology to low-risk patients should be done with extreme caution because conventional aortic valve replacement still provides the best long-term outcome with minimal operative mortality and morbidity in low-risk patients. Ongoing clinical trials will address many unanswered questions, such as patient selection, long-term in vivo durability, preoperative assessment, and the role of the procedures in management of valvular diseases.     

Bioprosthetic mitral valve thrombosis

Netherlands Heart Journal -     

Multidisciplinary decision-making in mitral valve disease: the mitral valve heart team

Background

Although decision-making using the heart-team approach is apparently intuitive and has a class I recommendation in most recent guidelines, supportive data is still lacking. The current study aims to demonstrate the individualised clinical pathway for mitral valve disease patients and to evaluate the outcome of all patients referred to the dedicated mitral valve heart team.

Methods

All patients who were evaluated for mitral valve pathology with or without concomitant cardiac disease between 1 January 2016 and 31 December 2016 were prospectively followed and included. Patients were evaluated, and a treatment strategy was determined by the dedicated mitral valve heart team.

Results

One hundred and fifty-eight patients were included; 67 patients were treated surgically (isolated and concomitant surgery), 20 by transcatheter interventions and 71 conservatively. Surgically treated patients had a higher 30-day mortality rate (4.4%), which decreased when specified to a dedicated surgeon (1.7%) and in primary, elective cases (0%). This was also observed for major adverse events within 30 days. Residual mitral regurgitation >grade 2 was more frequent in the catheter-based intervention group (23.5%) compared to the surgical group (4.8%).

Conclusion

In conclusion, the implementation of a multidisciplinary heart team for mitral valve disease is a valuable approach for the selection of patients for different treatment modalities. Our research group will focus on a future comparative study using historical cohorts to prove the potential superiority of the dedicated multidisciplinary heart-team approach.

     

Simulated elliptical bioprosthetic valve deformation: Implications for asymmetric transcatheter valve deployment

The asymmetric, elliptical shape of a transcatheter aortic valve (TAV), after implantation into a calcified aortic root, has been clinically observed. However, the impact of elliptical TAV configuration on TAV leaflet stress and strain distribution and valve regurgitation is largely unknown. In this study, we developed computational models of elliptical TAVs based on a thin pericardial bioprosthetic valve model recently developed. Finite element and computational fluid dynamics simulations were performed to investigate TAV leaflet structural deformation and central backflow leakage, and compared with those of a nominal symmetric TAV. From the results, we found that for a distorted TAV with an elliptical eccentricity of 0.68, the peak stress increased significantly by 143% compared with the nominal circular TAV. When the eccentricity of an elliptical TAV was larger than 0.5, a central backflow leakage was likely to occur. Also, deployment of a TAV with a major calcified region perpendicular to leaflet coaptation line was likely to cause a larger valve leakage. In conclusion, the computational models of elliptical TAVs developed in this study could improve our understanding of the biomechanics involved in a TAV with an elliptical configuration and facilitate optimal design of next-generation TAV devices.     

The cardiac valve interstitial cell

Cardiac valve interstitial cells (ICs) are a heterogeneous and dynamic population of specific cell types that have many unique characteristics. They are responsible for maintaining the extracellular scaffold that provides the mechanical characteristics vital for sustaining the unique dynamic behaviour of the valve. A number of cellular phenotypes can be distinguished: some are sparsely arranged throughout the valve leaflets, whilst others are arranged in thin bundles. These cells express molecular markers similar to those of skeletal, cardiac and smooth muscle cells (SMCs) and in particular, many ICs express smooth muscle (SM) alpha-actin, a marker of myofibroblasts. In this respect, these cells exhibit a profile unlike skin fibroblasts, which may allude to their role in valve function.