Computational virtual evaluation of the effect of annuloplasty ring shape

Mitral valve surgery assisted by virtual and augmented reality: Cardiac surgery at the front of innovation

BACKGROUND

Given the variety in mitral valve (MV) pathology and associated surgical techniques, extended reality (XR) holds great potential to assist MV surgeons. This review aims to systematically evaluate the currently available evidence investigating the use of XR and associated technologies in MV surgery.

METHODS

A systematic database search was conducted of original articles and case reports that explored the use of XR and MV surgery in EMBASE, MEDLINE, Cochrane database and Google Scholar, from inception to February 2022.

RESULTS

Our search yielded 171 articles, of which 15 studies were included in this review, featuring 328 patients. Two main areas of application were identified: (i) pre-operative planning and (ii) predicting post-operative outcomes. The articles reporting outcomes relating to pre-operative planning were further categorised as exploring themes relevant to (i) mitral annular assessment; (ii) training; (iii) evaluation of surgical technique; (iv) surgical approach or plan and (v) selecting ring size or type. Preoperatively, XR has been shown to evaluate mitral annular pathology more accurately than echocardiography, informing the surgeon about the optimal surgical technique, approach and plan for a particular patient's MV pathology. Furthermore, XR could simulate and aid ring size/type selection for MV annuloplasty, creating a personalized surgical plan. Additionally, XR could estimate the postoperative MV biomechanical and physiological characteristics, predicting and pre-empting post-operative complications.

CONCLUSION

XR demonstrated promising applications for assisting MV surgery, enhancing outcomes and patient-centred care, nevertheless, there remain the need for randomized studies to ascertain its feasibility, safety, and validity in clinical practice.

Beyond Conventional Operations: Embracing the Era of Contemporary Minimally Invasive Cardiac Surgery

Over the past two decades, minimally invasive cardiac surgery (MICS) has gained a significant place due to the emergence of innovative tools and improvements in surgical techniques, offering comparable efficacy and safety to traditional surgical methods. This review provides an overview of the history of MICS, its current state, and its prospects and highlights its advantages and limitations. Additionally, we highlight the growing trends and potential pathways for the expansion of MICS, underscoring the crucial role of technological advancements in shaping the future of this field. Recognizing the challenges, we strive to pave the way for further breakthroughs in minimally invasive cardiac procedures.

A geometry-based finite element tool for evaluating mitral valve biomechanics

Mitral valve function depends on its complex geometry and tissue health, with alterations in shape and tissue response affecting the long-term restorarion of function. Previous computational frameworks for biomechanical assessment are mostly based on patient-specific geometries; however, these are not flexible enough to yield a variety of models and assess mitral closure for individually tuned morphological parameters or material property representations. This study details the finite element approach implemented in our previously developed toolbox to assess mitral valve biomechanics and showcases its flexibility through the generation and biomechanical evaluation of different models. A healthy valve geometry was generated and its computational predictions for biomechanics validated against data in the literature. Moreover, two mitral valve models including geometric alterations associated with disease were generated and analysed. The healthy mitral valve model yielded biomechanical predictions in terms of valve closure dynamics, leaflet stresses and papillary muscle and chordae forces comparable to previous computational and experimental studies. Mitral valve function was compromised in geometries representing disease, expressed by the presence of regurgitating areas, elevated stress on the leaflets and unbalanced subvalvular apparatus forces. This showcases the flexibility of the toolbox concerning the generation of a range of mitral valve models with varying geometric definitions and material properties and the evaluation of their biomechanics.

Computational Modeling of the Subject-Specific Effects of Annuloplasty Ring Sizing on the Mitral Valve to Repair Functional Mitral Regurgitation

Surgical repair of functional mitral regurgitation (FMR) that occurs in nearly 60% of heart failure (HF) patients is currently performed with undersizing mitral annuloplasty (UMA), which lacks short- and long-term durability. Heterogeneity in valve geometry makes tailoring this repair to each patient challenging, and predictive models that can help with planning this surgery are lacking. In this study, we present a 3D echo-derived computational model, to enable subject-specific, pre-surgical planning of the repair. Three computational models of the mitral valve were created from 3D echo data obtained in three pigs with HF and FMR. An annuloplasty ring model in seven sizes was created, each ring was deployed, and post-repair valve closure was simulated. The results indicate that large annuloplasty rings (> 32 mm) were not effective in eliminating regurgitant gaps nor in restoring leaflet coaptation or reducing leaflet stresses and chordal tension. Smaller rings (≤ 32 mm) restored better systolic valve closure in all investigated cases,but excessive valve tethering and restricted motion of the leaflets were still present. This computational study demonstrates that for effective correction of FMR, the extent of annular reduction differs between subjects, and overly reducing the annulus has deleterious effects on the valve.

Mechanical Behavior and Collagen Structure of Degenerative Mitral Valve Leaflets and a Finite Element Model of Primary Mitral Regurgitation

Degenerative mitral valve disease is the main cause of primary mitral regurgitation with two phenotypes: fibroelastic deficiency (FED) often with localized myxomatous degeneration and diffuse myxomatous degeneration or Barlow's disease. Myxomatous degeneration disrupts the microstructure of the mitral valve leaflets, particularly the collagen fibers, which affects the mechanical behavior of the leaflets. The present study uses biaxial mechanical tests and second harmonic generation microscopy to examine the mechanical behavior of Barlow and FED tissue. Three tissue samples were harvested from a FED patient and one sample is from a Barlow patient. Then we use an appropriate constitutive model by excluding the collagen fibers under compression. Finally, we built an FE model based on the echocardiography of patients diagnosed with FED and Barlow and the characterized material model and collagen fiber orientation. The Barlow sample and the FED sample from the most affected segment showed different mechanical behavior and collagen structure compared to the other two FED samples. The FE model showed very good agreement with echocardiography with 2.02±1.8 mm and 1.05±0.79 mm point-to-mesh distance errors for Barlow and FED patients, respectively. It has also been shown that the exclusion of collagen fibers under compression provides versatility for the material model; it behaves stiff in the belly region, preventing excessive bulging, while it behaves very softly in the commissures to facilitate folding. STATEMENT OF SIGNIFICANCE: None.

Long-term outcomes of etiology specific annuloplasty ring repair of ischemic mitral regurgitation

Background

Reductive annuloplasty repair of ischemic mitral regurgitation (IMR) is associated with high rates of recurrent MR, which may be improved with etiology-specific annuloplasty rings.

Methods

From October 2005 to May 2015, 128 consecutive patients underwent repair of IMR with the GeoForm ring. Clinical data was extracted from our local Society of Thoracic Surgeons database and electronic medical records. Mortality data was obtained from the Michigan State Social Security Death Index.

Results

The average age of patients was 65±11 years with mean pre-op left ventricular ejection fraction (LVEF) of 30%±10% and MR grade of 3.1±0.9 (0-4+). Thirty-day mortality was 4.7%, rate of renal failure 7.9%, rate of atrial fibrillation 27.3%, and no strokes were observed. Of the surviving patients, 89% (109/122) had a follow-up echocardiogram beyond 1 month with a mean echocardiographic follow-up of 59±39 months. LVEF improved from 30%±10% to 38%±14%, P<0.001) while end-diastolic (5.9±0.0 to 5.3±0.9 cm, P<0.001) and end-systolic (5.0±1.0 to 4.4±1.1 cm, P<0.001) left ventricular (LV) diameters decreased, as compared to pre-operative values. Seven patients were found to have recurrent moderate or greater IMR in follow-up to 10 years with three being due to ring dehiscence. One-, 5-, and 10-year freedom from recurrent moderate or severe IMR was 98%, 94%, and 80% respectively. One-, 5-, and 10-year survival was 91%, 77%, and 44%, respectively.

Conclusions

Overall, etiology-specific ring repair of IMR was associated with low rates of recurrent MR on long-term follow-up, coupled with significant LV reverse remodeling and improvement in ejection fraction.

Finite element analysis of annuloplasty and papillary muscle relocation on a patient-specific mitral regurgitation model

Objectives

Functional mitral regurgitation (FMR) is a significant complication of left ventricle (LV) dysfunction associated with poor prognosis and commonly treated by undersized ring annuloplasty. This study aimed to quantitatively simulate the treatment outcomes and mitral valve (MV) biomechanics following ring annulopalsty and papillary muscle relocation (PMR) procedures for a FMR patient.

Methods

We utilized a validated finite element model of the left heart for a patient with severe FMR and LV dilation from our previous study and simulated virtual ring annuloplasty procedures with various sizes of Edwards Classic and GeoForm annuloplasty rings. The model included detailed geometries of the left ventricle, mitral valve, and chordae tendineae, and incorporated age- and gender- matched nonlinear, anisotropic hyperelastic tissue material properties, and simulated chordal tethering at diastole due to LV dilation.

Results

Ring annuloplasty with either the Classic or GeoForm ring improved leaflet coaptation and increased the total leaflet closing force while increased posterior mitral leaflet (PML) stresses and strains. Classic rings resulted in larger coaptation forces and areas compared to GeoForm rings. The PMR procedure further improved the leaflet coaptation, decreased the PML stress and strain for both ring shapes and all sizes in this patient model.

Conclusions

This study demonstrated that a rigorously developed patient-specific computational model can provide useful insights into annuloplasty repair techniques for the treatment of FMR patients and could potentially serve as a tool to assist in pre-operative planning for MV repair surgical or interventional procedures.