Utilization of Engineering Advances for Detailed Biomechanical Characterization of the Mitral-Ventricular Relationship to Optimize Repair Strategies: A Comprehensive Review

The geometrical details and biomechanical relationships of the mitral valve-left ventricular apparatus are very complex and have posed as an area of research interest for decades. These characteristics play a major role in identifying and perfecting the optimal approaches to treat diseases of this system when the restoration of biomechanical and mechano-biological conditions becomes the main target. Over the years, engineering approaches have helped to revolutionize the field in this regard. Furthermore, advanced modelling modalities have contributed greatly to the development of novel devices and less invasive strategies. This article provides an overview and narrative of the evolution of mitral valve therapy with special focus on two diseases frequently encountered by cardiac surgeons and interventional cardiologists: ischemic and degenerative mitral regurgitation.

3D echocardiography in mitral valve prolapse

Mitral valve prolapse (MVP) is the leading cause of mitral valve surgery. Echocardiography is the principal imaging modality used to diagnose MVP, assess the mitral valve morphology and mitral annulus dynamics, and quantify mitral regurgitation. Three-dimensional (3D) echocardiographic (3DE) imaging represents a consistent innovation in cardiovascular ultrasound in the last decades, and it has been implemented in routine clinical practice for the evaluation of mitral valve diseases. The focus of this review is the role and the advantages of 3DE in the comprehensive evaluation of MVP, intraoperative and intraprocedural monitoring.

Three-Dimensional Transthoracic Static and Dynamic Normative Values of the Mitral Valve Apparatus: Results from the Multicenter World Alliance Societies of Echocardiography Study

BACKGROUND

Recent advances in mitral valve (MV) percutaneous interventions have escalated the need for a more quantitative and comprehensive assessment of the MV, which can be best achieved using three-dimensional echocardiography. Understanding normal valve size, structure, and function is essential for differentiation of healthy from disease states. The aims of this study were to establish normative values for MV apparatus size and morphology and to determine how they vary across age, sex, and race groups using data from the World Alliance Societies of Echocardiography Normal Values Study.

METHODS

Three-dimensional volumetric data sets obtained on transthoracic echocardiography in 748 normal subjects (51% men) were analyzed using commercial MV analysis software (TomTec Imaging Systems) to determine annular and leaflet dimensions and areas. The subjects were divided into groups by sex (378 men and 370 women) and age (18 to 40 years [n = 266], 41 to 65 years [n = 249], and >65 years [n = 233]) to identify sex- and age-related differences. In addition, differences among black, white, and Asian populations were studied. Inter- and intraobserver variability was assessed in a subset of 30 subjects and expressed as mean absolute difference between pairs of repeated measurements.

RESULTS

Compared with women, men had larger annular size measurements, larger tenting size parameters, and larger leaflet length and area. Compared with the black and white populations, the Asian population showed significantly smaller mitral annular size. Although many of the age, sex, and race differences in MV parameters were statistically significant, they were comparable with or smaller than the corresponding measurement variability. Indexing to body surface area and height did not eliminate these differences consistently, suggesting that parameters may need to be indexed according to their dimensionality.

CONCLUSIONS

This analysis of the World Alliance Societies of Echocardiography data provides normative values of mitral apparatus size and morphology. Although sex- and age-related differences were noted, they need to be interpreted with caution in view of the associated measurement variability.

Mitral Annular Forces and Their Potential Impact on Annuloplasty Ring Selection

Objectives: To provide an overview that describes the characteristics of a mitral annuloplasty device when treating patients with a specific type of mitral regurgitation according to Carpentier's classification of mitral regurgitation.

Methods: Starting with the key search term “mitral valve annuloplasty,” a literature search was performed utilising PubMed, Google Scholar, and Web of Science to identify relevant studies. A systematic approach was used to assess all publications.

Results: Mitral annuloplasty rings are traditionally categorised by their mechanical compliance in rigid-, semi-rigid-, and flexible rings. There is a direct correlation between remodelling capabilities and rigidity. Thus, a rigid annuloplasty ring will have the highest remodelling capability, while a flexible ring will have the lowest. Rigid- and semi-rigid rings can furthermore be divided into flat and saddled-shaped rings. Saddle-shaped rings are generally preferred over flat rings since they decrease annular and leaflet stress accumulation and provide superior leaflet coaptation. Finally, mitral annuloplasty rings can either be complete or partial.

Conclusions: A downsized rigid- or semi-rigid ring is advantageous when higher remodelling capabilities are required to correct dilation of the mitral annulus, as seen in type I, type IIIa, and type IIIb mitral regurgitation. In type II mitral regurgitation, a normosized flexible ring might be sufficient and allow for a more physiological repair since there is no annular dilatation, which diminishes the need for remodelling capabilities. However, mitral annuloplasty ring selection should always be based on the specific morphology in each patient.

Novelties in 3D Transthoracic Echocardiography

Cardiovascular imaging is developing at a rapid pace and the newer modalities, in particular three-dimensional echocardiography, allow better analysis of heart structures. Identifying valve lesions and grading their severity represents crucial information and nowadays is strengthened by the introduction of new software, such as transillumination, which provide detailed morphology descriptions. Chambers quantification has never been so rapid and accurate: machine learning algorithms generate automated volume measurements, including left ventricular systolic and diastolic function, which is extremely important for clinical decisions. This review provides an overview of the latest innovations in the echocardiography field, and is helpful by providing a better insight into heart diseases.

Effects of nonvalvular atrial fibrillation on the structure and function of mitral valves (a STROBE-compliant article)

The aim of this study was to explore the effects of nonvalvular atrial fibrillation (NVAF) on the structure and function of mitral valve and analyze independent risk factors of moderate to severe mitral regurgitation (MR) by quantitative measurement of mitral parameters using real-time 3-dimensional transesophageal echocardiography.This study included 30 subjects with sinus rhythm group, and 65 patients with NVAF. The 65 patients with NVAF were divided into 35 with paroxysmal atrial fibrillation group and 30 with persistent atrial fibrillation. According to MR degree, the patients with NVAF were again divided into no or mild MR group (n = 44) and moderate to severe MR group (n = 21).There were significant differences in anterolateral-to-posteromedial diameter (DAlPm), anterior-to-posterior diameter, 3-dimensional circumference (C3D), 2-dimensional area (A2D), mitral leaflet surface area in late systolic phase, the index of mitral valve coaptation and left atrial internal diameter (LAID) between different cardiac rhythm groups (all P < .05). The DAlPm, C3D, A2D, nonplanar angle (θNPA), and LAID were greater but the mitral valve coaptation index was smaller in the moderate to severe MR group than in the no or mild MR group (all P < .05). Logistic regression analysis indicated that DAlPm and LAID were independent risk factors of moderate to severe MR in the patients with NVAF (OR > 1, P < .05).DAlPm and LAID are independent risk factors of moderate to severe MR in the patients with NVAF. NVAF can change the structure and function of mitral valve, which leads to MR.

Impact of different annuloplasty rings on geometry of the mitral annulus with fibroelastic deficiency: the significance of aorto-mitral angle

We sought to investigate the impact of full annuloplasty rings versus C-shape bands on mitral annular geometry in the presence of fibroelastic deficiency (FED), as assessed by intraoperative three-dimensional transesophageal echocardiography (3DTEE). We retrospectively selected 65 patients who underwent mitral valve repair for severe mitral regurgitation caused by FED using full rings (the Ring group, n = 30) and C-shape bands (the Band group, n = 35). 71 controls without valvular heart disease were also included. Thorough 3DTEE inspections were performed for the entire cohort to measure morphological parameters of mitral annulus before and after surgery. Mid-term repair durability and left atrial diameter were followed up. The preoperative 3DTEE parameters, including annular diameters, area, height and aorto-mitral angle, were significantly larger in the FED groups than normal, and were comparable between two groups using different annuloplasty devices. After repair, the anterior-posterior diameter, annulus circumference and area were significantly larger in the Band group than in the Ring group. The aorto-mitral angle became comparable with normal value in the Ring group (p = 0.728), but not in the Band group (p = 0.011). Follow-up echocardiographic data showed a significant correlation between postoperative aorto-mitral angle and reduced left atrial diameter at 50.3 months after surgery (r = 0.63; p < 0.001). In conclusion, compared with C-shape bands, full rings may impose less narrowing on aorto-mitral angle, which correlates well with mid-term left atrial reverse remodeling.

Dynamic and quantitative evaluation of degenerative mitral valve disease: a dedicated framework based on cardiac magnetic resonance imaging

BACKGROUND

Accurate quantification of mitral valve (MV) morphology and dynamic behavior over the cardiac cycle is crucial to understand the mechanisms of degenerative MV dysfunction and to guide the surgical intervention. Cardiac magnetic resonance (CMR) imaging has progressively been adopted to evaluate MV pathophysiology, although a dedicated framework is required to perform a quantitative assessment of the functional MV anatomy.

METHODS

We investigated MV dynamic behavior in subjects with normal MV anatomy (n=10) and patients referred to surgery due to degenerative MV prolapse, classified as fibro-elastic deficiency (FED, n=9) and Barlow's disease (BD, n=10). A CMR-dedicated framework was adopted to evaluate prolapse height and volume and quantitatively assess valvular morphology and papillary muscles (PAPs) function over the cardiac cycle. Multiple comparison was used to investigate the hallmarks associated to MV degenerative prolapse and evaluate the feasibility of anatomical and functional distinction between FED and BD phenotypes.

RESULTS

On average, annular dimensions were significantly (P<0.05) larger in BD than in FED and normal subjects while no significant differences were noticed between FED and normal. MV eccentricity progressively decreased passing from normal to FED and BD, with the latter exhibiting a rounder annulus shape. Over the cardiac cycle, we noticed significant differences for BD during systole with an abnormal annular enlargement between mid and late systole (LS) (P<0.001 vs. normal); the PAPs dynamics remained comparable in the three groups. Prolapse height and volume highlighted significant differences among normal, FED and BD valves.

CONCLUSIONS

Our CMR-dedicated framework allows for the quantitative and dynamic evaluation of MV apparatus, with quantifiable annular alterations representing the primary hallmark of severe MV degeneration. This may aid surgeons in the evaluation of the severity of MV dysfunction and the selection of the appropriate MV treatment.

Mitral Valve Chordae Tendineae: Topological and Geometrical Characterization

Mitral valve (MV) closure depends upon the proper function of each component of the valve apparatus, which includes the annulus, leaflets, and chordae tendineae (CT). Geometry plays a major role in MV mechanics and thus highly impacts the accuracy of computational models simulating MV function and repair. While the physiological geometry of the leaflets and annulus have been previously investigated, little effort has been made to quantitatively and objectively describe CT geometry. The CT constitute a fibrous tendon-like structure projecting from the papillary muscles (PMs) to the leaflets, thereby evenly distributing the loads placed on the MV during closure. Because CT play a major role in determining the shape and stress state of the MV as a whole, their geometry must be well characterized. In the present work, a novel and comprehensive investigation of MV CT geometry was performed to more fully quantify CT anatomy. In vitro micro-tomography 3D images of ovine MVs were acquired, segmented, then analyzed using a curve-skeleton transform. The resulting data was used to construct B-spline geometric representations of the CT structures, enriched with a continuous field of cross-sectional area (CSA) data. Next, Reeb graph models were developed to analyze overall topological patterns, along with dimensional attributes such as segment lengths, 3D orientations, and CSA. Reeb graph results revealed that the topology of ovine MV CT followed a full binary tree structure. Moreover, individual chords are mostly planar geometries that together form a 3D load-bearing support for the MV leaflets. We further demonstrated that, unlike flow-based branching patterns, while individual CT branches became thinner as they propagated further away from the PM heads towards the leaflets, the total CSA almost doubled. Overall, our findings indicate a certain level of regularity in structure, and suggest that population-based MV CT geometric models can be generated to improve current MV repair procedures.

Three-dimensional dynamic morphology of the mitral valve in different forms of mitral valve prolapse - potential implications for annuloplasty ring selection

Background

Real-time three-dimensional transesophageal echocardiography has increased our understanding of the distinct pathomechanisms underlying functional, ischaemic or degenerative mitral regurgitation. However, potential differences in dynamic morphology between the subtypes of degenerative mitral prolapse have scarcely been investigated.

Methods

In order to compare the dynamic behavior of the different phenotypes of degenerative mitral valve prolapse, real-time three-dimensional transesophageal echocardiography recordings of 77 subjects, 27 with Barlow disease (BD), 32 with Fibroelastic deficiency (FED) and 18 normal controls (NC) were analysed.

Results

Geometric annular and valvular parameters of the myxomatous patients were significantly larger compared to controls (BD vs. FED vs. NC 3D annular area: 15 ± 2.8 vs. 13.3 ± 2.4 vs. 10.6 ± 2.3cm², all p < 0.01). Beside similar ellipticity, BD annuli were significantly flatter compared to FED. Myxomatous annuli appeared less dynamic than normals, with decreased overall 3D area change, however only the BD group differed from NC significantly (BD vs. FED vs. NC normalized 3D area change 4.40 vs. 6.81 vs. 9.69 %; BD vs. NC p = 0.000; FED vs. NC p = not significant, BD vs. FED p = 0.025).

Conclusion

BD and FED differ not only in terms of valve morphology, but also annular dynamics. Both pathologies are characterized by annular dilatation. However, in BD the annulus is remarkably flattened and hypodynamic, whereas in FED its saddle-shape and contractile function is relatively preserved. These features might influence the choice of repair technique and the selection of annuloplasty ring.

Non-ischaemic mitral valve suture annuloplasty: late follow-up results

Objective:

To evaluate late outcomes after posterior mitral valve (MV) annulus double-suture annuloplasty for degenerative (non-ischaemic) MV insufficiency.

Design:

Between 2005 and 2011, 138 patients underwent MV repair using posterior MV double-suture annuloplasty and an additional 105 patients underwent tricuspid valve repair. The study protocol included operative mortality, reoperation rate and reasons, as well as echocardiographic parameters at pre- and postoperative and follow-up periods (2-9 years).

Results:

In-hospital mortality was 2/138 (1.45%). Early post operation, no regurgitation was noted in 74/136 (54.4%) patients, Io regurgitation was observed in 55/136 (40.4%), IIo was observed in 6/136 (4.4%) and IIIo was observed in 1/136 (0.7%); during late follow-up (from 2 to 9 years), no regurgitation was observed in 21.6% patients, Io was observed in 58%, IIo was observed in 17% and IIIo was observed in 3.4%. The mean preoperative anterolateral diameter of the MV annulus was 39.02±4.97 mm and, at late follow-up, it was 27.66±3.94 mm (p=0.000); at these same time points, left ventricular end-diastolic diameter (LVEDD) was 55.74±7.29 mm and 49.17±6.01 mm (p=0.000), respectively, and the left ventricular ejection fraction (LVEF) was 53.08±8.93% and 50.92±6.78%, respectively (p=0.007).

Conclusions:

This study demonstrates suture annuloplasty to be an effective treatment up to 9 years for degenerative mitral valve disease. This technique enables preservation of the posterior mitral valve annulus diameter with stable long-term (up to 9 years) reduction, a competent (no regurgitation/⩽IIo regurgitation) MV in 96.6% of cases and positive left ventricular (LV) remodelling.

Semi-automated segmentation and quantification of mitral annulus and leaflets from transesophageal 3-D echocardiographic images

Quantification of three-dimensional (3-D) morphology of the mitral valve (MV) using real-time 3-D transesophageal echocardiography (RT3-D TEE) has proved to be a valuable tool for the assessment of MV pathologies, but of limited use in clinical practice because it relies on user-intensive approaches. This study presents a new algorithm for the segmentation and morphologic quantification of the mitral annulus (MA) and mitral leaflets (ML) in closed valve configuration from RT3-D TEE volumes. Following initialization, the MA and the ML and the coaptation line (CL) are automatically obtained in 3-D. Validation with manual tracings was performed on 33 patients, resulting in segmentation errors in the order of 0.7 mm and 0.6 mm for the MA and ML segmentation, in addition to good intra- and inter-observer reproducibility (coefficients of variation below 12% and 15%, respectively). The ability of the algorithm to assess different MV pathologies as well as repaired valves with implanted annular rings was also explored. The reported performance of the proposed fast, semi-automated MA and ML quantification makes it promising for future applications in clinical settings such as the operating room, where obtaining results in short time is important.

Three-Dimensional Echocardiography: Advancements in Qualitative and Quantitative Analyses of Mitral Valve Morphology in Mitral Valve Prolapse

Degenerative mitral valve disease (MVD) is the leading cause of organic mitral regurgitation (MR), one of the most common valvular heart disease in western countries. Substantial progresses in the surgical treatment of degenerative MVD have improved life expectancy of patients with significant MR. However, prognosis, surgical decision and timing of surgery strongly depend on the accurate characterization of mitral valve (MV) anatomy and pathology and on the precise quantification of MR. Three-dimensional (3D) echocardiography, a major technological breakthrough in the field of cardiovascular imaging, provides several advantages over two-dimensional (2D) imaging in the qualitative and quantitative evaluations of MV apparatus. In this review, we focus on the contribution of this new modality to the diagnosis of degenerative MVD, the quantitative assessment of MR severity, the selection and monitoring of surgical and percutaneous procedures, the evaluation of procedural outcomes. The results of a systematic and exhaustive search of the existing literature, restricted to real-time 3D echocardiography in adults, are here reported.

Three-dimensional echocardiography of the mitral valve: lessons learned

Three-dimensional echocardiography has markedly improved our understanding of normal and pathologic mitral valve (MV) mechanics. Qualitative and quantitative analysis of three-dimensional (3D) data on the mitral valve could have a clinical impact on diagnosis, patient referral, surgical strategies, annuloplasty ring design and evaluation of the immediate and long-term surgical outcome. This review covers the contribution of 3D echocardiography in the diagnosis of MV disease, its role in selecting and monitoring surgical procedures, and in the assessment of surgical outcomes. Moreover, advantages of this technique versus the standard 2D modality, as well as future applications of advanced analysis techniques, will be reviewed.

Dynamic indices of mitral valve function using perioperative three-dimensional transesophageal echocardiography

OBJECTIVE

Perioperative transesophageal echocardiography is essential for decision-making for mitral valve surgery. While two-dimensional transesophageal echocardiography represents the standard of care, tracking of dynamic changes using three-dimensional imaging permits assessment of morphologic and functional characteristics of the mitral valve. The authors hypothesized that quantitative three-dimensional analysis would reveal distinct differences among diseased, repaired, and normal mitral valves.

DESIGN

Case-control observational clinical study.

SETTING

Tertiary care hospital.

PARTICIPANTS

Using novel mitral valve quantification software, the authors retrospectively analyzed 80 datasets of cardiac surgery patients who underwent intraoperative transesophageal echocardiographic imaging. Twenty patients with degenerative mitral regurgitation were evaluated before and after mitral valve repair. Twenty patients had functional mitral regurgitation, and 20 patients had no mitral valve disease.

MEASUREMENTS AND MAIN RESULTS

Primary outcome measures of dynamic mitral valve function were: 1) three-dimensional annulus area, 2) annular displacement distance, 3) annular displacement velocity, and 4) annular area fraction. Other mitral annular tracking indices, in addition to intraobserver reliability and interobserver agreement, also were reported. Annulus area was enlarged in degenerative and functional mitral regurgitation. Annular displacement distance was decreased in functional mitral regurgitation and repaired valves. Annular displacement velocity was decreased in functional mitral regurgitation. Annular area fraction was decreased in functional mitral regurgitation and repaired valves. Intraobserver reliability and interobserver agreement were high for all 4 analyzed indices.

CONCLUSIONS

Normal, functional regurgitant, degenerative, and repaired mitral valves have distinctly different dynamic signatures of anatomy and function as reliably determined by perioperative echocardiographic tracking.

The once and future state of percutaneous mitral valve repair

There has been a great deal of interest in percutaneous mitral valve repair techniques in recent years, with several devices undergoing animal testing and clinical trials. Percutaneous annuloplasty and leaflet repair devices are currently in development, and while safety rates have generally been equal or superior to conventional surgical techniques, efficacy has been suboptimal. Most current percutaneous mitral valve repair devices can only reduce regurgitant volumes by approximately 20-40%, but these reductions may be enough to treat high-risk patients, including the elderly and those with comorbidities, who are otherwise ineligible for surgery. An analysis of how these devices alter the geometry and mechanics of the mitral valve apparatus can provide insight into long-term efficacy and durability and may lead to improvements in the reduction of mitral regurgitation. In the future, multiple percutaneous techniques may be utilized in combination to increase overall efficacy. In this article, we report on percutaneous mitral valve repair techniques with published clinical or animal data.

Mechanism of valvular regurgitation

PURPOSE OF REVIEW

Despite improvements in surgical techniques, valvular regurgitation results in major morbidity in children with heart disease. Functional anatomy, mechanisms of valve closure and adaptation to changing hemodynamic stress in normal mitral and tricuspid valves are complex and only partially understood. As well, pathology of atrioventricular valve regurgitation is further complicated by congenital valve abnormalities involving leaflet tissue, supporting chordal apparatus and displaced papillary muscles. This review provides a current understanding of the mechanisms that result in atrioventricular valve failure.

RECENT FINDINGS

Mitral valve leaflets have contractile elements, in addition to atrial muscle modulation of leaflet tension. When placed under mechanical tethering stress, the mitral valve adapts by leaflet expansion, which increases coaptation surface reserve and chordal thickening. Both pediatric and adult studies are increasingly reporting on the importance of subvalvar apparatus function in maintaining valve competency.

SUMMARY

The maintenance of efficient valve function is accomplished by a complex series of events involving atrial and annular contraction, annular deformation, active leaflet tension, chordal transmission of papillary muscle contractions and ventricular contraction.