Statistical assessment of normal mitral annular geometry using automated three-dimensional echocardiographic analysis

Euclidean and Shape-Based Analysis of the Dynamic Mitral Annulus in Children using a Novel Open-Source Framework

BACKGROUND

The dynamic shape of the normal adult mitral annulus has been shown to be important to mitral valve function. However, annular dynamics of the healthy mitral valve in children have yet to be explored. The aim of this study was to model and quantify the shape and major modes of variation of pediatric mitral valve annuli in four phases of the cardiac cycle using transthoracic echocardiography.

METHODS

The mitral valve annuli of 100 children and young adults with normal findings on three-dimensional echocardiography were modeled in four different cardiac phases using the SlicerHeart extension for 3D Slicer. Annular metrics were quantified using SlicerHeart, and optimal normalization to body surface area was explored. Mean annular shapes and the principal components of variation were computed using custom code implemented in a new SlicerHeart module (Annulus Shape Analyzer). Shape was regressed over metrics of age and body surface area, and mean shapes for five age-stratified groups were generated.

RESULTS

The ratio of annular height to commissural width of the mitral valve ("saddle shape") changed significantly throughout age for systolic phases (P < .001) but within a narrow range (median range, 0.20-0.25). Annular metrics changed statistically significantly between the diastolic and systolic phases of the cardiac cycle. Visually, the annular shape was maintained with respect to age and body surface area. Principal-component analysis revealed that the pediatric mitral annulus varies primarily in size (mode 1), ratio of annular height to commissural width (mode 2), and sphericity (mode 3).

CONCLUSIONS

The saddle-shaped mitral annulus is maintained throughout childhood but varies significantly throughout the cardiac cycle. The major modes of variation in the pediatric mitral annulus are due to size, ratio of annular height to commissural width, and sphericity. The generation of age- and size-specific mitral annular shapes may inform the development of appropriately scaled absorbable or expandable mitral annuloplasty rings for children.

SlicerHeart: An open-source computing platform for cardiac image analysis and modeling

Cardiovascular disease is a significant cause of morbidity and mortality in the developed world. 3D imaging of the heart's structure is critical to the understanding and treatment of cardiovascular disease. However, open-source tools for image analysis of cardiac images, particularly 3D echocardiographic (3DE) data, are limited. We describe the rationale, development, implementation, and application of SlicerHeart, a cardiac-focused toolkit for image analysis built upon 3D Slicer, an open-source image computing platform. We designed and implemented multiple Python scripted modules within 3D Slicer to import, register, and view 3DE data, including new code to volume render and crop 3DE. In addition, we developed dedicated workflows for the modeling and quantitative analysis of multi-modality image-derived heart models, including heart valves. Finally, we created and integrated new functionality to facilitate the planning of cardiac interventions and surgery. We demonstrate application of SlicerHeart to a diverse range of cardiovascular modeling and simulation including volume rendering of 3DE images, mitral valve modeling, transcatheter device modeling, and planning of complex surgical intervention such as cardiac baffle creation. SlicerHeart is an evolving open-source image processing platform based on 3D Slicer initiated to support the investigation and treatment of congenital heart disease. The technology in SlicerHeart provides a robust foundation for 3D image-based investigation in cardiovascular medicine.

DynaRing: A Patient-Specific Mitral Annuloplasty Ring With Selective Stiffness Segments

Annuloplasty ring choice and design are critical to the long-term efficacy of mitral valve (MV) repair. DynaRing is a selectively compliant annuloplasty ring composed of varying stiffness elastomer segments, a shape-set nitinol core, and a cross diameter filament. The ring provides sufficient stiffness to stabilize a diseased annulus while allowing physiological annular dynamics. Moreover, adjusting elastomer properties provides a mechanism for effectively tuning key MV metrics to specific patients. We evaluate the ring embedded in porcine valves with an ex-vivo left heart simulator and perform a 150 million cycle fatigue test via a custom oscillatory system. We present a patient-specific design approach for determining ring parameters using a finite element model optimization and patient MRI data. Ex-vivo experiment results demonstrate that motion of DynaRing closely matches literature values for healthy annuli. Findings from the patient-specific optimization establish DynaRing's ability to adjust the anterior-posterior and intercommissural diameters and saddle height by up to 8.8%, 5.6%, 19.8%, respectively, and match a wide range of patient data.

Dynamic Annular Modeling of the Unrepaired Complete Atrioventricular Canal Annulus

BACKGROUND

Repair of complete atrioventricular canal (CAVC) is often complicated by atrioventricular valve regurgitation, particularly of the left-sided valve. Understanding the 3-dimensional (3D) structure of the atrioventricular canal annulus before repair may help to inform optimized repair. However, the 3D shape and movement of the CAVC annulus has been neither quantified nor rigorously compared with a normal mitral valve annulus.

METHODS

The complete annuli of 43 patients with CAVC were modeled in 4 cardiac phases using transthoracic 3D echocardiograms and custom code. The annular structure was compared with the annuli of 20 normal pediatric mitral valves using 3D metrics and statistical shape analysis (Procrustes analysis).

RESULTS

The unrepaired CAVC annulus varied in shape significantly throughout the cardiac cycle. Procrustes analysis visually demonstrated that the average normalized CAVC annular shape is more planar than the normal mitral annulus. Quantitatively, the annular height-to-valve width ratio of the native left CAVC atrioventricular valve was significantly lower than that of a normal mitral valve in all systolic phases (P < .001).

CONCLUSIONS

The left half of the CAVC annulus is more planar than that of a normal mitral valve with an annular height-to-valve width ratio similar to dysfunctional mitral valves. Given the known importance of annular shape to mitral valve function, further exploration of the association of 3D structure to valve function in CAVC is warranted.

Dynamic changes of mitral valve annulus geometry at preprocedural CT: relationship with functional classes of regurgitation

BACKGROUND

We investigated mitral valve annular geometry changes during the cardiac cycle in patients with severe mitral regurgitation (MR) who underwent cardiac computed tomography angiography (CCTA) prior to percutaneous mitral valve replacement or annuloplasty.

METHODS

Fifty-one patients with severe MR and high surgical risk (Carpentier classification: 3 type I, 16 type II, 16 type IIIa, 16 type IIIb) underwent multiphase electrocardiographically gated (0-90%) CCTA, using a second generation dual-source CT scanner, as pre-procedural planning. Twenty-one patients without MR served as controls. The mitral valve annulus was segmented every 10% step of the R-R interval, according to the D-shaped segmentation model, and differences among groups were analysed by t-test or ANOVA.

RESULTS

Mitral annular area and diameters were larger in MR patients compared to controls, particularly in type II. Mitral annular area varied in MR patients throughout the cardiac cycle (mean ± standard deviation of maximum and minimum area 15.6 ± 3.9 cm² versus 13.0 ± 3.5 cm², respectively; p = 0.001), with greater difference between annular areas versus controls (2.59 ± 1.61 cm² and 1.98 ± 0.6 cm², p < 0.001). The largest dimension was found in systolic phases (20-40%) in most of MR patients (n = 27, 53%), independent of Carpentier type (I: n = 1, 33%; II: n = 10, 63%; IIIa: n = 8, 50%; IIIb: n = 8, 50%), and in protodiastolic phases (n = 14, 67%) for the control group.

CONCLUSIONS

In severe MR, mitral annular area varied significantly throughout the cardiac cycle, with a tendency towards larger dimensions in systole.

A toolbox for generating scalable mitral valve morphometric models

The mitral valve is a complex anatomical structure, whose shape is key to several traits of its function and disease, being crucial for the success of surgical repair and implantation of medical devices. The aim of this study was to develop a parametric, scalable, and clinically useful model of the mitral valve, enabling the biomechanical evaluation of mitral repair techniques through finite element simulations. MATLAB was used to parameterize the valve: the annular boundary was sampled from a porcine mitral valve mesh model and landmark points and relevant boundaries were selected for the parameterization of leaflets using polynomial fitting. Several geometric parameters describing the annulus, leaflet shape and papillary muscle position were implemented and used to scale the model according to patient dimensions. The developed model, available as a toolbox, allows for the generation of a population of models using patient-specific dimensions obtained from medical imaging or averaged dimensions evaluated from empirical equations based on the Golden Proportion. The average model developed using this framework accurately represents mitral valve shapes, associated with relative errors reaching less than 10% for annular and leaflet length dimensions, and less than 24% in comparison with clinical data. Moreover, model generation takes less than 5 min of computing time, and the toolbox can account for individual morphological variations and be employed to evaluate mitral valve biomechanics; following further development and validation, it will aid clinicians when choosing the best patient-specific clinical intervention and improve the design process of new medical devices.

Annular and subvalvular dynamics after extracellular matrix mitral tube graft implantation in pigs

OBJECTIVES

Entire mitral valve reconstruction with an extracellular matrix tube graft is a potential candidate to overcome the current limitations of mechanical and bioprosthetic valves. However, clinical data have raised concern with respect to patch failure. The aim of our study was to evaluate the impact of extracellular matrix mitral tube graft implantation on mitral annular and subvalvular regional dynamics in pigs.

METHODS

A modified tube graft design made of 2-ply extracellular matrix was used (CorMatrix®; Cardiovascular Inc., Alpharetta, GA, USA). The reconstructions were performed in an acute 80-kg porcine model (N = 8), where each pig acted as its own control. Haemodynamics were assessed with Mikro-Tip pressure catheters and mitral annular and subvalvular geometry and dynamics with sonomicrometry.

RESULTS

Catheter-based peak left atrial pressure and pressure difference across the mitral and aortic valves in the reconstructions were comparable to the values seen in the native mitral valves. Also comparable were maximum mitral annular area (755 ± 100 mm2), maximum septal-lateral distance (29.7 ± 1.7 mm), maximum commissure-commissure distance (35.0 ± 3.4 mm), end-systolic annular height-to-commissural width ratio (10.2 ± 1.0%) and end-diastolic interpapillary muscle distance (27.7 ± 3.3 mm). Systolic expansion of the mitral annulus was, however, observed after reconstruction.

CONCLUSIONS

The reconstructed mitral valves were fully functional without regurgitation, obstruction or stenosis. The reconstructed mitral annular and subvalvular geometry and subvalvular dynamics were found in the same range to those in the native mitral valve. A regional annular ballooning effect occurred that might predispose to patch failure. However, the greatest risk was found at the papillary muscle attachments.

Automating Model Generation for Image-Based Cardiac Flow Simulation

Computational fluid dynamics (CFD) modeling of left ventricle (LV) flow combined with patient medical imaging data has shown great potential in obtaining patient-specific hemodynamics information for functional assessment of the heart. A typical model construction pipeline usually starts with segmentation of the LV by manual delineation followed by mesh generation and registration techniques using separate software tools. However, such approaches usually require significant time and human efforts in the model generation process, limiting large-scale analysis. In this study, we propose an approach toward fully automating the model generation process for CFD simulation of LV flow to significantly reduce LV CFD model generation time. Our modeling framework leverages a novel combination of techniques including deep-learning based segmentation, geometry processing, and image registration to reliably reconstruct CFD-suitable LV models with little-to-no user intervention.1 We utilized an ensemble of two-dimensional (2D) convolutional neural networks (CNNs) for automatic segmentation of cardiac structures from three-dimensional (3D) patient images and our segmentation approach outperformed recent state-of-the-art segmentation techniques when evaluated on benchmark data containing both magnetic resonance (MR) and computed tomography(CT) cardiac scans. We demonstrate that through a combination of segmentation and geometry processing, we were able to robustly create CFD-suitable LV meshes from segmentations for 78 out of 80 test cases. Although the focus on this study is on image-to-mesh generation, we demonstrate the feasibility of this framework in supporting LV hemodynamics modeling by performing CFD simulations from two representative time-resolved patient-specific image datasets.

Geometric description for the anatomy of the mitral valve: A review

The mitral valve is a complex anatomical structure whose physiological functioning relies on the biomechanical properties and structural integrity of its components. Their compromise can lead to mitral valve dysfunction, associated with morbidity and mortality. Therefore, a review on the morphometry of the mitral valve is crucial, more specifically on the importance of valve dimensions and shape for its function. This review initially provides a brief background on the anatomy and physiology of the mitral valve, followed by an analysis of the morphological information available. A characterisation of mathematical descriptions of several parts of the valve is performed and the impact of different dimensions and shape changes in disease is then outlined. Finally, a section regarding future directions and recommendations for the use of morphometric information in clinical analysis of the mitral valve is presented.

Cardiac Magnetic Resonance Analysis of Mitral Annular Dynamics after Mitral Valve Repair

OBJECTIVES

The aim of this study was to analyze mitral annulus (MA) dynamics using cardiac magnetic resonance (CMR) in patients with degenerative mitral insufficiency who underwent mitral valve repair (MVR).

METHODS

Mitral valve imaging was performed by CMR in twenty-nine patients with degenerative mitral insufficiency who underwent MVR between July 2014 and August 2016, with quadrangular resection of the posterior leaflet without ring annuloplasty. They were prospectively followed up from the preoperative period up to 2 years postoperatively.

RESULTS

We observed a significant reduction in all measurements of the MA after surgery. The mean systolic circumference of the MA was reduced from 13.28±1.95 cm to 11.50±1.59 cm, and the diastolic circumference was reduced from 12.51±2.01 cm to 10.66±2.09 cm in the immediate postoperative period, measures that remained stable 2 years after MVR (p<0.001). The mean maximum area of the MA was significantly reduced from 14.34±4.03 to 10.45±3.17 cm2 when comparing the immediate postoperative period and the 2 year follow-up (p<0.001). The same occurred with the mean minimum area of the MA, which was reduced from 12.53±3.68 cm2 to 9.23±2.84 cm2 in the same period, and this reduction was greater in the antero-posterior diameter than in the mid-lateral diameter. The mobility of the MA was preserved after surgery, ranging between 19.6% and 25.7% at 2-year follow-up.

CONCLUSION

We observed a significant reduction in the MA size after MVR, with preservation of the MA mobility at the 2-year follow-up.

Semi-automated Image Segmentation of the Midsystolic Left Ventricular Mitral Valve Complex in Ischemic Mitral Regurgitation

Ischemic mitral regurgitation (IMR) is primarily a left ventricular disease in which the mitral valve is dysfunctional due to ventricular remodeling after myocardial infarction. Current automated methods have focused on analyzing the mitral valve and left ventricle independently. While these methods have allowed for valuable insights into mechanisms of IMR, they do not fully integrate pathological features of the left ventricle and mitral valve. Thus, there is an unmet need to develop an automated segmentation algorithm for the left ventricular mitral valve complex, in order to allow for a more comprehensive study of this disease. The objective of this study is to generate and evaluate segmentations of the left ventricular mitral valve complex in pre-operative 3D transesophageal echocardiography using multi-atlas label fusion. These patient-specific segmentations could enable future statistical shape analysis for clinical outcome prediction and surgical risk stratification. In this study, we demonstrate a preliminary segmentation pipeline that achieves an average Dice coefficient of 0.78 ± 0.06.

Dynamic Three-Dimensional Geometry of the Tricuspid Valve Annulus in Hypoplastic Left Heart Syndrome with a Fontan Circulation

BACKGROUND

Tricuspid regurgitation (TR) is a significant contributor to morbidity and mortality in patients with hypoplastic left heart syndrome. The goal of this study was to characterize the dynamic annular motion of the tricuspid valve in patients with HLHS with a Fontan circulation and assess the relation to tricuspid valve function.

METHODS

Tricuspid annuli of 48 patients with HLHS with a Fontan circulation were modeled at end-diastole, mid-systole, end-systole, and mid-diastole using transthoracic three-dimensional echocardiography and custom code in 3D Slicer. The angle of the anterior papillary muscle (APM) relative to the annular plane in each systolic phase was also measured.

RESULTS

Imaging was performed 5.0 years (interquartile range, 2-11 years) after Fontan operation. The tricuspid annulus varies in shape significantly throughout the cardiac cycle, changing in sphericity (P < .001) but not in annular height or bending angle. In univariate modeling, patients with significant TR had larger changes in septolateral diameter, lateral quadrant area, and posterior quadrant area (P < .05 for all) as well as lower (more laterally directed) APM angles (P < .001) than patients with mild or less TR. In multivariate modeling, a 1 mm/(body surface area)^0.5 increase in the maximum change in septolateral diameter was associated with a 1.7-fold increase in having moderate or greater TR, while a 10° decrease in APM angle at mid-systole was associated with an almost 2.5-fold increase in moderate or greater TR (P ≤ .01 for all).

CONCLUSIONS

The tricuspid annulus in patients with HLHS with a Fontan circulation changes in shape significantly throughout the cardiac cycle but remains relatively planar. Increased change in septolateral diameter and decreased APM angle are strongly associated with the presence of TR. These findings may inform annuloplasty methods and subvalvular interventions in these complex patients.

Three-Dimensional Mitral Valve Morphology in Children and Young Adults With Marfan Syndrome

BACKGROUND

Mitral valve (MV) prolapse is common in children with Marfan syndrome (MFS) and is associated with varying degrees of mitral regurgitation (MR). However, the three-dimensional (3D) morphology of the MV in children with MFS and its relation to the degree of MR are not known. The goals of this study were to describe the 3D morphology of the MV in children with MFS and to compare it to that in normal children.

METHODS

Three-dimensional transthoracic echocardiography was performed in 27 patients (3-21 years of age) meeting the revised Ghent criteria for MFS and 27 normal children matched by age (±1 year). The 3D geometry of the MV apparatus in midsystole was measured, and its association with clinical and two-dimensional echocardiographic parameters was examined.

RESULTS

Compared with age-matched control subjects, children with MFS had larger 3D annular areas (P < .02), smaller annular height/commissural width ratios (P < .001), greater billow volumes (P < .001), and smaller tenting heights, areas, and volumes (P < .001 for all). In multivariate modeling, larger leaflet billow volume in MFS was strongly associated with moderate or greater MR (P < .01). Intra- and interuser variability of 3D metrics was acceptable.

CONCLUSIONS

Children with MFS have flatter and more dilated MV annuli, greater billow volumes, and smaller tenting heights compared with normal control subjects. Larger billow volume is associated with MR. Three-dimensional MV quantification may contribute to the identification of patients with MFS and other connective tissue disorders. Further study of 3D MV geometry and its relation to the clinical progression of MV disease is warranted in this vulnerable population.

Three-Dimensional Mitral Valve Morphology and Age-Related Trends in Children and Young Adults with Structurally Normal Hearts Using Transthoracic Echocardiography

BACKGROUND

The mitral valve has a complex three-dimensional (3D) morphology that is incompletely described by two-dimensional echocardiography (echo). Three-dimensional echo provides a more robust tool to analyze the mitral valve. The shape of the mitral annulus and leaflets, and differences with age, have not been described by 3D echo in normal children. Our objective was to characterize and quantify the 3D mitral valve morphology in children with normal transthoracic echocardiograms over a broad spectrum of age and to identify differences in valve shape with age.

METHODS

Three-dimensional midsystolic mitral valve models were constructed in 100 children and young adults with normal echocardiograms using 3D transthoracic images. Annular and leaflet metrics were quantified and regression equations were prepared. Interuser and intrauser variability was measured.

RESULTS

Two hundred fifty patients, from neonate to young adult, were retrospectively reviewed to obtain 100 evaluable patients (40% evaluable). The annular height to commissural width ratio of the mitral valve ("saddle shape") was preserved across age (median 24.3, IQR 21.8-28.1). Three-dimensional mitral valve area, length, and volume parameters were linearly related to body surface area (P < .001). The ratio of anterior to posterior leaflet length and posterior leaflet angle increased with body surface area (P = .0004 and .002, respectively) suggesting posterior movement of the coaptation line. Two-dimensional lateral annular diameter underestimated 3D lateral annular metrics (P < .001, mean difference 20-22%) but was highly correlated (R > 0.87, P < .001). Interuser and intrauser variability were acceptable.

CONCLUSIONS

Assessment of 3D mitral valve morphology in children is possible in a modern clinical pediatric echocardiography laboratory using transthoracic images, although further optimization of imaging is needed. The saddle shape of the mitral annulus was preserved across age and size. Most mitral valve parameters increased linearly with patient size. Further investigation is warranted to explore changes in valve morphology in the pediatric population in health and with disease.

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.