Bayesian Optimization-Based Inverse Finite Element Analysis for Atrioventricular Heart Valves.

Inverse finite element analysis (iFEA) of the atrioventricular heart valves (AHVs) can provide insights into the in-vivo valvular function, such as in-vivo tissue strains; however, there are several limitations in the current state-of-the-art that iFEA has not been widely employed to predict the in-vivo, patient-specific AHV leaflet mechanical responses. In this exploratory study, we propose the use of Bayesian optimization (BO) to study the AHV functional behaviors in-vivo. We analyzed the efficacy of Bayesian optimization to estimate the isotropic Lee-Sacks material coefficients in three benchmark problems: (i) an inflation test, (ii) a simplified leaflet contact model, and (iii) an idealized AHV model. Then, we applied the developed BO-iFEA framework to predict the leaflet properties for a patient-specific tricuspid valve under a congenital heart defect condition. We found that the BO could accurately construct the objective function surface compared to the one from a [Formula: see text] grid search analysis. Additionally, in all cases the proposed BO-iFEA framework yielded material parameter predictions with average element errors less than 0.02 mm/mm (normalized by the simulation-specific characteristic length). Nonetheless, the solutions were not unique due to the presence of a long-valley minima region in the objective function surfaces. Parameter sets along this valley can yield functionally equivalent outcomes (i.e., closing behavior) and are typically observed in the inverse analysis or parameter estimation for the nonlinear mechanical responses of the AHV. In this study, our key contributions include: (i) a first-of-its-kind demonstration of the BO method used for the AHV iFEA; and (ii) the evaluation of a candidate AHV in-silico modeling approach wherein the chordae could be substituted with equivalent displacement boundary conditions, rendering the better iFEA convergence and a smoother objective surface.

Papillary muscle approximation in chronic ovine functional tricuspid regurgitation.

OBJECTIVE: Isolated tricuspid ring annuloplasty remains the surgical standard for functional tricuspid regurgitation repair but offers suboptimal results when right ventricular dilation and remodeling along with papillary muscle displacement is present. Addressing subvalvular remodeling with papillary muscle approximation may improve clinical outcomes. METHODS: Functional tricuspid regurgitation and biventricular dysfunction were induced in 8 healthy sheep by rapid ventricular pacing (200-240 bpm) for 27 ± 6 days. Subsequently, animals underwent cardiopulmonary bypass for implantation of sonomicrometry crystals on the tricuspid annulus, right ventricle, and papillary muscle tips. Papillary approximation sutures were anchored between anterior-posterior and anterior-septal papillary muscles and externalized through right ventricular free wall to epicardial tourniquets. After weaning from cardiopulmonary bypass, sequential papillary muscle approximations were performed. Simultaneous hemodynamic, sonomicrometry, and echocardiographic data were collected at baseline and after each papillary muscle approximation. RESULTS: With rapid pacing, right ventricular fractional area change decreased from 59 ± 6% to 38 ± 8% (P < .001), whereas tricuspid annulus diameter increased from 2.4 ± 0.3 cm to 3.3 ± 0.6 cm (P = .003). Tricuspid regurgitation (0-4+) increased from +0 ± 0 to +3.3 ± 0.7 (P < .001). Both anterior-posterior and anterior-septal papillary muscle approximation significantly reduced functional tricuspid regurgitation from +3.3 ± 0.7 to +2 ± 0.5 and +1.9 ± 0.6, respectively (P < .001). Reduction of tricuspid insufficiency with both subvalvular interventions was associated with decreased distance of the anterior papillary muscle to the annular centroid. CONCLUSIONS: Papillary muscle approximations were effective in reducing severe ovine functional tricuspid regurgitation associated with right ventricular dilation and papillary muscle displacement. Further studies are needed to evaluate efficacy of this adjunct to ring annuloplasty in repair of severe functional tricuspid regurgitation.

An unusual origin of a papillary muscle of the right ventricle.

Knowledge of anatomical variations of the heart are important to cardiac surgeons, cardiologists, and radiologist. During routine dissection of a 77-year-old male cadaver, we observed an unusual origin of a papillary muscle of the right ventricle arising from the atrioventricular aspect of the moderator band. This papillary muscle was 6.7mm long and 2.6mm wide. It gave rise to two chordae tendineae: one to the inferior (posterior) papillary muscle of the right ventricle and one directly to the inferior (posterior) leaflet of the tricuspid valve. Variants of the internal anatomy of the heart as exemplified in the present case report should be born in mind during image interpretation and invasive procedures of the right ventricle of the heart.

Determination of a Strain Energy Density Function for the Tricuspid Valve Leaflets Using Constant Invariant-Based Mechanical Characterizations.

The tricuspid valve (TV) regulates the blood flow within the right side of the heart. Despite recent improvements in understanding TV mechanical and microstructural properties, limited attention has been devoted to the development of TV-specific constitutive models. The objective of this work is to use the first-of-its-kind experimental data from constant invariant-based mechanical characterizations to determine a suitable invariant-based strain energy density function (SEDF). Six specimens for each TV leaflet are characterized using constant invariant mechanical testing. The data is then fit with three candidate SEDF forms: (i) a polynomial model-the transversely isotropic version of the Mooney-Rivlin model, (ii) an exponential model, and (iii) a combined polynomial-exponential model. Similar fitting capabilities were found for the exponential and the polynomial forms (R2=0.92-0.99 versus 0.91-0.97) compared to the combined polynomial-exponential SEDF (R2=0.65-0.95). Furthermore, the polynomial form had larger Pearson's correlation coefficients than the exponential form (0.51 versus 0.30), indicating a more well-defined search space. Finally, the exponential and the combined polynomial-exponential forms had notably smaller but more eccentric model parameter's confidence regions than the polynomial form. Further evaluations of invariant decoupling revealed that the decoupling of the invariant terms within the exponential form leads to a less satisfactory performance. From these results, we conclude that the exponential form is better suited for the TV leaflets owing to its superb fitting capabilities and smaller parameter's confidence regions.

A statistical comparison of reproducibility in current pediatric two-dimensional echocardiographic nomograms.

BACKGROUND: The aim of this study is to compare new pediatric nomograms for clinical parameters from 2D echocardiography. METHODS: 2D pediatric echocardiographic parameters from four recent nomograms were used for statistical analysis. To assess the accuracy of the predictive models from each study, namely multivariate, linear, and nonlinear regression, mean values and 5th and 95th percentiles (µ ± 1.65σ) were calculated. A Z-score calculator was created. RESULTS: Mean values and 5th and 95th percentiles have been provided for a range of BSA (0.15-2.20 m2) for each nomogram assessed in this study. Moreover, plots of Z-scores over the same range of BSA have been generated to assess trends among different studies. For most measurements from the two most recent nomograms, namely Lopez et al. and Cantinotti et al., differences were within a Z-score of 0.5 (Z-score range: 0.001-1.26). Measurements from Sluysmans and Colan and Pettersen et al. were observed to diverge from Lopez et al. at the upper extremities of BSA. Differences among various nomograms emerged at lower extremes of BSA. CONCLUSIONS: The two most recent echocardiographic nomograms were observed to have the most statistically similar ranges of normality. Significant deviations in ranges of normality were observed at extremes of BSA. IMPACT: Echocardiographic nomograms for pediatric age are discordant. Comparison of current pediatric echocardiographic nomograms. A Z-score calculator was created. Clinical relevance of differences among nomograms is highlighted.

Quantification of load-dependent changes in the collagen fiber architecture for the strut chordae tendineae-leaflet insertion of porcine atrioventricular heart valves.

Atrioventricular heart valves (AHVs) regulate the unidirectional flow of blood through the heart by opening and closing of the leaflets, which are supported in their functions by the chordae tendineae (CT). The leaflets and CT are primarily composed of collagen fibers that act as the load-bearing component of the tissue microstructures. At the CT-leaflet insertion, the collagen fiber architecture is complex, and has been of increasing focus in the previous literature. However, these previous studies have not been able to quantify the load-dependent changes in the tissue's collagen fiber orientations and alignments. In the present study, we address this gap in knowledge by quantifying the changes in the collagen fiber architecture of the mitral and tricuspid valve's strut CT-leaflet insertions in response to the applied loads by using a unique approach, which combines polarized spatial frequency domain imaging with uniaxial mechanical testing. Additionally, we characterized these microstructural changes across the same specimen without the need for tissue fixatives. We observed increases in the collagen fiber alignments in the CT-leaflet insertion with increased loading, as described through the degree of optical anisotropy. Furthermore, we used a leaflet-CT-papillary muscle entity method during uniaxial testing to quantify the chordae tendineae mechanics, including the derivation of the Ogden-type constitutive modeling parameters. The results from this study provide a valuable insight into the load-dependent behaviors of the strut CT-leaflet insertion, offering a research avenue to better understand the relationship between tissue mechanics and the microstructure, which will contribute to a deeper understanding of AHV biomechanics.

Functional Grading of a Transversely Isotropic Hyperelastic Model with Applications in Modeling Tricuspid and Mitral Valve Transition Regions.

Surgical simulators and injury-prediction human models require a combination of representative tissue geometry and accurate tissue material properties to predict realistic tool-tissue interaction forces and injury mechanisms, respectively. While biological tissues have been individually characterized, the transition regions between tissues have received limited research attention, potentially resulting in inaccuracies within simulations. In this work, an approach to characterize the transition regions in transversely isotropic (TI) soft tissues using functionally graded material (FGM) modeling is presented. The effect of nonlinearities and multi-regime nature of the TI model on the functional grading process is discussed. The proposed approach has been implemented to characterize the transition regions in the leaflet (LL), chordae tendinae (CT) and the papillary muscle (PM) of porcine tricuspid valve (TV) and mitral valve (MV). The FGM model is informed using high resolution morphological measurements of the collagen fiber orientation and tissue composition in the transition regions, and deformation characteristics predicted by the FGM model are numerically validated to experimental data using X-ray diffraction imaging. The results indicate feasibility of using the FGM approach in modeling soft-tissue transitions and has implications in improving physical representation of tissue deformation throughout the body using a scalable version of the proposed approach.

Tricuspid Valve Annuloplasty Alters Leaflet Mechanics.

Tricuspid valve regurgitation is associated with significant morbidity and mortality. Its most common treatment option, tricuspid valve annuloplasty, is not optimally effective in the long-term. Toward identifying the causes for annuloplasty's ineffectiveness, we have previously investigated the technique's impact on the tricuspid annulus and the right ventricular epicardium. In our current work, we are extending our analysis to the anterior tricuspid valve leaflet. To this end, we adopted our previous strategy of performing DeVega suture annuloplasty as an experimental methodology that allows us to externally control the degree of cinching during annuloplasty. Thus, in ten sheep we successively cinched the annulus and quantified changes to leaflet motion, dynamics, and strain in the beating heart by combining sonomicrometry with our well-established mechanical framework. We found that successive cinching of the valve enforced earlier coaptation and thus reduced leaflet range of motion. Additionally, leaflet angular velocity during opening and closing decreased. Finally, we found that leaflet strains were also reduced. Specifically, radial and areal strains decreased as a function of annular cinching. Our findings are critical as they suggest that suture annuloplasty alters the mechanics of the tricuspid valve leaflets which may disrupt their resident cells' mechanobiological equilibrium. Long-term, such disruption may stimulate tissue maladaptation which could contribute to annuloplasty's sub-optimal effectiveness. Additionally, our data suggest that the extent to which annuloplasty alters leaflet mechanics can be controlled via degree of cinching. Hence, our data may provide direct surgical guidelines.

Age-associated changes in 4D flow CMR derived Tricuspid Valvular Flow and Right Ventricular Blood Flow Kinetic Energy.

Assessment of right ventricular (RV) diastolic function is not routinely carried out. This is due to standard two-dimensional imaging techniques being unreliable. Four-dimensional flow (4D flow) derived right ventricular blood flow kinetic energy assessment could circumvent the issues of the current imaging modalities. It also remains unknown whether there is an association between right ventricular blood flow kinetic energy (KE) and healthy ageing. We hypothesise that healthy ageing requires maintaining normal RV intra-cavity blood flow as quantified using KE method. The main objective of this study was to investigate the effect of healthy ageing on tricuspid through-plane flow and right ventricular blood flow kinetic energy. In this study, fifty-three healthy participants received a 4D flow cardiovascular magnetic resonance (CMR) scan on 1.5 T Philips Ingenia. Cine segmentation and 4D flow analysis were performed using dedicated software. Standard statistical methods were carried out to investigate the associations. Both RV E-wave KEiEDV (r = -0.3, P = 0.04) and A-wave KEiEDV (r = 0.42, P < 0.01) showed an association with healthy ageing. Additionally, the right ventricular blood flow KEiEDV E/A ratio demonstrated the strongest association with healthy ageing (r = -0.53, P < 0.01) when compared to all RV functional and haemodynamic parameters. Furthermore, in a multivariate regression model, KEiEDV E/A ratio and 4D flow derived tricuspid valve stroke volume demonstrated independent association to healthy ageing (beta -0.02 and 0.68 respectively, P < 0.01). Ageing is independently associated with 4D flow derived tricuspid stroke volume and RV blood flow KE E/A ratio. These novel 4D flow CMR derived imaging markers have future potential for RV diastolic assessment.

Mechanics of Porcine Heart Valves' Strut Chordae Tendineae Investigated as a Leaflet-Chordae-Papillary Muscle Entity.

Proper blood flow through the atrioventricular heart valves (AHVs) relies on the holistic function of the valve and subvalvular structures, and a failure of any component can lead to life-threatening heart disease. A comprehension of the mechanical characteristics of healthy valvular components is necessary for the refinement of heart valve computational models. In previous studies, the chordae tendineae have been mechanically characterized as individual structures, usually in a clamping-based approach, which may not accurately reflect the in vivo chordal interactions with the leaflet insertion and papillary muscles. In this study, we performed uniaxial mechanical testing of strut chordae tendineae of the AHVs under a unique tine-based leaflet-chordae-papillary muscle testing to observe the chordae mechanics while preserving the subvalvular component interactions. Results of this study provided insight to the disparity of chordae tissue stress-stretch responses between the mitral valve (MV) and the tricuspid valve (TV) under their respective emulated physiological loading. Specifically, strut chordae tendineae of the MV anterior leaflet had peak stretches of 1.09-1.16, while peak stretches of 1.08-1.11 were found for the TV anterior leaflet strut chordae. Constitutive parameters were also derived for the chordae tissue specimens using an Ogden model, which is useful for AHV computational model refinement. Results of this study are beneficial to the eventual improvement of treatment methods for valvular disease.

An investigation of the effect of freezing storage on the biaxial mechanical properties of excised porcine tricuspid valve anterior leaflets.

The atrioventricular heart valve (AHV) leaflets are critical to the facilitation of proper unidirectional blood flow through the heart. Previously, studies have been conducted to understand the tissue mechanics of healthy AHV leaflets to inform the development of valve-specific computational models and replacement materials for use in diagnosing and treating valvular heart disease. Generally, these studies involved biaxial mechanical testing of the AHV leaflet tissue specimens to extract relevant mechanical properties. Most of those studies considered freezing-based storage systems based on previous findings for other connective tissues such as aortic tissue or skin. However, there remains no study that specifically examines the effects of freezing storage on the characterized mechanical properties of the AHV leaflets. In this study, we aimed to address this gap in knowledge by performing biaxial mechanical characterizations of the tricuspid valve anterior leaflet (TVAL) tissue both before and after a 48-h freezing period. Primary findings of this study include: (i) a statistically insignificant change in the tissue extensibilities, with the frozen tissues being slightly stiffer and more anisotropic than the fresh tissues; and (ii) minimal variations in the stress relaxation behaviors between the fresh and frozen tissues, with the frozen tissues demonstrating slightly lessened relaxation. The findings from this study suggested that freezing-based storage does not significantly impact the observed mechanical properties of one of the five AHV leaflets-the TVAL. The results from this study are useful for reaffirming the experimental methodologies in the previous studies, as well as informing the tissue preservation methods of future investigations of AHV leaflet mechanics.

A detailed mechanical and microstructural analysis of ovine tricuspid valve leaflets.

The tricuspid valve ensures unidirectional blood flow from the right atrium to the right ventricle. The three tricuspid leaflets operate within a dynamic stress environment of shear, bending, tensile, and compressive forces, which is cyclically repeated nearly three billion times in a lifetime. Ostensibly, the microstructural and mechanical properties of the tricuspid leaflets have mechanobiologically evolved to optimally support their function under those forces. Yet, how the tricuspid leaflet microstructure determines its mechanical properties and whether this relationship differs between the three leaflets is unknown. Here we perform a microstructural and mechanical analysis in matched ovine tricuspid leaflet samples. We found that the microstructure and mechanical properties vary among the three tricuspid leaflets in sheep. Specifically, we found that tricuspid leaflet composition, collagen orientation, and valve cell nuclear morphology are spatially heterogeneous and vary across leaflet type. Furthermore, under biaxial tension, the leaflets' mechanical behaviors exhibited unequal degrees of mechanical anisotropy. Most importantly, we found that the septal leaflet was stiffer in the radial direction and not the circumferential direction as with the other two leaflets. The differences we observed in leaflet microstructure coincide with the varying biaxial mechanics among leaflets. Our results demonstrate the structure-function relationship for each leaflet in the tricuspid valve. We anticipate our results to be vital toward developing more accurate, leaflet-specific tricuspid valve computational models. Furthermore, our results may be clinically important, informing differential surgical treatments of the tricuspid valve leaflets. Finally, the identified structure-function relationships may provide insight into the homeostatic and remodeling potential of valvular cells in altered mechanical environments, such as in diseased or repaired tricuspid valves. STATEMENT OF SIGNIFICANCE: Our work is significant as we investigated the structure-function relationship of ovine tricuspid valve leaflets. This is important as tricuspid valves fail frequently and our current approach to repairing them is suboptimal. Specifically, we related the distribution of structural and cellular elements, such as collagen, glycosaminoglycans, and cell nuclei, to each leaflet's mechanical properties. We found that leaflets have different structures and that their mechanics differ. This may, in the future, inform leaflet-specific treatment strategies and help optimize surgical outcomes.

An investigation of layer-specific tissue biomechanics of porcine atrioventricular valve anterior leaflets.

Atrioventricular heart valves (AHVs) are composed of structurally complex and morphologically heterogeneous leaflets. The coaptation of these leaflets during the cardiac cycle facilitates unidirectional blood flow. Valve regurgitation is treated preferably by surgical repair if possible or replacement based on the disease state of the valve tissue. A comprehensive understanding of valvular morphology and mechanical properties is crucial to refining computational models, serving as a patient-specific diagnostic and surgical tool for preoperative planning. Previous studies have modeled the stress distribution throughout the leaflet's thickness, but validations with layer-specific biaxial mechanical experiments are missing. In this study, we sought to fill this gap in literature by investigating the impact of microstructure constituents on mechanical behavior throughout the thickness of the AHVs' anterior leaflets. Porcine mitral valve anterior leaflets (MVAL) and tricuspid valve anterior leaflets (TVAL) were micro-dissected into three layers (atrialis/spongiosa, fibrosa, and ventricular) and two layers (atrialis/spongiosa and fibrosa/ventricularis), respectively, based on their relative distributions of extracellular matrix components as quantified by histological analyses: collagen, elastin, and glycosaminoglycans. Our results suggest that (i) for both valves, the atrialis/spongiosa layer is the most extensible and anisotropic layer, possibly due to its relatively low collagen content as compared to other layers, (ii) the intact TVAL response is stiffer than the atrialis/spongiosa layer but more compliant than the fibrosa/ventricularis layer, and (iii) the MVAL fibrosa and ventricularis layers behave nearly isotropic. These novel findings emphasize the biomechanical variances throughout the AHV leaflets, and our results could better inform future AHV computational model developments. STATEMENT OF SIGNIFICANCE: This study, which is the first of its kind for atrioventricular heart valve (AHV) leaflet tissue layers, rendered a mechanical characterization of the biaxial mechanical properties and distributions of extracellular matrix components (collagen, elastin, and glycosaminoglycans) of the mitral and tricuspid valve anterior leaflet layers. The novel findings from the present study emphasize the biomechanical variances throughout the thickness of AHV leaflets, and our results indicate that the previously-adopted homogenous leaflet in the AHV biomechanical modeling may be an oversimplification of the complex leaflet anatomy. Such improvement in the understanding of valvular morphology and tissue mechanics is crucial to future refinement of AHV computational models, serving as a patient-specific diagnostic and surgical tool, at the preoperative stage, for treating valvular heart diseases.

Normal Pediatric Values of the Subcostal Tricuspid Annular Plane Systolic Excursion (S-TAPSE) and Its Value in Pediatric Pulmonary Hypertension.

BACKGROUND: The clinical value of determination of right ventricular (RV) function in adults using echocardiographic determination of the subcostal tricuspid annular plane systolic excursion (S-TAPSE) has previously been reported. We aim to provide representative, normal reference values for S-TAPSE in the pediatric age group. Moreover, validation of abnormal S-TAPSE values in children with impaired RV function, such as pulmonary hypertension (PH), is intended. METHODS: We propose a prospective echocardiographic study in 658 healthy children and in 27 children with PH (age: 1 day to 18 years; BSA 0.2-2.0 m2). We correlated the effects of body surface area (BSA) on S-TAPSE values of our healthy subjects and children with PH. S-TAPSE values were compared with apically derived TAPSE values. RESULTS: S-TAPSE values ranged from a mean of 0.65 ± 0.16 cm in healthy neonates to 1.79 ± 0.33 cm in 18-year-old healthy adolescents. S-TAPSE values increased with increasing age (P = 0.841, P < 0.001), body weight (P = 0.852, P < 0.001), body length (P = 0.846, P < 0.001), and BSA (P = 0.851, P < 0.001) in a nonlinear way in our healthy patients group. No difference in healthy male and female patients could be observed. In our 27 patients with PH (age range: 0.6 to 15.7 years) the median BSA specific S-TAPSE z-score ranged from -3.24 to 1.10, depending on restraint of RV function. CONCLUSION: The provided S-TAPSE normal reference values and z-scores may assist to identify children with impaired RV function. Abnormal S-TAPSE values will help to identify impaired RV function in pediatric patients with PH.

Morpho-functional characterization of the heart of Gallus gallus domesticus with special reference to the right muscular atrioventricular valve.

In this work, we studied the structure and function of the adult chicken heart with a focus on the right muscular atrioventricular valve using anatomic and echocardiographic methods. We demonstrated that the free wall thickness of the right and left ventricles changes from the apex to the base of the heart. The right muscular atrioventricular valve (RAVV) is joined directly to both the parietal right ventricle free wall (one attachment) and the interventricular septum (two attachments: ventral and dorsal). This valve does not have chordae tendineae or papillary muscles. The quantitative morphological and functional characterization of the RAVV is given. In color Doppler echo, no regurgitation of blood flow in the RAVV was observed in any of the studied birds. The blood flow velocity in the RAVV is 56.2 ± 9.6 cm s-1 . A contractile function of the RAVV is shown. Based on the findings obtained, we conclude that the RAVV has a sufficient barrier function. In addition, as this valve is an integral part of the right ventricle free wall, it contributes to the right ventricle pump function. An agreed nomenclature of the parts of the RAVV is required.

Reproducibility of the assessment of myocardial function through tissue Doppler imaging in very low birth weight infants.

OBJECTIVES: This study aims to analyze the variability between two trained neonatologists when performing consecutive echocardiograms using tissue Doppler imaging (TDI) and conventional methods in very low birth weight infant (VLBWI). METHODS: Two serial echocardiograms were performed in 30 VLBWI infants. The echocardiographic parameters analyzed were tricuspid annular plane systolic excursion (TAPSE), A', E', and S' waves, and myocardial performance index acquired by TDI (MPI-TDI) of both ventricles and shortening fraction (SF). The intra-observer and inter-observer agreements and the intra-operator agreement were analyzed using quantitative and qualitative statistical methods. RESULTS: The intra-observer agreement was very good, TAPSE, and TDI-derived parameters had an intra-class correlation (ICC) > 0.8. TDI-derived velocities had a coefficient of variation (COV) < 11%, while MPI-TDI had a COV between 20%-28%. The inter-observer agreement was excellent. There was greater variability when analyzing intra-operator agreement, with the least variable parameter being TAPSE. According to PABAK, the variability presented moderately substantial agreement. CONCLUSIONS: Tricuspid annular plane systolic excursion is very reproducible between observers and operators. Measurements of TDI wave velocities are more reproducible than MPI-TDI. TDI is sufficiently reproducible in the VLBWI if adequate training is performed, and guidelines are followed to obtain standardized echocardiographic images.

Anatomy and Physiology of the Tricuspid Valve.

An appreciation of the complex and variable anatomy of the tricuspid valve is essential to unraveling the pathophysiology of tricuspid regurgitation. A greater appreciation of normal and abnormal anatomy is important as new methods of treating the tricuspid regurgitation are developed. This review of tricuspid valve and right heart anatomy is followed by a discussion of the possible pathophysiology of secondary (functional) tricuspid regurgitation.

Development of a Computational Method for Simulating Tricuspid Valve Dynamics.

Computational modeling can be used to improve understanding of tricuspid valve (TV) biomechanics and supplement knowledge gained from benchtop and large animal experiments. The aim of this study was to develop a computational model of the TV using high resolution micro-computed tomography (µCT) imaging and fluid-structure interaction simulations. A three-dimensional TV model, incorporating detailed leaflet and chordal geometries, was reconstructed from µCT images of an excised porcine TV obtained under diastolic conditions. The leaflets were described using non-linear stress-strain relations and chordal properties were iteratively adjusted until valve closure was obtained. The leaflet coaptation zone obtained from simulation of valve closure was validated against µCT images of the TV captured at peak systole. The computational model was then used to simulate a regurgitant TV morphology and investigate changes in closure dynamics. Overall, the mean stresses in the leaflet belly region and the chordae tendinae of the regurgitant TV were 7% and 3% higher than the same regions of the normal TV. The maximum principal strain in the leaflet belly of the regurgitant TV was also 9% higher than the same regions of the normal TV. It is anticipated that this computational model can be used in future studies for further understanding of TV biomechanics and associated percutaneous repairs.

Right Atrioventricular Valve Leaflet Morphology Redefined: Implications for Transcatheter Repair Procedures.

OBJECTIVES: The authors aimed to comprehensively detail the right atrioventricular valve functional leaflet anatomies. BACKGROUND: The rapid development of both surgical and percutaneous repair techniques for tricuspid regurgitation has renewed interest in variations in the morphology of the right atrioventricular valve. METHODS: The functioning right atrioventricular valves of 40 reanimated human hearts were imaged using Visible Heart methodologies. Hearts were then perfusion-fixed and dissected, uniquely allowing for the comparative assessments of functional versus fixed valve anatomies from the same set of donor hearts. RESULTS: The right atrioventricular valves have "3-leaflet" configurations in 57.5% and "4-leaflet" configurations in the remaining hearts. For 4-leaflet valves, extra leaflets were commonly observed in the most inferior regions of the annuli. No difference in valve perimeters between 2 valve types were observed (112.2 vs. 117.1 mm; p = 0.14). In 3-leaflet valves, septal, mural, and superior leaflets occupied 32.2 ± 6.5%, 15.9 ± 5.5%, and 25.5 ± 6.2% of the annulus, respectively, whereas in the 4-leaflet arrangements, these values were 27.0 ± 5.8% (septal), 12.0 ± 4.5% (inferior), 13.7 ± 9.4% (mural), and 19.8 ± 6.1% (superior). The muroseptal/inferoseptal commissures were usually located in the cavotricuspid regions, whereas the inferomural and superomural commissures were in the right atrial appendage vestibule area. CONCLUSIONS: The right atrioventricular valve has 4 functional leaflets in more than 40% of cases. The authors found that the inferomural region is the most variable area of the valve and believe that anatomic variation is an important consideration for planned interventions.

3-Dimensional Echocardiographic Analysis of the Tricuspid Annulus Provides New Insights Into Tricuspid Valve Geometry and Dynamics.

OBJECTIVES: The authors used transthoracic 3-dimensional transthoracic echocardiography (3DE) to characterize tricuspid annulus (TA) geometry and dynamics in healthy volunteers. BACKGROUND: Accurate sizing of the TA is essential for planning tricuspid annuloplasty and for implantation of new percutaneous tricuspid devices. METHODS: 3DE of the TA from 209 healthy volunteers was analyzed using custom software to measure TA area, perimeter, circularity, and dimensions at end diastole (equals tricuspid valve closure), mid-systole, end systole, and late diastole. TA intercommissural distances were measured at mid-systole. For comparison, TA diameters were measured at the same time points on multiplanar reconstruction of the 3DE datasets and on 2-dimensional transthoracic echocardiography (2DE) apical 4-chamber and right ventricular focused views. In 13 subjects with both 3DE and computed tomography, TA parameters were compared. RESULTS: 3DE TA area, perimeter, and dimensions were largest in late diastole and smallest at mid-systole/end systole. Normal tricuspid valve parameters in end diastole were 8.6 ± 2.0 cm2 for area; 10.5 ± 1.2 cm for perimeter; 36 ± 4 mm and 30 ± 4 mm for longest and shortest dimensions, respectively; and 0.83 ± 0.10 for circularity. There were no age-related changes in TA parameters. Women had larger indexed TA perimeter and longer long-axis dimensions compared with men. The longest 3DE TA dimension was significantly longer than diameters measured from both 2DE and 3D multiplanar reconstruction. 3DE TA area, perimeter, and dimensions correlated with both right atrial and right ventricular volumes, suggesting that both chambers may be determinants of TA size. TA fractional area change was 35 ± 10%. Fractional changes in both perimeter and dimensions were ≥20%. When compared with computed tomography, 3DE systematically underestimated TA parameters. CONCLUSIONS: Gender and body size should be taken into account to identify the reference values of TA dimensions. 2DE underestimates TA dimensions.