Comparative anatomy of the mitral valve in four species (human, ovine, porcine and canine): A pre-clinical perspective

This study aimed to provide comparative anatomical data on the mitral valve and to substantiate the choice between large species for pre-clinical testing of cardiac devices. Different anatomical parameters of the anterior and posterior leaflets, chordae and papillary muscles were measured to characterize the anatomy of the mitral valve in 10 individuals for each four species. Ratios were calculated and used to circumvent the interspecies variations of body and heart size and weight. The results underline many relevant anatomical similarities and differences between man and the three animal species. We confirm that the porcine species is a better model based on anatomical measurements. But many parameters should be considered depending on the shape, size and purpose of the device. The mitral and aortic valve are closer than in man leading to potential damage of the aortic valve by a mitral device. The ovine mitral annulus is more flattened and would sustain more mechanical forces on a round-shaped stent. The anterior and posterior leaflets have comparable height in the animal species leading to more space for implantation. The porcine valve has more chordae allowing less space around the valve for a transcatheter stent. Our observations introduce new comparative data in the perspective of the choice of a large animal model for pre-clinical testing of mitral devices. They are very helpful for all cardiologists, surgeons or engineers who need to understand the reasons for success or failure of a device and to have key elements of discussion.

Anatomical and biometric study of the mitral valve apparatus: application in valve repair surgery

OBJECTIVE

Most mitral valve repair techniques provide excellent surgical results by removing regurgitation, but all of these techniques simultaneously reduce posterior valve mobility. A comprehensive biometric study of the mitral valve apparatus will provide landmarks that would help improve this posterior valve mobility.

MATERIALS AND METHODS

Thirty one (31) human hearts have been studied, from 14 women and 17 men. The characteristics of the studied sample were analyzed descriptively. The difference in means of the variables between women and men were tested using a Student t test. Correlations between the different measures were determined by simple regression analysis. Mean values are shown with ± 1 standard deviation and the limit of significance was set at 0.05.

RESULTS

The mean weight of the hearts was 275.3 ± 2.4 g. The anteroposterior diameter of the mitral annulus was 29.3 ± 1.22 mm, the intertrigonal distance was 25.2 ± 3.50 mm and the anterior leaflet to posterior leaflet ratio was 1.9 ± 0.10, the length of the chordae A2 = 19.4 ± 1.15 mm and P2 = 14.5 ± 0.85 mm. The length of the anterior papillary muscle averaged 30.9 ± 7.20 mm and that of the posterior one 30.0 ± 8.75 mm. The comparison of the different values measured between women and men showed no statistically significant difference (p > 0.05). There was no correlation between these different measured values (p > 0.05).

CONCLUSION

A perfect knowledge of anatomy and biometry is therefore essential to offer alternative techniques that reproduce the real anatomy and physiology with a complete reconstruction of the mitral valve.

Energy loss associated with in-vitro modeling of mitral annular calcification

Introduction

Study aims were to compare hemodynamics and viscous energy dissipation (VED) in 3D printed mitral valves–one replicating a normal valve and the other a valve with severe mitral annular calcification (MAC). Patients with severe MAC develop transmitral gradients, without the commissural fusion typifying rheumatic mitral stenosis (MS), and may have symptoms similar to classical MS. A proposed mechanism relates to VED due to disturbed blood flow through the diseased valve into the ventricle.

Methods

A silicone model of a normal mitral valve (MV) was created using a transesophageal echocardiography dataset. 3D printed calcium phantoms were incorporated into a second valve model to replicate severe MAC. The synthetic MVs were tested in a left heart duplicator under rest and exercise conditions. Fine particles were suspended in a water/glycerol blood analogue for particle image velocimetry calculation of VED.

Results

Catheter mean transmitral gradients were slightly higher in the MAC valve compared to the normal MV, both at rest (3.2 vs. 1.3 mm Hg) and with exercise (5.9 vs. 5.0 mm Hg); Doppler gradients were 2.7 vs. 2.1 mm Hg at rest and 9.9 vs 8.2 mm Hg with exercise. VED was similar between the two valves at rest. During exercise, VED increased to a greater extent for the MAC valve (240%) versus the normal valve (127%).

Conclusion

MAC MS is associated with slightly increased transmitral gradients but markedly increased VED during exercise. These energy losses may contribute to the exercise intolerance and exertional dyspnea present in MAC patients.

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.

Longitudinal Reference Ranges for Tricuspid Annular Plane Systolic Excursion and Mitral Annular Plane Systolic Excursion in Normally Grown Fetuses

OBJECTIVES

The aim of this study was to construct reference ranges for fetal tricuspid annular plane systolic excursion (TAPSE) and mitral annular plane systolic excursion (MAPSE) using conventional M-mode ultrasound (US) in the second half of pregnancy.

METHODS

Participants underwent US scans every 4 weeks from 18 weeks' gestation until delivery. The TAPSE and MAPSE were measured by conventional M-mode US at each examination. The relationships between TAPSE and MAPSE and gestational age and estimated fetal weight were modeled by Bayesian mixed effects linear regression.

RESULTS

Positive linear relationships were observed between both MAPSE and TAPSE and gestational age and estimated fetal weight. Reference centiles for TAPSE and MAPSE were developed.

CONCLUSIONS

This simple technique is a useful tool for assessing cardiac function and could be used for quantitative assessments of fetal cardiac function, particularly in high-risk pregnancies such as those complicated by maternal diabetes.

Reproducibility of Natural Shear Wave Elastography Measurements

For the quantification of myocardial function, myocardial stiffness can potentially be measured non-invasively using shear wave elastography. Clinical diagnosis requires high precision. In 10 healthy volunteers, we studied the reproducibility of the measurement of propagation speeds of shear waves induced by aortic and mitral valve closure (AVC, MVC). Inter-scan was slightly higher but in similar ranges as intra-scan variability (AVC: 0.67 m/s (interquartile range [IQR]: 0.40-0.86 m/s) versus 0.38 m/s (IQR: 0.26-0.68 m/s), MVC: 0.61 m/s (IQR: 0.26-0.94 m/s) versus 0.26 m/s (IQR: 0.15-0.46 m/s)). For AVC, the propagation speeds obtained on different day were not statistically different (p = 0.13). We observed different propagation speeds between 2 systems (AVC: 3.23-4.25 m/s [Zonare ZS3] versus 1.82-4.76 m/s [Philips iE33]), p = 0.04). No statistical difference was observed between observers (AVC: p = 0.35). Our results suggest that measurement inaccuracies dominate the variabilities measured among healthy volunteers. Therefore, measurement precision can be improved by averaging over multiple heartbeats.

Analysis of a coupled fluid-structure interaction model of the left atrium and mitral valve

We present a coupled left atrium-mitral valve model based on computed tomography scans with fibre-reinforced hyperelastic materials. Fluid-structure interaction is realised by using an immersed boundary-finite element framework. Effects of pathological conditions, eg, mitral valve regurgitation and atrial fibrillation, and geometric and structural variations, namely, uniform vs non-uniform atrial wall thickness and rule-based vs atlas-based fibre architectures, on the system are investigated. We show that in the case of atrial fibrillation, pulmonary venous flow reversal at late diastole disappears, and the filling waves at the left atrial appendage orifice during systole have reduced magnitude. In the case of mitral regurgitation, a higher atrial pressure and disturbed flows are seen, especially during systole, when a large regurgitant jet can be found with the suppressed pulmonary venous flow. We also show that both the rule-based and atlas-based fibre defining methods lead to similar flow fields and atrial wall deformations. However, the changes in wall thickness from non-uniform to uniform tend to underestimate the atrial deformation. Using a uniform but thickened wall also lowers the overall strain level. The flow velocity within the left atrial appendage, which is important in terms of appendage thrombosis, increases with the thickness of the left atrial wall. Energy analysis shows that the kinetic and dissipation energies of the flow within the left atrium are altered differently by atrial fibrillation and mitral valve regurgitation, providing a useful indication of the atrial performance in pathological situations.

Modeling the mitral valve

This work is concerned with modeling and simulation of the mitral valve, one of the four valves in the human heart. The valve is composed of leaflets, the free edges of which are supported by a system of chordae, which themselves are anchored to the papillary muscles inside the left ventricle. First, we examine valve anatomy and present the results of original dissections. These display the gross anatomy and information on fiber structure of the mitral valve. Next, we build a model valve following a design-based methodology, meaning that we derive the model geometry and the forces that are needed to support a given load and construct the model accordingly. We incorporate information from the dissections to specify the fiber topology of this model. We assume the valve achieves mechanical equilibrium while supporting a static pressure load. The solution to the resulting differential equations determines the pressurized configuration of the valve model. To complete the model, we then specify a constitutive law based on a stress-strain relation consistent with experimental data that achieves the necessary forces computed in previous steps. Finally, using the immersed boundary method, we simulate the model valve in fluid in a computer test chamber. The model opens easily and closes without leak when driven by physiological pressures over multiple beats. Further, its closure is robust to driving pressures that lack atrial systole or are much lower or higher than normal.

Relationship between geometric changes in mitral annular/leaflets and mitral regurgitation in patients with atrial fibrillation

The objective of the study was to determine the geometric changes in mitral annular and/or leaflets spatial conformation in patients with atrial fibrillation (AF) complicated with severe atrial mitral regurgitation (AMR) by using real-time 3-dimensional transesophageal echocardiography, aiming to explore whether this condition could be improved through self-modulation of mitral annulus and/or leaflets after the restoration of sinus rhythm.Fifty-five patients who were diagnosed with AMR and subject to 1-year follow-up were recruited in this clinical trial. All patients successfully received AF ablation. The intercommissural and anteroposterior diameter, annular height, mitral valve area (MVA), tenting height and volume, annular spherical index, fractional area change of MVA (MVA-FAC), and coaptation index (CP-I) were defined and measured by mitral-valve quantification software. Left ventricular size and function, maximum LA volume (LAV), and LA dimensions were equally recorded.During 1-year follow-up, AMR was significantly decreased in patients with sinus rhythm (P < 0.001). CP-I, MVA-FAC, and LAV index were independently associated with the reduction of AMR.AMR can be improved through the recovery of LAV after ablation, which probably affects the configuration of the annular space and the coaptation of the leaflets.

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.

Modelling mitral valvular dynamics-current trend and future directions

Dysfunction of mitral valve causes morbidity and premature mortality and remains a leading medical problem worldwide. Computational modelling aims to understand the biomechanics of human mitral valve and could lead to the development of new treatment, prevention and diagnosis of mitral valve diseases. Compared with the aortic valve, the mitral valve has been much less studied owing to its highly complex structure and strong interaction with the blood flow and the ventricles. However, the interest in mitral valve modelling is growing, and the sophistication level is increasing with the advanced development of computational technology and imaging tools. This review summarises the state-of-the-art modelling of the mitral valve, including static and dynamics models, models with fluid-structure interaction, and models with the left ventricle interaction. Challenges and future directions are also discussed.

High resolution imaging of the mitral valve in the natural state with 7 Tesla MRI

Imaging techniques of the mitral valve have improved tremendously during the last decade, but challenges persist. The delicate changes in annulus shape and papillary muscle position throughout the cardiac cycle have significant impact on the stress distribution in the leaflets and chords, thus preservation of anatomically accurate positioning is critical. The aim of this study was to develop an in vitro method and apparatus for obtaining high-resolution 3D MRI images of porcine mitral valves in both the diastolic and systolic configurations with physiologically appropriate annular shape, papillary muscle positions and orientations, specific to the heart from which the valve was harvested. Positioning and mounting was achieved through novel, customized mounting hardware consisting of papillary muscle and annulus holders with geometries determined via pre-mortem ultrasonic intra-valve measurements. A semi-automatic process was developed and employed to tailor Computer Aided Design models of the holders used to mount the valve. All valve mounting hardware was 3D printed using a stereolithographic printer, and the material of all fasteners used were brass for MRI compatibility. The mounted valves were placed within a clear acrylic case, capable of holding a zero-pressure and pressurized liquid bath of a MRI-compatible fluid. Obtaining images from the valve submerged in liquid fluid mimics the natural environment surrounding the valve, avoiding artefacts due to tissue surface tension mismatch and gravitational impact on tissue shape when not neutrally buoyant. Fluid pressure was supplied by reservoirs held at differing elevations and monitored and controlled to within ±1mmHg to ensure that the valves remained steady. The valves were scanned in a 7 Tesla MRI system providing a voxel resolution of at least 80μm. The systematic approach produced 3D datasets of high quality which, when combined with physiologically accurate positioning by the apparatus, can serve as an important input for validated computational models.

Fluid-structure interaction and structural analyses using a comprehensive mitral valve model with 3D chordal structure

Over the years, three-dimensional models of the mitral valve have generally been organized around a simplified anatomy. Leaflets have been typically modeled as membranes, tethered to discrete chordae typically modeled as one-dimensional, non-linear cables. Yet, recent, high-resolution medical images have revealed that there is no clear boundary between the chordae and the leaflets. In fact, the mitral valve has been revealed to be more of a webbed structure whose architecture is continuous with the chordae and their extensions into the leaflets. Such detailed images can serve as the basis of anatomically accurate, subject-specific models, wherein the entire valve is modeled with solid elements that more faithfully represent the chordae, the leaflets, and the transition between the two. These models have the potential to enhance our understanding of mitral valve mechanics and to re-examine the role of the mitral valve chordae, which heretofore have been considered to be 'invisible' to the fluid and to be of secondary importance to the leaflets. However, these new models also require a rethinking of modeling assumptions. In this study, we examine the conventional practice of loading the leaflets only and not the chordae in order to study the structural response of the mitral valve apparatus. Specifically, we demonstrate that fully resolved 3D models of the mitral valve require a fluid-structure interaction analysis to correctly load the valve even in the case of quasi-static mechanics. While a fluid-structure interaction mode is still more computationally expensive than a structural-only model, we also show that advances in GPU computing have made such models tractable. Copyright © 2016 John Wiley & Sons, Ltd.

Role of Mitral Annulus Diastolic Geometry on Intraventricular Filling Dynamics

The mitral valve (MV) is a bileaflet valve positioned between the left atrium and ventricle of the heart. The annulus of the MV has been observed to undergo geometric changes during the cardiac cycle, transforming from a saddle D-shape during systole to a flat (and less eccentric) D-shape during diastole. Prosthetic MV devices, including heart valves and annuloplasty rings, are designed based on these two configurations, with the circular design of some prosthetic heart valves (PHVs) being an approximation of the less eccentric, flat D-shape. Characterizing the effects of these geometrical variations on the filling efficiency of the left ventricle (LV) is required to understand why the flat D-shaped annulus is observed in the native MV during diastole in addition to optimizing the design of prosthetic devices. We hypothesize that the D-shaped annulus reduces energy loss during ventricular filling. An experimental left heart simulator (LHS) consisting of a flexible-walled LV physical model was used to characterize the filling efficiency of the two mitral annular geometries. The strength of the dominant vortical structure formed and the energy dissipation rate (EDR) of the measured fields, during the diastolic period of the cardiac cycle, were used as metrics to quantify the filling efficiency. Our results indicated that the O-shaped annulus generates a stronger (25% relative to the D-shaped annulus) vortical structure than that of the D-shaped annulus. It was also found that the O-shaped annulus resulted in higher EDR values throughout the diastolic period of the cardiac cycle. The results support the hypothesis that a D-shaped mitral annulus reduces dissipative energy losses in ventricular filling during diastole and in turn suggests that a symmetric stent design does not provide lower filling efficiency than an equivalent asymmetric design.

Anatomical challenges for transcatheter mitral valve intervention

Following the success of transcatheter aortic and pulmonary valve implantation, there is a large interest in transcatheter mitral valve interventions to treat severe mitral regurgitation (MR). With the exception for the MitraClip™ (Abbott, Abbott Park, IL, USA) edge-to-edge leaflet plication system, most of these transcatheter mitral valve interventions are still in their early clinical or preclinical development phase. Challenges arising from the complex anatomy of the mitral valve and the interplay of the mitral apparatus with the left ventricle (LV) have contributed to a more difficult development process and mixed clinical results with these novel technologies. This review aims to discuss the several anatomical aspects and challenges related to transcatheter mitral valve intervention--the relevant anatomy will be reviewed in relation to specific requirements for device design and procedural aspects of transcatheter mitral valve interventions. To date, experience with these novel therapeutic modalities are still limited and resolution of many challenges are pending. Future studies have to evaluate for whom the transcatheter approach is a feasible and preferred treatment and which patients will benefit from either transcatheter mitral valve repair or replacement. Nevertheless, technological developments are anticipated to drive the transcatheter approach forward into a clinically feasible alternative to surgery for selected patients with severe MR.

Automatic localization of mitral valve orifice in three-dimensional left cardiac model

This study proposes a novel method to localize the mitral valve orifice in the three-dimensional left cardiac model reconstructed from Cardiac Magnetic Resonance (CMR) images. After acquiring both short axis and long axis CMR images, endocardium contours were delineated on all images while additional six points were marked to identify the mitral valve orifice on three long axis images. Contours from long axis images were registered to the short axis contours. The resulting registration parameters were stored. A three-dimensional surface model of the left cardiac structure was then reconstructed from the short axis contours. The six points representing mitral valve orifice in long axis images were projected onto the surface model using the registration parameters. A variational method was then applied to localize the mitral valve orifice on the surface model via minimizing the geodesic distance. Numerical examples show the robustness and effectiveness of the proposed method. Automatic location of mitral annulus orifice with the computational time per data set (22 frames) of five minutes would hold clinical potential as a real-time mitral valve assessment tool.

Distance between the Left Atrial Appendage and Mitral Annulus Evaluated by CARTO 3 Integrated Computed Tomography Imaging

OBJECTIVE

To measure distances between pulmonary veins (PV) and mitral annulus (MA) using angiographic computed tomography (CT) and to compare them with the left atrial appendage-MA (LAA-MA) line.

MATERIALS AND METHODS

Data from 46 catheter ablation procedures for atrial fibrillation involving 36 males, mean age 53 years, range 27-78 years, were analyzed. Three types of mitral isthmus lines were measured using angiographic CT images integrated in the CARTO 3 system (Biosense Webster): the distance between the right superior PV and MA (RSPV-MA), the right inferior PV and MA (RIPV-MA), and the left inferior PV and MA (LIPV-MA). They were compared with the length of the LAA-MA line.

RESULTS

The mean value of LIPV-MA was 29 ± 11.2 mm, RIPV-MA 39 ± 8.2 mm, and RSPV-MA 48 ± 8.2 mm. The circumflex artery (CxA) and the coronary sinus (CS) were closest to the LIPV-MA line. Compared with the three isthmus lines, the LAA-MA was the shortest (24.7 ± 15.6 mm), and the difference was statistically significant (p < 0.05).

CONCLUSION

The angiographic CT provided detailed information regarding the anatomy of the left atrium and distances between atrial structures. The LAA-MA was shorter than the other three lines with the CxA and CS situated at a distance.

A finite strain nonlinear human mitral valve model with fluid-structure interaction

A computational human mitral valve (MV) model under physiological pressure loading is developed using a hybrid finite element immersed boundary method, which incorporates experimentally-based constitutive laws in a three-dimensional fluid-structure interaction framework. A transversely isotropic material constitutive model is used to characterize the mechanical behaviour of the MV tissue based on recent mechanical tests of healthy human mitral leaflets. Our results show good agreement, in terms of the flow rate and the closing and opening configurations, with measurements from in vivo magnetic resonance images. The stresses in the anterior leaflet are found to be higher than those in the posterior leaflet and are concentrated around the annulus trigons and the belly of the leaflet. The results also show that the chordae play an important role in providing a secondary orifice for the flow when the valve opens. Although there are some discrepancies to be overcome in future work, our simulations show that the developed computational model is promising in mimicking the in vivo MV dynamics and providing important information that are not obtainable by in vivo measurements.

Differential and linear insertion of atrioventricular valves: a useful tool?

OBJECTIVE

The differential insertion of the atrioventricular valves is the ultrasonographic representation of the more apical attachment of the tricuspid valve to the septum with respect to the mitral valve. A linear insertion is present when both valves form a linear continuum and has been suggested as a marker for atrioventricular septal defects (AVSDs). The objective of this study was to evaluate the anatomical substratum of differential and linear insertions of the atrioventricular valves in normal fetal hearts and fetal hearts with an AVSD.

METHODS

The extent and position of the fibrous skeleton and attachment of the atrioventricular valves to the septum were studied in histological sections of 17 normal hearts and four hearts with an AVSD from 10 + 0 weeks' gestation to 3 days postpartum with various immunohistochemical tissue markers. In addition, spatiotemporal image correlation (STIC) volumes of 10 normal hearts and STIC volumes of eight hearts with an AVSD at 13 + 6 to 35 + 5 weeks' gestation were examined.

RESULTS

The differential insertion of the atrioventricular valves was visible in normal hearts in the four-chamber plane immediately beneath the aorta, but nearer the diaphragm a linear insertion was found. In hearts with an AVSD, a linear appearance was observed in the four-chamber plane immediately beneath the aorta. Towards the diaphragm, however, first a differential insertion and, more caudally, a linear insertion was found.

CONCLUSIONS

Both differential and linear insertions can be found in normal fetal hearts and fetal hearts with AVSD, depending on the plane in which the four-chamber view is visualized. Therefore, measurement of the differential insertion is likely to be useful only in experienced hands.

Response of functional mitral regurgitation during dobutamine infusion in relation to changes in left ventricular dyssynchrony and mitral valve geometry

PURPOSE

Functional mitral regurgitation (FMR) and myocardial dyssynchrony commonly occur in patients with dilated cardiomyopathy (DCM). The aim of this study was to elucidate changes in FMR in relation to those in left ventricular (LV) dyssynchrony as well as geometric parameters of the mitral valve (MV) in DCM patients during dobutamine infusion.

MATERIALS AND METHODS

Twenty-nine DCM patients (M:F=15:14; age: 62±15 yrs) with FMR underwent echocardiography at baseline and during peak dose (30 or 40 ug/min) of dobutamine infusion. Using 2D echocardiography, LV end-diastolic volume, end-systolic volume (LVESV), ejection fraction (EF), and effective regurgitant orifice area (ERO) were estimated. Dyssynchrony indices (DIs), defined as the standard deviation of time interval-to-peak myocardial systolic contraction of eight LV segments, were measured. Using the multi-planar reconstructive mode from commercially available 3D image analysis software, MV tenting area (MVTa) was measured. All geometrical measurements were corrected (c) by the height of each patient.

RESULTS

During dobutamine infusion, EF (28±8% vs. 39±11%, p=0.001) improved along with significant decrease in cLVESV (80.1±35.2 mm³/m vs. 60.4±31.1 mm³/m, p=0.001); cMVTa (1.28±0.48 cm²/m vs. 0.79±0.33 cm²/m, p=0.001) was significantly reduced; and DI (1.31±0.51 vs. 1.58±0.68, p=0.025) showed significant increase. Despite significant deterioration of LV dyssynchrony during dobutamine infusion, ERO (0.16±0.09 cm² vs. 0.09±0.08 cm², p=0.001) significantly improved. On multivariate analysis, ΔcMVTa and ΔEF were found to be the strongest independent determinants of ΔERO (R²=0.443, p=0.001).

CONCLUSION

Rather than LV dyssynchrony, MV geometry determined by LV geometry and systolic pressure, which represents the MV closing force, may be the primary determinant of MR severity.

Spatial relationship of coronary sinus-great cardiac vein with adjoining anatomic structures: a key element in predicting the success of percutaneous transvenous mitral annuloplasty

BACKGROUND AND AIM OF THE STUDY

Knowledge of the anatomy of the coronary venous system and its relationship with the mitral valve annulus (MVA) and coronary arteries is a key element to successful percutaneous transvenous mitral annuloplasty (PTMA) device implantation for treating patients with severe mitral regurgitation.

METHODS

The spatial relationship of the coronary sinus-great cardiac vein (CS-GCV) with the MVA, left circumflex coronary artery (LCx) and its branches was examined in 120 formalin-fixed adult human cadaveric hearts.

RESULTS

During the initial part of its journey, the CS-GCV was seen to course along and parallel to the plane of the MVA in 109 cases (90.8%), and to cross the MVA obliquely in 11 cases (9.2%). The LCx crossed deep or superficial to the CS-GCV at a discrete point in 98 cases (81.6%) and in eight cases (6.6%), respectively. In two cases (1.6%), the LCx was overlapped by the CS-GCV for an average length of 3.5 +/- 0.7 cm, and in five cases (4.1%) it lay superficial to the CS-GCV for an average length of 3.1 +/- 1.0 cm. In the remaining seven cases (5.8%), the artery did not accompany the CS-GCV along the MVA. Obtuse marginal arteries and the ramus intermedius were seen coursing deep to the CS-GCV in 40 cases (33.3%) and 33 cases (27.5%), respectively.

CONCLUSION

The study results showed that the CS-GCV crosses the annulus obliquely in 9.2% of cases, and hence might affect the efficiency of PTMA. Similarly, positioning of the annuloplasty device in the CS-GCV in cases where the LCx and its branches lay deep to the vein may result in an impingement of the arteries, leading to ischemia.

Numerical simulation of patient-specific left ventricular model with both mitral and aortic valves by FSI approach

Intraventricular flow is important in understanding left ventricular function; however, relevant numerical simulations are limited, especially when heart valve function is taken into account. In this study, intraventricular flow in a patient-specific left ventricle has been modelled in two-dimension (2D) with both mitral and aortic valves integrated. The arbitrary Lagrangian-Eulerian (ALE) approach was employed to handle the large mesh deformation induced by the beating ventricular wall and moving leaflets. Ventricular wall deformation was predefined based on MRI data, while leaflet dynamics were predicted numerically by fluid-structure interaction (FSI). Comparisons of simulation results with in vitro and in vivo measurements reported in the literature demonstrated that numerical method in combination with MRI was able to predict qualitatively the patient-specific intraventricular flow. To the best of our knowledge, we are the first to simulate patient-specific ventricular flow taking into account both mitral and aortic valves.

Ischemic (functional) mitral regurgitation

Mitral regurgitation (MR) is a frequent complication of myocardial infarction and coronary artery disease that is associated with adverse prognosis. The main mechanism of ischemic MR relates to distortion of the spatial relationships between the mitral valve and papillary muscles secondary to ventricular remodeling. The evidence that treatment of ischemic MR improves long-term survival still remains unclear, and further studies are needed to determine whether correcting ischemic MR will improve survival and/or symptoms.

Importance of preservation of chordal apparatus in mitral valve replacement

Mitral valve replacement often involves disruption of the chordal apparatus with disturbance of the annulo-papillary continuity. This results in significant downgrading of ventricular function. Analyzes various reports to accurately assess the advantages of chordal preservation. This review briefly briefly reviews the surgical techniques. The advantages of chordal preservation are analyzed, with particular emphasis on the technical difficulties and potential complications involved.

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

BACKGROUND

The basis of mitral annuloplasty ring design has progressed from qualitative surgical intuition to experimental and theoretical analysis of annular geometry with quantitative imaging techniques. In this work, we present an automated three-dimensional (3D) echocardiographic image analysis method that can be used to statistically assess variability in normal mitral annular geometry to support advancement in annuloplasty ring design.

METHODS

Three-dimensional patient-specific models of the mitral annulus were automatically generated from 3D echocardiographic images acquired from subjects with normal mitral valve structure and function. Geometric annular measurements including annular circumference, annular height, septolateral diameter, intercommissural width, and the annular height to intercommissural width ratio were automatically calculated. A mean 3D annular contour was computed, and principal component analysis was used to evaluate variability in normal annular shape.

RESULTS

The following mean ± standard deviations were obtained from 3D echocardiographic image analysis: annular circumference, 107.0 ± 14.6 mm; annular height, 7.6 ± 2.8 mm; septolateral diameter, 28.5 ± 3.7 mm; intercommissural width, 33.0 ± 5.3 mm; and annular height to intercommissural width ratio, 22.7% ± 6.9%. Principal component analysis indicated that shape variability was primarily related to overall annular size, with more subtle variation in the skewness and height of the anterior annular peak, independent of annular diameter.

CONCLUSIONS

Patient-specific 3D echocardiographic-based modeling of the human mitral valve enables statistical analysis of physiologically normal mitral annular geometry. The tool can potentially lead to the development of a new generation of annuloplasty rings that restore the diseased mitral valve annulus back to a truly normal geometry.

Mitral valve closure prediction with 3-D personalized anatomical models and anisotropic hyperelastic tissue assumptions

This study is concerned with the development of patient-specific simulations of the mitral valve that use personalized anatomical models derived from 3-D transesophageal echocardiography (3-D TEE). The proposed method predicts the closed configuration of the mitral valve by solving for an equilibrium solution that balances various forces including blood pressure, tissue collision, valve tethering, and tissue elasticity. The model also incorporates realistic hyperelastic and anisotropic properties for the valve leaflets. This study compares hyperelastic tissue laws with a quasi-elastic law under various physiological parameters, and provides insights into error sensitivity to chordal placement, allowing for a preliminary comparison of the influence of the two factors (chords and models) on error. Predictive errors show the promise of the method, yielding aggregate median errors of the order of 1 mm, and computed strains and stresses show good correspondence with those reported in prior studies.

Heart sounds: are you listening? Part 2

The first of this two-part article on heart sounds was in the Spring 2013 issue of the Canadian Journal of Cardiovascular Nursing (Reimer-Kent, 2013). Part 1 emphasized the importance of all nurses having an understanding of heart sounds and being proficient in cardiac auscultation. The article also focused on an overview of the fundamentals of cardiac auscultation and basic heart sounds. This article provides an overview of the anatomy and pathophysiology related to valvular heart disease and describes the array of heart sounds associated with stenotic or regurgitant aortic and mitral valve conditions.

Reduced leaflet stress in the stentless quadrileaflet mitral valve: a finite element model

BACKGROUND

Failure of bioprosthetics is usually caused by calcification of the leaflets as a consequence of high tensile stresses. The stentless valve resembles native mitral valve anatomy, has a flexible leaflet attachment and a suspension at the papillary muscles, and preserves annuloventricular continuity. In this study, the effects of the stentless valve design on leaflet stress were investigated with a finite element model.

METHODS

Finite element models of the stentless quadrileaflet mitral valve were created in the close and open configurations. The geometry of the stented trileaflet mitral valve was also analyzed for comparative purposes. Under the designated pressures, the regional stresses were evaluated, and the distributions of stresses were assessed.

RESULTS

Regardless of whether the valve is in the open or close configuration, the maximum first principal stress was significantly lower in the stentless valve than in the stented valve. For the stentless valves, limited stress concentration was discretely distributed in the papillary flaps under both close and open conditions. In contrast, in the stented valve, increased stress concentration was evident at the central belly under the open condition and at the commissural attachment under close condition. In either configuration, the maximum second principal stress was markedly lower in the stentless valve than in the stented valve.

CONCLUSIONS

The stentless valve was associated with a significant reduction in leaflet stress and a more homogeneous stress distribution compared to the stented valve. These findings are consistent with recent reports of the clinical effectiveness of the stentless quadrileaflet mitral valve.

Anatomy, mechanics, and pathophysiology of the mitral annulus

The mitral annulus plays an important role in leaflet coaptation, in unloading mitral valve closing forces, and in promoting left atrial and left ventricular filling and emptying. Perturbations of annular mechanics figure prominently in a number of disorders including functional and ischemic mitral regurgitation, mitral valve prolapse, atrial fibrillation, mitral annular calcification, and annular submitral aneurysm. This review discusses the role of annular dysfunction in the pathogenesis of these disorders.

Structural changes of rat mitral valve chordae tendineae during postnatal development

BACKGROUND AND AIM OF THE STUDY

Mitral valve chordae tendineae are an essential component for correct functioning of the human heart. The microstructural make-up of the chordae is responsible for their tensile properties, and is seen gradually to change with age. However, little is known of the maturation of chordae tendineae and their microstructure.

METHODS

To examine such maturation, structural changes in chordae tendineae were studied in rats at 1, 3, 7, 15 and 30 days of postnatal life, and in adult rats. Differences in the chordae microstructure of each age group were observed using light microscopy. The collagen fibril crimp period was determined using polarized light microscopy.

RESULTS

At day 1 after birth the chordae had yet to develop, and the lateral sides of the mitral valve leaflets were completely attached to the papillary muscles. Chordae developed through the formation of gaps in the leaflet tissue. From day 7 on, numerous chordae were seen. As the chordae matured, crimped collagen fibrils were formed and began to align in a longitudinally packed core with increasing density. The collagen fibril crimp period increased significantly with the age of the animal.

CONCLUSION

Rat chordae tendineae have yet to develop at postnatal day 1. Morphological development and microstructural maturation of the chordae are not completed until adulthood (>30 days). A further understanding of the development of mitral valve chordae tendineae will provide insight for the use of tissue-engineered chordae in surgical repair.

Mitral annular geometry in normal and myxomatous mitral valves: three-dimensional transesophageal echocardiographic quantification

BACKGROUND AND AIM OF THE STUDY

The mitral annulus (MA) has a complex dynamic geometry that is difficult to visualize in two dimensions; hence, novel real-time three-dimensional transesophageal echocardiography (RT-3D-TEE) provides insights into its dynamic nature. The study aim was to investigate changes in MA geometry in normal subjects and to explore differences in patients with myxomatous mitral valve disease (MMVD), using 3D quantitation with RT-3D-TEE.

METHODS

Thirty-five participants (18 with MMVD, 17 normal subjects as controls) were enrolled into the study. The following geometric measurements were obtained at end-systole (ES) and end-diastole (ED): surface area, circumference, perimeter, height, commissure-to-commissure (C-C) diameter, anterior-to-posterior (A-P) diameter, and the ratio of A-P diameter to C-C diameter (circularization). To detect the effect of the severity of mitral regurgitation (MR) on MA dynamics, patients with MMVD were allocated to two subgroups with mild (n = 7) or moderate/severe (n = 11) MR.

RESULTS

Control subjects demonstrated a saddle-shaped, elliptical MA configuration with slightly larger ES parameters. The MA shape was changed during the cardiac cycle, being more circular at ES and flatter at ED (p < 0.05). In MMVD patients, the MA retained a saddle shape but became dilated and circular with larger ED parameters compared to controls (p < 0.05). The degree of MA geometric changes was more prominent in moderate/severe MR patients (p < 0.001), while mild MR patients displayed MA geometry and dynamics similar to those of controls.

CONCLUSION

The MA geometry is altered in MMVD patients, with the extent of changes being determined by the severity of the MR. RT-3D-TEE provides high-quality images that permit a precise quantitative analysis of the 3D geometry of the MA.

On the in vivo deformation of the mitral valve anterior leaflet: effects of annular geometry and referential configuration

Alteration of the native mitral valve (MV) shape has been hypothesized to have a profound effect on the local tissue stress distribution, and is potentially linked to limitations in repair durability. The present study was undertaken to elucidate the relation between MV annular shape and central mitral valve anterior leaflet (MVAL) strain history, using flat annuloplasty in an ovine model. In addition, we report for the first time the presence of residual in vivo leaflet strains. In vivo leaflet deformations were measured using sonocrystal transducers sutured to the MVAL (n = 10), with the 3D positions acquired over the full cardiac cycle. In six animals a flat ring was sutured to the annulus and the transducer positions recorded, while in the remaining four the MV was excised from the exsanguinated heart and the stress-free transducer positions obtained. In the central region of the MVAL the peak stretch values, referenced to the minimum left ventricular pressure (LVP), were 1.10 ± 0.01 and 1.31 ± 0.03 (mean ± standard error) in the circumferential and radial directions, respectively. Following flat ring annuloplasty, the central MVAL contracted 28% circumferentially and elongated 16% radially at minimum LVP, and the circumferential direction was under a negative strain state during the entire cardiac cycle. After valve excision from the exsanguinated heart, the MVAL contracted significantly (18 and 30% in the circumferential and radial directions, respectively), indicating the presence of substantial in vivo residual strains. While the physiological function of the residual strains (and their associated stresses) are at present unknown, accounting for their presence is clearly necessary for accurate computational simulations of MV function. Moreover, we demonstrated that changes in annular geometry dramatically alter valvular functional strains in vivo. As levels of homeostatic strains are related to tissue remodeling and homeostasis, our results suggest that surgically introduced alterations in MV shape could lead to the long term MV mechanobiological and microstructural alterations that could ultimately affect MV repair durability.

Sex variations in the structure of human atrioventricular annuli

Atrioventricular annuli are important in haemodynamic flexibility, competence, and support for tricuspid and mitral valves. The anatomical features of the annuli, such as circumference, organisation of connective tissue fibres, myocardium, and cellularity, may predispose to annular insufficiency and valvular incompetence. These pathologies occur more commonly in females, although the anatomical basis for this disparity is unclear. Sex variation in the structure of the annuli is important in providing a morphological basis for the patterns of these diseases. This study therefore aimed to determine the sex variations in the structure of human atrioventricular annuli. One hundred and one hearts (48 males, 53 females) obtained from the Department of Human Anatomy of the University of Nairobi were studied. Annular circumferences were measured using a flexible ruler and corrected for heart weight. Results were analysed using SPSS version 17.0 and sex differences determined using student's t-test. A p-value of less than 0.05 was considered significant. For light microscopy, specimens were harvested within 48 hours post-mortem, processed, sectioned, and stained with Masson's trichrome and Weigert's elastic stain with van Gieson counterstaining. Females had significantly larger annular circumferences than males after correcting for heart weight (p ≤ 0.05). Histologically, myocardium was consistently present in all male annuli while this was absent in females except in one specimen. The annuli were more elastic and cellular in males especially in the annulo-myocardial and annulo-valvular zones, respectively. The corrected larger annular circumference in females may limit heart valve coaptation during cardiac cycle and may be a risk factor for valvular insufficiency. The predominance of myocardium, annular cellularity, and elasticity may be more protective against heart valve incompetence in males than in females.

[The impact of mitral valve morphology on the short and long-term outcome post percutaneous balloon mitral valvuloplasty in patients with mitral valve stenosis]

OBJECTIVE

To investigate the short and long-term outcome post percutaneous balloon mitral valvuloplasty (PBMV) in mitral valve stenosis patients with different mitral valve morphology.

METHODS

Mitral valve morphology was graded according to the Wilkins scoring system, 385 eligible patients were divided into echocardiographic scores > 8 group (n = 125) and ≤ 8 group (n = 260). Patients were followed up after PBMV according to the improved Inoue method.

RESULTS

PBMV was successful in 370 patients, the success rate of PBMV in > 8 group was significantly lower than in ≤ 8 group (92.8% vs. 97.7%, P < 0.05). Hemodynamic parameters improved significantly in both groups (all P < 0.05) at 6 months post PBMV. Compared to pre-PBMV, improvement on left atrial mean pressure [(14.22 ± 5.02) mm Hg vs. (15.44 ± 5.19) mm Hg (1 mm Hg = 0.133 kPa)], pulmonary artery systolic pressure [(26.13 ± 9.27) mm Hg vs. (31.93 ± 9.98) mm Hg], mitral valve gradient [(9.21 ± 4.11) mm Hg vs. (10.16 ± 4.21) mm Hg] and area of mitral valve orifice [(1.02 ± 0.15) cm(2) vs. (1.20 ± 0.22) cm(2)] post PBMV was less in > 8 group (116 cases) than those in ≤ 8 group (254 cases, all P < 0.05). Three hundreds and fifty three patients were followed up for (78 ± 20) months. Echocardiographic parameters post PBMV improved significantly in both groups compared with the pre-PBMV values during follow-up (all P < 0.05). However, left atrial mean pressure, pulmonary artery systolic pressure, mitral valve gradient and area of mitral valve orifice in > 8 group (108 cases) improved less than those in ≤ 8 group (245 cases) [(13.28 ± 5.06) mm Hg vs. (14.77 ± 5.17) mm Hg, (21.19 ± 9.17) mm Hg vs. (28.92 ± 9.91) mm Hg, (7.30 ± 4.40) mm Hg vs. (9.16 ± 4.28) mm Hg, (0.92 ± 0.17) cm(2) vs. (1.07 ± 0.20) cm(2); all P < 0.05]. The incidence of mitral restenosis was also significantly higher in > 8 group than in ≤ 8 group (20.4% vs. 8.2%, P < 0.05).

CONCLUSIONS

The mitral valve morphology played a key role on the outcome post PBMV in patients with mitral valve stenosis. Patients with lower echocardiographic scores benefit more from PBMV than patients with higher echocardiographic scores.

In vivo dynamic strains of the ovine anterior mitral valve leaflet

Understanding the mechanics of the mitral valve is crucial in terms of designing and evaluating medical devices and techniques for mitral valve repair. In the current study we characterize the in vivo strains of the anterior mitral valve leaflet. On cardiopulmonary bypass, we sew miniature markers onto the leaflets of 57 sheep. During the cardiac cycle, the coordinates of these markers are recorded via biplane fluoroscopy. From the resulting four-dimensional data sets, we calculate areal, maximum principal, circumferential, and radial leaflet strains and display their profiles on the averaged leaflet geometry. Average peak areal strains are 13.8±6.3%, maximum principal strains are 13.0±4.7%, circumferential strains are 5.0±2.7%, and radial strains are 7.8±4.3%. Maximum principal strains are largest in the belly region, where they are aligned with the circumferential direction during diastole switching into the radial direction during systole. Circumferential strains are concentrated at the distal portion of the belly region close to the free edge of the leaflet, while radial strains are highest in the center of the leaflet, stretching from the posterior to the anterior commissure. In summary, leaflet strains display significant temporal, regional, and directional variations with largest values inside the belly region and toward the free edge. Characterizing strain distribution profiles might be of particular clinical significance when optimizing mitral valve repair techniques in terms of forces on suture lines and on medical devices.

["Right hand" mitral valve model: a simple and free model available at anywhere]

We have devised a simple and cost-free mitral valve model using "right hand", which is placed on the median portion of anterior chest and supinated by 30 degrees. The palm is used to resemble the mitral valve:the thenar eminence, its margin wrinkle, and adjacent palm as the anterior leaflet, coaptation line, and the posterior leaflet, respectively. As the thumb and its origin is assumed as the ascending aorta and aortic valve, this model represents the mitral and aortic valves as viewed from the left atrium. This model is anatomically accurate and facilitates comprehending image orientation in transesophageal echocardiographic probe manipulations.

Mitral valvular interstitial cell responses to substrate stiffness depend on age and anatomic region

The material properties of heart valves depend on the subject's age, the state of the disease and the complex valvular microarchitecture. Furthermore, valvular interstitial cells (VICs) are mechanosensitive, and their synthesis of extracellular matrix not only determines the valve's material properties but also provides an adhesive substrate for VICs. However, the interrelationship between substrate stiffness and VIC phenotype and synthetic properties is poorly understood. Given that the local mechanical environment (substrate stiffness) surrounding VICs differs among different age groups and different anatomic regions of the valve, it was hypothesized that there may be an age- and valve-region-specific response of VICs to substrate stiffness. Therefore, 6-week-, 6-month- and 6-year-old porcine VICs from the center of the mitral valve anterior leaflet (MVAC) and posterior leaflet (PML) were seeded onto poly(ethylene) glycol hydrogels of different stiffnesses and stained for markers of VIC activation (smooth muscle alpha-actin (SMaA)) and collagen synthesis (heat shock protein-47 (HSP47), prolyl 4-hydroxylase (P4H)). Six-week-old MVAC demonstrated decreased SMaA, P4H and HSP47 on stiffer gels, while 6-week-old PML only demonstrated decreased HSP47. Six-month-old MVAC demonstrated no difference between substrates, while 6-month-old PML demonstrated decreased SMaA, P4H and HSP47. Six-year-old MVAC demonstrated decreased P4H and HSP47, while 6-year-old PML demonstrated decreased P4H and increased HSP47. In conclusion, the age-specific and valve-region-specific responses of VICs to substrate stiffness link VIC phenotype to the leaflet regional matrix in which the VICs reside. These data provide further rationale for investigating the role of substrate stiffness in VIC remodeling within diseased and tissue engineered valves.

Anterior mitral leaflet curvature during the cardiac cycle in the normal ovine heart

BACKGROUND

The dynamic changes of anterior mitral leaflet (AML) curvature are of primary importance for optimal left ventricular filling and emptying but are incompletely characterized.

METHODS AND RESULTS

Sixteen radiopaque markers were sutured to the AML in 11 sheep, and 4-dimensional marker coordinates were acquired with biplane videofluoroscopy. A surface subdivision algorithm was applied to compute the curvature across the AML at midsystole and at maximal valve opening. Septal-lateral (SL) and commissure-commissure (CC) curvature profiles were calculated along the SL AML meridian (M(SL))and CC AML meridian (M(CC)), respectively, with positive curvature being concave toward the left atrium. At midsystole, the M(SL) was concave near the mitral annulus, turned from concave to convex across the belly, and was convex along the free edge. At maximal valve opening, the M(SL) was flat near the annulus, turned from slightly concave to convex across the belly, and flattened toward the free edge. In contrast, the M(CC) was concave near both commissures and convex at the belly at midsystole but convex near both commissures and concave at the belly at maximal valve opening.

CONCLUSIONS

While the SL curvature of the AML along the M(SL) is similar across the belly region at midsystole and early diastole, the CC curvature of the AML along the M(CC) flips, with the belly being convex to the left atrium at midsystole and concave at maximal valve opening. These curvature orientations suggest optimal left ventricular inflow and outflow shapes of the AML and should be preserved during catheter or surgical interventions.

Mitral annulus segmentation from 3D ultrasound using graph cuts

The shape of the mitral valve annulus is used in diagnostic and modeling applications, yet methods to accurately and reproducibly delineate the annulus are limited. This paper presents a mitral annulus segmentation algorithm designed for closed mitral valves which locates the annulus in three-dimensional ultrasound using only a single user-specified point near the center of the valve. The algorithm first constructs a surface at the location of the thin leaflets, and then locates the annulus by finding where the thin leaflet tissue meets the thicker heart wall. The algorithm iterates until convergence metrics are satisfied, resulting in an operator-independent mitral annulus segmentation. The accuracy of the algorithm was assessed from both a diagnostic and surgical standpoint by comparing the algorithm's results to delineations made by a group of experts on clinical ultrasound images of the mitral valve, and to delineations made by an expert with a surgical view of the mitral annulus on excised porcine hearts using an electromagnetically tracked pointer. In the former study, the algorithm was statistically indistinguishable from the best performing expert (p=0.85) and had an average RMS difference of 1.81+/-0.78 mm to the expert average. In the latter, the average RMS difference between the algorithm's annulus and the electromagnetically tracked points across six hearts was 1.19+/-0.17 mm .

Patient-specific modeling and quantification of the aortic and mitral valves from 4-D cardiac CT and TEE

As decisions in cardiology increasingly rely on noninvasive methods, fast and precise image processing tools have become a crucial component of the analysis workflow. To the best of our knowledge, we propose the first automatic system for patient-specific modeling and quantification of the left heart valves, which operates on cardiac computed tomography (CT) and transesophageal echocardiogram (TEE) data. Robust algorithms, based on recent advances in discriminative learning, are used to estimate patient-specific parameters from sequences of volumes covering an entire cardiac cycle. A novel physiological model of the aortic and mitral valves is introduced, which captures complex morphologic, dynamic, and pathologic variations. This holistic representation is hierarchically defined on three abstraction levels: global location and rigid motion model, nonrigid landmark motion model, and comprehensive aortic-mitral model. First we compute the rough location and cardiac motion applying marginal space learning. The rapid and complex motion of the valves, represented by anatomical landmarks, is estimated using a novel trajectory spectrum learning algorithm. The obtained landmark model guides the fitting of the full physiological valve model, which is locally refined through learned boundary detectors. Measurements efficiently computed from the aortic-mitral representation support an effective morphological and functional clinical evaluation. Extensive experiments on a heterogeneous data set, cumulated to 1516 TEE volumes from 65 4-D TEE sequences and 690 cardiac CT volumes from 69 4-D CT sequences, demonstrated a speed of 4.8 seconds per volume and average accuracy of 1.45 mm with respect to expert defined ground-truth. Additional clinical validations prove the quantification precision to be in the range of inter-user variability. To the best of our knowledge this is the first time a patient-specific model of the aortic and mitral valves is automatically estimated from volumetric sequences.

3D velocity quantification in the heart: improvements by 3D PC-SSFP

PURPOSE

To test whether a 3D imaging sequence with phase contrast (PC) velocity encoding based on steady-state free precession (SSFP) improves 3D velocity quantification in the heart compared to the currently available gradient echo (GE) approach.

MATERIALS AND METHODS

The 3D PC-SSFP sequence with 1D velocity encoding was compared at the mitral valve in 12 healthy subjects with 3D PC-GE at 1.5T. Velocity measurements, velocity-to-noise-ratio efficiency (VNR(eff)), intra- and interobserver variability of area and velocity measurements, contrast-to-noise-ratio (CNR), and artifact sensitivity were evaluated in both long- and short-axis orientation.

RESULTS

Descending aorta mean and peak velocities correlated well (r(2) = 0.79 and 0.93) between 3D PC-SSFP and 3D PC-GE. At the mitral valve, mean velocity correlation was moderate (r(2) = 0.70 short axis, 0.56 long axis) and peak velocity showed good correlation (r(2) = 0.94 short axis, 0.81 long axis). In some cases VNR(eff) was higher, in others lesser, depending on slab orientation and cardiac phase. Intra- and interobserver variability was generally better for 3D PC-SSFP. CNR improved significantly, especially at end systole. Artifact levels did not increase.

CONCLUSION

3D SSFP velocity quantification was successfully tested in the heart. Blood-myocardium contrast improved significantly, resulting in more reproducible velocity measurements for 3D PC-SSFP at 1.5T.

Functional anatomy of normal mitral valve-left ventricular complex by real-time, three-dimensional echocardiography

BACKGROUND AND AIM OF THE STUDY

A detailed anatomic examination of the mitral valve (MV)-left ventricular (LV) complex (annulus, leaflets, chordae, papillary muscles, and ventricular wall) is needed for the accurate assessment of functional mitral regurgitation, and for planning patient-specific valve repair. In the past, normal values for the various components of the MV-LV complex have been derived from two-dimensional echocardiography (2DE), but such measurements require unconventional image planes and allow no off-line adjustments. In addition, measurement of the LV volumes and dimensions of irregular structures (mitral annulus) is more accurate by using three-dimensional echocardiography (3DE). The study aim was to assess, quantitatively, the MV-LV complex by real-time 3DE in normal adults.

METHODS

The components of the MV-LV complex were measured off-line at mid-diastole (anterior MV leaflet), end-diastole and end-systole, after full volume real-time 3DE data sets had been obtained using a matrix transducer in 10 normal adults (six females, four males; mean age 25 +/- 5 years; range: 18-35 years; mean body surface area 1.8 +/- 0.2 m2). 2DE measurements were made for comparison.

RESULTS

The 2DE measurements were systematically smaller (1-12%) than 3DE measurements, due to a foreshortening of the various components of the MV-LV complex during 2DE imaging. By 3DE imaging, MV competence in normal hearts was achieved by systolic reduction in the LV volume (58%), LV length (17%), inter-papillary muscle distance (39%), annular diameter (6% anteroposterior, 14% mediolateral), and the length of both papillary muscles (21-31%). At end-systole, the anterior MV leaflet was 20% shorter (2.5 +/- 0.3 versus 2.0 +/- 0.3 cm), due to folding at the coaptation point.

CONCLUSION

These data provide normal real-time 3DE reference values for the MV-LV complex. 3DE appears superior to 2DE for accurate functional assessment of the MV-LV complex.

Contemporary insights into the functional anatomy of the mitral valve

The mitral valve is a highly complex structure the normal functioning of which requires the coordinated interaction of the leaflets, annulus, chordae tendineae, and papillary muscles. Perturbations of any of these components can interfere with normal valve function. The integrity of the mitral valve is also essential to maintaining normal left ventricular geometry and function through closely coupled ventricular-valvular interactions. This review summarizes recent developments in our understanding of the anatomy and physiology of the mitral valve.