In vitro mitral valve simulator mimics systolic valvular function of chronic ischemic mitral regurgitation ovine model

An Anatomically Shaped Mitral Valve for Hemodynamic Testing

In vitro modeling of the left heart relies on accurately replicating the physiological conditions of the native heart. The targeted physiological conditions include the complex fluid dynamics coming along with the opening and closing of the aortic and mitral valves. As the mitral valve possess a highly sophisticated apparatus, thence, accurately modeling it remained a missing piece in the perfect heart duplicator puzzle. In this study, we explore using a hydrogel-based mitral valve that offers a full representation of the mitral valve apparatus. The valve is tested using a custom-made mock circulatory loop to replicate the left heart. The flow analysis includes performing particle image velocimetry measurements in both left atrium and ventricle. The results showed the ability of the new mitral valve to replicate the real interventricular and atrial flow patterns during the whole cardiac cycle. Moreover, the investigated valve has a ventricular vortex formation time of 5.2, while the peak e- and a-wave ventricular velocities was 0.9 m/s and 0.4 m/s respectively.

Influence of Dorper lamb development from birth to 120 days of age on clinical and echocardiographic parameters

The expansion of the sheep model in research represents an attractive and economically beneficial academic reason for investigations in sheep echocardiography. The present study aimed to evaluate the clinical and echocardiographic parameters in Dorper lambs during the developmental period. Emphasis was placed on the use of the species in translational research for the echocardiographic diagnosis of congenital heart diseases, which can contribute to improvements in interventionist techniques. Ten Dorper lambs were evaluated at the following time points: 24 h after birth and 7, 14, 21, 30, 60, 90 and 120 days of age. Clinical parameters were compiled, and echocardiogram records were obtained without sedation. Rectal temperature was lower on the first day compared to the others. From 21 days of life, there was a reduction in HR, with differences between time points. Mean and systolic blood pressure differed, with the highest values at 90 and 120 days of age. The thickness of the interventricular septum in diastole (IVSd) increased as age progressed, with the highest value at 120 days of age, and the same occurred for LVIDd (left ventricle internal diameter in diastole), LVFWd (left ventricular free wall thickness in diastole), IVSs (interventricular septum thickness in systole), LVIDs (left ventricle internal diameter in systole) and LVFWs (left ventricular free wall thickness in systole). There were differences in the size of the LA, Ao and LA/Ao ratio, which were greater at 90 days and 120 days of age. Echocardiographic changes accompany the development of lambs, where changes in echocardiographic parameters are evident with advancing age. The echocardiographic measurements in lambs obtained in the present study are similar to those in newborns.

In Vitro Mitral Valve Model with Unrestricted Ventricular Access: Using Vacuum to Close the Valve and Enable Static Trans-Mitral Pressure

Current in vitro models of the left heart establish the pressure difference required to close the mitral valve by sealing and pressurizing the ventricular side of the valve, limiting important access to the subvalvular apparatus. This paper describes and evaluates a system that establishes physiological pressure differences across the valve using vacuum on the atrial side. The subvalvular apparatus is open to atmospheric pressure and accessible by tools and sensors, establishing a novel technique for experimentation on atrioventricular valves. Porcine mitral valves were excised and closed by vacuum within the atrial chamber. Images were used to document and analyze closure of the leaflets. Papillary muscle force and regurgitant flow rate were measured to be 4.07 N at 120 mmHg and approximately 12.1 ml/s respectively, both of which are within clinically relevant ranges. The relative ease of these measurements demonstrates the usefulness of improved ventricular access at peak pressure/force closure.

A Novel Quantitative Ex Vivo Model of Functional Mitral Regurgitation

OBJECTIVE

Durability of mitral valve (MV) repair for functional mitral regurgitation (FMR) remains suboptimal. We sought to create a highly reproducible, quantitative ex vivo model of FMR that functions as a platform to test novel repair techniques.

METHODS

Fresh swine hearts (n = 10) were pressurized with air to a left ventricular pressure of 120 mmHg. The left atrium was excised and the altered geometry of FMR was created by radially dilating the annulus and displacing the papillary muscle tips apically and radially in a calibrated fashion. This was continued in a graduated fashion until coaptation was exhausted. Imaging of the MV was performed with a 3-dimensional (3D) structured-light scanner, which records 3D structure, texture, and color. The model was validated using transesophageal echocardiography in patients with normal MVs and severe FMR.

RESULTS

Compared to controls, the anteroposterior diameter in the FMR state increased 32% and the annular area increased 35% (P < 0.001). While the anterior annular circumference remained fixed, the posterior circumference increased by 20% (P = 0.026). The annulus became more planar and the tenting height increased 56% (9 to 14 mm, P < 0.001). The median coaptation depth significantly decreased (anterior leaflet: 5 vs 2 mm; posterior leaflet: 7 vs 3 mm, P < 0.001). The ex vivo normal and FMR models had similar characteristics as clinical controls and patients with severe FMR.

CONCLUSIONS

This novel quantitative ex vivo model provides a simple, reproducible, and inexpensive benchtop representation of FMR that mimics the systolic valvular changes of patients with FMR.

A noninvasive method for the determination of in vivo mitral valve leaflet strains

Assessment of mitral valve (MV) function is important in many diagnostic, prognostic, and surgical planning applications for treatment of MV disease. Yet, to date, there are no accepted noninvasive methods for determination of MV leaflet deformation, which is a critical metric of MV function. In this study, we present a novel, completely noninvasive computational method to estimate MV leaflet in-plane strains from clinical-quality real-time three-dimensional echocardiography (rt-3DE) images. The images were first segmented to produce meshed medial-surface leaflet geometries of the open and closed states. To establish material point correspondence between the two states, an image-based morphing pipeline was implemented within a finite element (FE) modeling framework in which MV closure was simulated by pressurizing the open-state geometry, and local corrective loads were applied to enforce the actual MV closed shape. This resulted in a complete map of local systolic leaflet membrane strains, obtained from the final FE mesh configuration. To validate the method, we utilized an extant in vitro database of fiducially labeled MVs, imaged in conditions mimicking both the healthy and diseased states. Our method estimated local anisotropic in vivo strains with less than 10% error and proved to be robust to changes in boundary conditions similar to those observed in ischemic MV disease. Next, we applied our methodology to ovine MVs imaged in vivo with rt-3DE and compared our results to previously published findings of in vivo MV strains in the same type of animal as measured using surgically sutured fiducial marker arrays. In regions encompassed by fiducial markers, we found no significant differences in circumferential(P = 0.240) or radial (P = 0.808) strain estimates between the marker-based measurements and our novel noninvasive method. This method can thus be used for model validation as well as for studies of MV disease and repair.

Impact of simulated MitraClip on forward flow obstruction in the setting of mitral leaflet tethering: An in vitro investigation

OBJECTIVES

We aimed to evaluate diastolic leaflet tethering as a factor that may cause mitral stenosis (MS) after simulated MitraClip implantation, using an in vitro left heart simulator.

BACKGROUND

Leaflet tethering commonly seen in functional mitral regurgitation may be a significant factor affecting the severity of MS after MitraClip implantation.

METHODS

A left heart simulator with excised ovine mitral valves (N = 6), and custom edge-to-edge clip devices (GTclip) was used to mimic implantation of MitraClip in a variety of positions. Anterior mitral leaflet (AML) tethering severity was varied for each case (leaflet excursion of 75°, 60°, and 45°, consistent with mild, moderate and severe tethering), and the baseline mitral annular area (MAA) was varied across samples (3.6-4.8 cm² ). The resulting mitral valve area (MVA), and peak/mean mitral valve gradient (MVG) were measured in each case.

RESULTS

AML tethering severity was a highly significant factor increasing MVG and decreasing MVA (P < 0.001). When GTclip placement was simulated with severe AML tethering, mean MVG >5 mmHg resulted more frequently than with GTclip placement alone (46% vs. 4%, respectively). However, severe AML tethering alone significantly reduced baseline MVA to 3.6 ± 0.2 cm² , and increased baseline MVG to 3.0 ± 0.4 mmHg. At MAA above 4.7 cm² , severe AML tethering did not cause moderate MS, even with placement of two GTclips (95% confidence).

CONCLUSIONS

Our results show that diastolic AML tethering may predispose to MS after clip placement, however, MS was not observed when baseline MVA was above 4.0 cm² . Severity of AML tethering may be an important criterion in selecting patients for edge-to-edge repair.

Realistic Vascular Replicator for TAVR Procedures

Transcatheter aortic valve replacement (TAVR) is an over-the-wire procedure for treatment of severe aortic stenosis (AS). TAVR valves are conventionally tested using simplified left heart simulators (LHS). While those provide baseline performance reliably, their aortic root geometries are far from the anatomical in situ configuration, often overestimating the valves' performance. We report on a novel benchtop patient-specific arterial replicator designed for testing TAVR and training interventional cardiologists in the procedure. The Replicator is an accurate model of the human upper body vasculature for training physicians in percutaneous interventions. It comprises of fully-automated Windkessel mechanism to recreate physiological flow conditions. Calcified aortic valve models were fabricated and incorporated into the Replicator, then tested for performing TAVR procedure by an experienced cardiologist using the Inovare valve. EOA, pressures, and angiograms were monitored pre- and post-TAVR. A St. Jude mechanical valve was tested as a reference that is less affected by the AS anatomy. Results in the Replicator of both valves were compared to the performance in a commercial ISO-compliant LHS. The AS anatomy in the Replicator resulted in a significant decrease of the TAVR valve performance relative to the simplified LHS, with EOA and transvalvular pressures comparable to clinical data. Minor change was seen in the mechanical valve performance. The Replicator showed to be an effective platform for TAVR testing. Unlike a simplified geometric anatomy LHS, it conservatively provides clinically-relevant outcomes and complement it. The Replicator can be most valuable for testing new valves under challenging patient anatomies, physicians training, and procedural planning.

A comprehensive pipeline for multi-resolution modeling of the mitral valve: Validation, computational efficiency, and predictive capability

Multiple studies have demonstrated that the pathological geometries unique to each patient can affect the durability of mitral valve (MV) repairs. While computational modeling of the MV is a promising approach to improve the surgical outcomes, the complex MV geometry precludes use of simplified models. Moreover, the lack of complete in vivo geometric information presents significant challenges in the development of patient-specific computational models. There is thus a need to determine the level of detail necessary for predictive MV models. To address this issue, we have developed a novel pipeline for building attribute-rich computational models of MV with varying fidelity directly from the in vitro imaging data. The approach combines high-resolution geometric information from loaded and unloaded states to achieve a high level of anatomic detail, followed by mapping and parametric embedding of tissue attributes to build a high-resolution, attribute-rich computational models. Subsequent lower resolution models were then developed and evaluated by comparing the displacements and surface strains to those extracted from the imaging data. We then identified the critical levels of fidelity for building predictive MV models in the dilated and repaired states. We demonstrated that a model with a feature size of about 5 mm and mesh size of about 1 mm was sufficient to predict the overall MV shape, stress, and strain distributions with high accuracy. However, we also noted that more detailed models were found to be needed to simulate microstructural events. We conclude that the developed pipeline enables sufficiently complex models for biomechanical simulations of MV in normal, dilated, repaired states.

Effects of annular contraction on anterior leaflet strain using an in vitro simulator with a dynamically contracting mitral annulus

Using in vitro models, the mechanics as well as surgical techniques for mitral valves (MV) and MV devices can be studied in a more controlled environment with minimal monetary investment and risk. However, these current models rely on certain simplifications, one being that the MV has a static, rigid annulus. In order to study more complex issues of imaging diagnostics and implanted device function, it would be more advantageous to verify their use for a dynamic environment in a dynamic simulator. This study provides the novel design and development of a dynamically contracting annulus (DCA) within an in vitro simulator, and its subsequent use to study MV biomechanics. Experiments were performed to study the ability of the DCA to reproduce the MV leaflet mechanics in vitro, as seen in vivo, as well as investigate how rigid annuloplasties affect MV leaflet mechanics. Experiments used healthy, excised MVs and normal hemodynamics; contractile waveforms were derived from human in vivo data. Stereophotogrammetry and echocardiography were used to measure anterior leaflet strain and the change in MV geometry. In pursuit of the first in vitro MV simulator that more completely represents the dynamic motion of the full valvular apparatus, this study demonstrated the successful operation of a dynamically contracting mitral annulus. It was seen that the diseased contractile state increased anterior leaflet strain compared to the healthy contractile state. In addition, it was also shown in vitro that simulated rigid annuloplasty increased mitral anterior leaflet strain compared to a healthy contraction.

Multi-resolution geometric modeling of the mitral heart valve leaflets

An essential element of cardiac function, the mitral valve (MV) ensures proper directional blood flow between the left heart chambers. Over the past two decades, computational simulations have made marked advancements toward providing powerful predictive tools to better understand valvular function and improve treatments for MV disease. However, challenges remain in the development of robust means for the quantification and representation of MV leaflet geometry. In this study, we present a novel modeling pipeline to quantitatively characterize and represent MV leaflet surface geometry. Our methodology utilized a two-part additive decomposition of the MV geometric features to decouple the macro-level general leaflet shape descriptors from the leaflet fine-scale features. First, the general shapes of five ovine MV leaflets were modeled using superquadric surfaces. Second, the finer-scale geometric details were captured, quantified, and reconstructed via a 2D Fourier analysis with an additional sparsity constraint. This spectral approach allowed us to easily control the level of geometric details in the reconstructed geometry. The results revealed that our methodology provided a robust and accurate approach to develop MV-specific models with an adjustable level of spatial resolution and geometric detail. Such fully customizable models provide the necessary means to perform computational simulations of the MV at a range of geometric accuracies in order to identify the level of complexity required to achieve predictive MV simulations.

Ex Vivo Methods for Informing Computational Models of the Mitral Valve

Computational modeling of the mitral valve (MV) has potential applications for determining optimal MV repair techniques and risk of recurrent mitral regurgitation. Two key concerns for informing these models are (1) sensitivity of model performance to the accuracy of the input geometry, and, (2) acquisition of comprehensive data sets against which the simulation can be validated across clinically relevant geometries. Addressing the first concern, ex vivo micro-computed tomography (microCT) was used to image MVs at high resolution (~40 micron voxel size). Because MVs distorted substantially during static imaging, glutaraldehyde fixation was used prior to microCT. After fixation, MV leaflet distortions were significantly smaller (p < 0.005), and detail of the chordal tree was appreciably greater. Addressing the second concern, a left heart simulator was designed to reproduce MV geometric perturbations seen in vivo in functional mitral regurgitation and after subsequent repair, and maintain compatibility with microCT. By permuting individual excised ovine MVs (n = 5) through each state (healthy, diseased and repaired), and imaging with microCT in each state, a comprehensive data set was produced. Using this data set, work is ongoing to construct and validate high-fidelity MV biomechanical models. These models will seek to link MV function across clinically relevant states.

Mitral Valve Chordae Tendineae: Topological and Geometrical Characterization

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

Three-Dimensional Field Optimization Method: Gold-Standard Validation of a Novel Color Doppler Method for Quantifying Mitral Regurgitation

BACKGROUND

Accurate diagnosis of mitral regurgitation (MR) severity is central to proper treatment. Although numerous approaches exist, an accurate, gold-standard clinical technique remains elusive. The authors previously reported on the initial development and demonstration of the automated three-dimensional (3D) field optimization method (FOM) algorithm, which exploits 3D color Doppler ultrasound imaging and builds on existing MR quantification techniques. The aim of the present study was to extensively validate 3D FOM in terms of accuracy, ease of use, and repeatability.

METHODS

Three-dimensional FOM was applied to five explanted ovine mitral valves in a left heart simulator, which were systematically perturbed to yield a total of 29 unique regurgitant geometries. Three-dimensional FOM was compared with a gold-standard flow probe, as well as the most clinically prevalent MR volume quantification technique, the two-dimensional (2D) proximal isovelocity surface area (PISA) method.

RESULTS

Overall, 3D FOM overestimated and 2D PISA underestimated MR volume, but 3D FOM error had smaller magnitude (5.2 ± 9.9 mL) than 2D PISA error (-6.9 ± 7.7 mL). Two-dimensional PISA remained superior in diagnosis for round orifices and especially mild MR, as predicted by ultrasound physics theory. For slit-type orifices and severe MR, 3D FOM showed significant improvement over 2D PISA. Three-dimensional FOM processing was technically simpler and significantly faster than 2D PISA and required fewer ultrasound acquisitions. Three-dimensional FOM did not show significant interuser variability, whereas 2D PISA did.

CONCLUSIONS

Three-dimensional FOM may provide increased clinical value compared with 2D PISA because of increased accuracy in the case of complex or severe regurgitant orifices as well as its greater repeatability and simpler work flow.

How Local Annular Force and Collagen Density Govern Mitral Annuloplasty Ring Dehiscence Risk

BACKGROUND

Annuloplasty ring dehiscence is a well described mode of mitral valve repair failure. Defining the mechanisms underlying dehiscence may facilitate its prevention.

METHODS

Factors that govern suture dehiscence were examined with an ovine model. After undersized ring annuloplasty in live animals (n = 5), cyclic force (FC) that acts on sutures during cardiac contraction was measured with custom transducers. FC was measured at ten suture positions, throughout cardiac cycles with peak left ventricular pressure (LVPmax) of 100, 125, and 150 mm Hg. Suture pullout testing was conducted on explanted mitral annuli (n = 12) to determine suture holding strength at each position. Finally, relative collagen density differences at suture sites around the annulus were assessed by two-photon excitation fluoroscopy.

RESULTS

Anterior FC exceeded posterior FC at each LVPmax (eg, 2.8 ± 1.3 N versus 1.8 ± 1.2 N at LVPmax = 125 mm Hg, p < 0.01). Anterior holding strength exceeded posterior holding strength (6.4 ± 3.6 N versus 3.9 ± 1.6 N, p < 0.0001). On the basis of FC at LVPmax of 150 mm Hg, margin of safety before suture pullout was vastly higher between the trigones (exclusive) versus elsewhere (4.8 ± 0.9 N versus 1.9 ± 0.5 N, p < 0.001). Margin of safety exhibited strong correlation to collagen density (R(2) = 0.947).

CONCLUSIONS

Despite lower cyclic loading on posterior sutures, the weaker posterior mitral annular tissue creates higher risk of dehiscence, apparently because of reduced collagen content. Sutures placed atop the trigones are less secure than predicted, because of a combination of reduced collagen and higher overall rigidity in this region. These findings highlight the inter-trigonal tissue as the superior anchor and have implications on the design and implantation techniques for next-generation mitral prostheses.

Bench Models for Assessing the Mechanics of Mitral Valve Repair and Percutaneous Surgery

Rapid preclinical evaluations of mitral valve (MV) mechanics are currently best facilitated by bench models of the left ventricle (LV). This review aims to provide a comprehensive assessment of these models to aid interpretation of their resulting data, inform future experimental evaluations, and further the translation of results to procedure and device development. For this review, two types of experimental bench models were evaluated. Rigid LV models were characterized as fluid-mechanical systems capable of testing explanted MVs under static and or pulsatile left heart hemodynamics. Passive LV models were characterized as explanted hearts whose left side is placed in series with a static or pulsatile flow-loop. In both systems, MV function and mechanics can be quantitatively evaluated. Rigid and passive LV models were characterized and evaluated. The materials and methods involved in their construction, function, quantitative capabilities, and disease modeling were described. The advantages and disadvantages of each model are compared to aid the interpretation of their resulting data and inform future experimental evaluations. Repair and percutaneous studies completed in these models were additionally summarized with perspective on future advances discussed. Bench models of the LV provide excellent platforms for quantifying MV repair mechanics and function. While exceptional work has been reported, more research and development is necessary to improve techniques and devices for repair and percutaneous surgery. Continuing efforts in this field will significantly contribute to the further development of procedures and devices, predictions of long-term performance, and patient safety.

Novel Method to Track Soft Tissue Deformation by Micro-Computed Tomography: Application to the Mitral Valve

Increasing availability of micro-computed tomography (µCT) as a structural imaging gold-standard is bringing unprecedented geometric detail to soft tissue modeling. However, the utility of these advances is severely hindered without analogous enhancement to the associated kinematic detail. To this end, labeling and following discrete points on a tissue across various deformation states is a well-established approach. Still, existing techniques suffer limitations when applied to complex geometries and large deformations and strains. Therefore, we herein developed a non-destructive system for applying fiducial markers (minimum diameter: 500 µm) to soft tissue and tracking them through multiple loading conditions by µCT. Using a novel applicator to minimize adhesive usage, four distinct marker materials were resolvable from both tissue and one another, without image artifacts. No impact on tissue stiffness was observed. µCT addressed accuracy limitations of stereophotogrammetry (inter-method positional error 1.2 ± 0.3 mm, given marker diameter 1.9 ± 0.1 mm). Marker application to ovine mitral valves revealed leaflet Almansi areal strains (45 ± 4%) closely matching literature values, and provided radiographic access to previously inaccessible regions, such as the leaflet coaptation zone. This system may meaningfully support mechanical characterization of numerous tissues or biomaterials, as well as tissue-device interaction studies for regulatory standards purposes.

Mitral valve annuloplasty and anterior leaflet augmentation for functional ischemic mitral regurgitation: quantitative comparison of coaptation and subvalvular tethering

OBJECTIVE

Although restrictive mitral annuloplasty (RMA) has been the preferred surgical treatment of functional ischemic mitral regurgitation (FIMR), some patients with severely dilated left ventricles will experience recurrent mitral regurgitation (MR). Consequently, new surgical strategies have been entertained to compensate for severely dilated ventricles by maximizing coaptation and reducing subvalvular tethering. Anterior leaflet augmentation (ALA) with mitral annuloplasty has been theorized to meet these goals. We compared the mechanistic effects of RMA and adjunct ALA in the setting of FIMR.

METHODS

Mitral valves were mounted in a clinically relevant left heart simulator. The tested conditions included control, FIMR, RMA, and true-size annuloplasty with either a small or large ALA. The A2-P2 leaflet coaptation length, MR, and strut and intermediary chordal forces were quantified. All repairs alleviated the MR. The coaptation length was significantly increased from FIMR to RMA, small ALA, and large ALA (P<.001). Between repairs, a large ALA created the greatest length of coaptation (P<.05). Tethering forces from the posteromedial strut chordae were reduced from the FIMR condition by all repairs (P<.001). Only a large ALA reduced the intermediate chordal tethering from the FIMR condition (P<.05).

CONCLUSIONS

A large ALA procedure created the greatest coaptation and reduced chordal tethering. Although all repairs abolished MR acutely, the repairs that create the greatest coaptation might conceivably produce a more robust and lasting repair in the chronic stage. A clinical need still exists to best identify which patients with altered mitral valve geometries would most benefit from an adjunct procedure or RMA alone.

Quantitative Evaluation of Annuloplasty on Mitral Valve Chordae Tendineae Forces to Supplement Surgical Planning Model Development

PURPOSE

Computational models of the heart's mitral valve (MV) exhibit potential for preoperative surgical planning in ischemic mitral regurgitation (IMR). However challenges exist in defining boundary conditions to accurately model the function and response of the chordae tendineae to both IMR and surgical annuloplasty repair. Towards this goal, a ground-truth data set was generated by quantifying the isolated effects of IMR and mitral annuloplasty on leaflet coaptation, regurgitation, and tethering forces of the anterior strut and posterior intermediary chordae tendineae.

METHODS

MVs were excised from ovine hearts (N=15) and mounted in a pulsatile heart simulator which has been demonstrated to mimic the systolic MV geometry and coaptation of healthy and chronic IMR sheep. Strut and intermediary chordae from both MV leaflets (N=4) were instrumented with force transducers. Tested conditions included a healthy control, IMR, oversized annuloplasty, true-sized annuloplasty, and undersized mitral annuloplasty. A2-P2 leaflet coaptation length, regurgitation, and chordal tethering were quantified and statistically compared across experimental conditions.

RESULTS

IMR was successfully simulated with significant increases in MR, tethering forces for each of the chordae, and decrease in leaflet coaptation (p<.05). Compared to the IMR condition, increasing levels of downsized annuloplasty significantly reduced regurgitation, increased coaptation, reduced posteromedial papillary muscle strut chordal forces, and reduced intermediary chordal forces from the anterolateral papillary muscle (p<.05).

CONCLUSIONS

These results provide for the first time a novel comprehensive data set for refining the ability of computational MV models to simulate IMR and varying sizes of complete rigid ring annuloplasty.

Isolated effect of geometry on mitral valve function for in silico model development

Computational models for the heart's mitral valve (MV) exhibit several uncertainties that may be reduced by further developing these models using ground-truth data-sets. This study generated a ground-truth data-set by quantifying the effects of isolated mitral annular flattening, symmetric annular dilatation, symmetric papillary muscle (PM) displacement and asymmetric PM displacement on leaflet coaptation, mitral regurgitation (MR) and anterior leaflet strain. MVs were mounted in an in vitro left heart simulator and tested under pulsatile haemodynamics. Mitral leaflet coaptation length, coaptation depth, tenting area, MR volume, MR jet direction and anterior leaflet strain in the radial and circumferential directions were successfully quantified at increasing levels of geometric distortion. From these data, increase in the levels of isolated PM displacement resulted in the greatest mean change in coaptation depth (70% increase), tenting area (150% increase) and radial leaflet strain (37% increase) while annular dilatation resulted in the largest mean change in coaptation length (50% decrease) and regurgitation volume (134% increase). Regurgitant jets were centrally located for symmetric annular dilatation and symmetric PM displacement. Asymmetric PM displacement resulted in asymmetrically directed jets. Peak changes in anterior leaflet strain in the circumferential direction were smaller and exhibited non-significant differences across the tested conditions. When used together, this ground-truth data-set may be used to parametrically evaluate and develop modelling assumptions for both the MV leaflets and subvalvular apparatus. This novel data may improve MV computational models and provide a platform for the development of future surgical planning tools.

Epicardial catheter-based ventricular reconstruction: a novel therapy for ischaemic heart failure with anteroapical aneurysm

OBJECTIVES

Surgical ventricular reconstruction has been used to treat ischaemic cardiomyopathy with large akinetic or dyskinetic areas. However, application of this approach requires a sternotomy, cardiopulmonary bypass and a left ventriculotomy. This study assessed the feasibility and efficacy of minimally invasive, off-pump, epicardial catheter-based ventricular reconstruction (ECVR) in an anteroapical aneurysm ovine model.

METHODS

Left ventricular (LV) anteroapical myocardial infarction was induced percutaneously by coil embolization of the left anterior descending coronary artery. Eight weeks after infarction, via mini left thoracotomy and without cardiopulmonary bypass, ECVR was performed in six sheep. The scar was excluded by placing anchor pairs on the LV epicardial anterior wall and the right ventricular side of the interventricular septum under fluoroscopic guidance. LV performance was evaluated before, immediately after device implantation and after 6 weeks by echocardiography. Terminal histopathology was performed.

RESULTS

ECVR was completed expeditiously in all animals without complications. Parameters obtained 6 weeks after device implantation were compared with baseline (pre-device). End-systolic volume was decreased by 38% (25.6 ± 6.1 ml vs baseline 41.2 ± 7.2 ml, P = 0.02) with preservation of stroke volume. Ejection fraction was significantly increased by 13% (48.5 ± 7% vs baseline 35.8 ± 7%, P = 0.02). The circumferential strain in the anterior septum (-7.67 ± 5.12% vs baseline -0.96 ± 2.22%, P = 0.03) and anterior wall (-9.01 ± 3.51% vs baseline -4.15 ± 1.36%, P = 0.01) were significantly improved. The longitudinal strain in apex was reversed (-3.08 ± 1.53% vs baseline 3.09 ± 3.39%, P = 0.01). Histopathology showed full endocardial healing over the anchors with appreciable reduction of the chronic infarct in the LV.

CONCLUSIONS

ECVR without cardiopulmonary bypass is a less invasive alternative to current standard therapies, reverses LV remodelling and improves cardiac performance in an ovine model of anteroapical aneurysm.

Accuracy of a mitral valve segmentation method using J-splines for real-time 3D echocardiography data

Patient-specific models of the heart's mitral valve (MV) exhibit potential for surgical planning. While advances in 3D echocardiography (3DE) have provided adequate resolution to extract MV leaflet geometry, no study has quantitatively assessed the accuracy of their modeled leaflets vs. a ground-truth standard for temporal frames beyond systolic closure or for differing valvular dysfunctions. The accuracy of a 3DE-based segmentation methodology based on J-splines was assessed for porcine MVs with known 4D leaflet coordinates within a pulsatile simulator during closure, peak closure, and opening for a control, prolapsed, and billowing MV model. For all time points, the mean distance error between the segmented models and ground-truth data were 0.40 ± 0.32 mm, 0.52 ± 0.51 mm, and 0.74 ± 0.69 mm for the control, flail, and billowing models. For all models and temporal frames, 95% of the distance errors were below 1.64 mm. When applied to a patient data set, segmentation was able to confirm a regurgitant orifice and post-operative improvements in coaptation. This study provides an experimental platform for assessing the accuracy of an MV segmentation methodology at phases beyond systolic closure and for differing MV dysfunctions. Results demonstrate the accuracy of a MV segmentation methodology for the development of future surgical planning tools.