Patient-specific Mitral Valve Research Articles

Replicated mitral valve models from real patients offer training opportunities for minimally invasive mitral valve repair

Minimally invasive mitral valve repair is considered a challenging procedure. Mastering the necessary skills takes years of training and clinical experience. To date, reconstructive surgery is performed mainly by a few surgeons with a strong track record, whereas trainees have only limited opportunities to practise. A high-fidelity training simulator was equipped with novel silicone replicas of patient-specific mitral valves containing all of the anatomical components of the valve. The goal of this system was to aid members of the surgical community to overcome the steep learning curve. Twelve surgeons (5 experts and 7 surgical resident trainees) performed a minimally invasive mitral valve repair procedure on these models and assessed the usefulness for different applications. The trainees found the main application to be general surgical training and education for mitral valve repair, whereas the experts found the main benefit to be rehearsal for a specific patient. The skills of the trainees were improved in only a single session. The valve models placed in a water solution showed a high echogenicity. Preoperative patient-specific simulation could improve the safety and effectiveness of mitral valve repair in the hands of a larger number of surgeons. Because the system is based on a quantitative segmentation of the anatomy of the mitral valve, it offers young surgeons training in general dexterity and also provides an exact numerical quantitative assessment of valvular geometry. This system can be used to educate surgeons to strive for and achieve well-defined and measurable surgical changes to the anatomy of the valve and to achieve the desired functional results.

Temporal Views of Flattened Mitral Valve Geometries.

The mitral valve, one of the four valves in the human heart, controls the bloodflow between the left atrium and ventricle and may suffer from various pathologies. Malfunctioning valves can be treated by reconstructive surgeries, which have to be carefully planned and evaluated. While current research focuses on the modeling and segmentation of the valve, we base our work on existing segmentations of patient-specific mitral valves, that are also time-resolved ( 3D+t) over the cardiac cycle. The interpretation of the data can be ambiguous, due to the complex surface of the valve and multiple time steps. We therefore propose a software prototype to analyze such 3D+t data, by extracting pathophysiological parameters and presenting them via dimensionally reduced visualizations. For this, we rely on an existing algorithm to unroll the convoluted valve surface towards a flattened 2D representation. In this paper, we show that the 3D+t data can be transferred to 3D or 2D representations in a way that allows the domain expert to faithfully grasp important aspects of the cardiac cycle. In this course, we not only consider common pathophysiological parameters, but also introduce new observations that are derived from landmarks within the segmentation model. Our analysis techniques were developed in collaboration with domain experts and a survey showed that the insights have the potential to support mitral valve diagnosis and the comparison of the pre- and post-operative condition of a patient.

Abstract 17214: Prediction of Mitral Valve Repair: Pre-Repair versus Virtual Repair versus Post-Repair

Introduction: Partial leaflet resection followed by ring annuloplasty is a reliable and reproducible mitral valve (MV) repair technique for the treatment of severe mitral regurgitation (MR) due to posterior chordal rupture. Hypothesis: We have developed a novel computational virtual MV repair strategy to predict the biomechanical and physiologic characteristics of post-repair MV dynamics to help with optimal surgical planning. Methods: Computational MV models were created using pre- and post-repair 3D echocardiographic data of a patient having posterior chordal rupture and severe MR. Virtual resection was designed by removing a pre-defined triangle-shaped leaflet portion in the P2 scallop and merging the excised leaflet edges. Virtual ring annuloplasty with the same ring size as the post-repair MV was performed following the triangular leaflet resection. Computational simulations of MV function (pre-repair, virtual repair, and post-repair) were performed using dynamic finite element methods. Leaflet coaptation across the MVs were quantitatively determined and compared. Results: The pre-repair MV with P2 chordal rupture showed severe P2 prolapse and leaflet malcoaptation. The post-repair MV demonstrated markedly reduced prolapse and sufficiently restored leaflet coaptation. The virtually repaired MV revealed a similar coaptation ratio as the post-repair MV indicating effective restoration of normal MV function. Both virtual repair and post-repair MVs showed improved coaptation not only in the P2 region but also in the A1-P1 and A3-P3 regions. Conclusions: We have quantitatively evaluated patient-specific MV function before and after potential MV repair using a novel virtual MV repair protocol. Both virtual repair and post-repair MVs decreased posterior leaflet prolapse and restored normal coaptation. This virtual MV repair strategy has the potential for improved pre-surgical planning to predict and optimize post-repair MV function.

Feasibility of Ultrasound-Based Computational Fluid Dynamics as a Mitral Valve Regurgitation Quantification Technique: Comparison with 2-D and 3-D Proximal Isovelocity Surface Area-Based Methods

Current Doppler echocardiography quantification of mitral regurgitation (MR) severity has shortcomings. Proximal isovelocity surface area (PISA)-based methods, for example, are unable to account for the fact that ultrasound Doppler can measure only one velocity component: toward or away from the transducer. In the present study, we used ultrasound-based computational fluid dynamics (Ub-CFD) to quantify mitral regurgitation and study its advantages and disadvantages compared with 2-D and 3-D PISA methods. For Ub-CFD, patient-specific mitral valve geometry and velocity data were obtained from clinical ultrasound followed by 3-D CFD simulations at an assumed flow rate. We then obtained the average ratio of the ultrasound Doppler velocities to CFD velocities in the flow convergence region, and scaled CFD flow rate with this ratio as the final measured flow rate. We evaluated Ub-CFD, 2-D PISA and 3-D PISA with an in vitro flow loop, which featured regurgitation flow through (i) a simplified flat plate with round orifice and (ii) a 3-D printed realistic mitral valve and regurgitation orifice. The Ub-CFD and 3-D PISA methods had higher precision than the 2-D PISA method. Ub-CFD had consistent accuracy under all conditions tested, whereas 2-D PISA had the lowest overall accuracy. In vitro investigations indicated that the accuracy of 2-D and 3-D PISA depended significantly on the choice of aliasing velocity. Evaluation of these techniques was also performed for two clinical cases, and the dependency of PISA on aliasing velocity was similarly observed. Ub-CFD was robustly accurate and precise and has promise for future translation to clinical practice.

Computational virtual evaluation of the effect of annuloplasty ring shape.

Mitral regurgitation (MR) is a result of mitral valve (MV) pathology. Its etiology can be categorized as degenerative or functional MR. Ring annuloplasty aims to reconfigure a dilated mitral annulus to its normal size and shape. We investigated the effect of annuloplasty ring shape on MR outcome using our established 3-dimensional (3-D) echocardiography-based computational MV evaluation protocols. Virtual patient MV models were created from 3-D transesophageal echocardiographic data in patients with MR because of mitral annular dilation. Two distinct annuloplasty rings (Physio II and GeoForm) were designed and virtually implanted to the patient MVs. Dynamic finite element simulations of MV function were performed for each MV after virtual ring annuloplasty of either ring, and physiologic and biomechanical characteristics of MV function were compared. Excessive stress values appeared primarily in the midanterior and midposterior regions, and lack of leaflet coaptation was found in pre-annuloplasty patient MVs. Both rings demonstrated marked reduction of stresses and efficient leaflet coaptation. The Physio II ring demonstrated more evenly distributed stress reduction across the leaflets and annulus compared with the GeoForm ring. Conversely, the highly nonplanar curvature of the GeoForm ring more effectively increased leaflet coaptation compared with the Physio II ring. This indicates that the shape of annuloplasty ring affects post-annuloplasty physiologic and biomechanical conditions, which can lead to tissue alteration over a longer period after ring annuloplasty. This virtual ring annuloplasty simulation strategy provides detailed physiologic and biomechanical information and may help better plan the optimal ring selection and improved patient-specific MV repairs.

Towards patient-specific modeling of mitral valve repair: 3D transesophageal echocardiography-derived parameter estimation.

Transesophageal echocardiography (TEE) is routinely used to provide important qualitative and quantitative information regarding mitral regurgitation. Contemporary planning of surgical mitral valve repair, however, still relies heavily upon subjective predictions based on experience and intuition. While patient-specific mitral valve modeling holds promise, its effectiveness is limited by assumptions that must be made about constitutive material properties. In this paper, we propose and develop a semi-automated framework that combines machine learning image analysis with geometrical and biomechanical models to build a patient-specific mitral valve representation that incorporates image-derived material properties. We use our computational framework, along with 3D TEE images of the open and closed mitral valve, to estimate values for chordae rest lengths and leaflet material properties. These parameters are initialized using generic values and optimized to match the visualized deformation of mitral valve geometry between the open and closed states. Optimization is achieved by minimizing the summed Euclidean distances between the estimated and image-derived closed mitral valve geometry. The spatially varying material parameters of the mitral leaflets are estimated using an extended Kalman filter to take advantage of the temporal information available from TEE. This semi-automated and patient-specific modeling framework was tested on 15 TEE image acquisitions from 14 patients. Simulated mitral valve closures yielded average errors (measured by point-to-point Euclidean distances) of 1.86 ± 1.24mm. The estimated material parameters suggest that the anterior leaflet is stiffer than the posterior leaflet and that these properties vary between individuals, consistent with experimental observations described in the literature.

3D Printed Modeling of the Mitral Valve for Catheter-Based Structural Interventions.

As catheter-based structural heart interventions become increasingly complex, the ability to effectively model patient-specific valve geometry as well as the potential interaction of an implanted device within that geometry will become increasingly important. Our aim with this investigation was to combine the technologies of high-spatial resolution cardiac imaging, image processing software, and fused multi-material 3D printing, to demonstrate that patient-specific models of the mitral valve apparatus could be created to facilitate functional evaluation of novel trans-catheter mitral valve repair strategies. Clinical 3D transesophageal echocardiography and computed tomography images were acquired for three patients being evaluated for a catheter-based mitral valve repair. Target anatomies were identified, segmented and reconstructed into 3D patient-specific digital models. For each patient, the mitral valve apparatus was digitally reconstructed from a single or fused imaging data set. Using multi-material 3D printing methods, patient-specific anatomic replicas of the mitral valve were created. 3D print materials were selected based on the mechanical testing of elastomeric TangoPlus materials (Stratasys, Eden Prairie, Minnesota, USA) and were compared to freshly harvested porcine leaflet tissue. The effective bending modulus of healthy porcine MV tissue was significantly less than the bending modulus of TangoPlus (p<0.01). All TangoPlus varieties were less stiff than the maximum tensile elastic modulus of mitral valve tissue (3697.2 ± 385.8kPa anterior leaflet; 2582.1 ± 374.2kPa posterior leaflet) (p<0.01). However, the slopes of the stress-strain toe regions of the mitral valve tissues (532.8 ± 281.9kPa anterior leaflet; 389.0 ± 156.9kPa posterior leaflet) were not different than those of the Shore 27, Shore 35, and Shore 27 with Shore 35 blend TangoPlus material (p>0.95). We have demonstrated that patient-specific mitral valve models can be reconstructed from multi-modality imaging datasets and fabricated using the multi-material 3D printing technology and we provide two examples to show how catheter-based repair devices could be evaluated within specific patient 3D printed valve geometry. However, we recognize that the use of 3D printed models for the development of new therapies, or for specific procedural training has yet to be defined.

3D Printed Modeling for Patient-Specific Mitral Valve Intervention: Repair With a Clip and a Plug.

A 62-year-old man with peripheral vascular disease, chronic kidney disease (glomerular filtration rate <30 ml/min), previous coronary artery bypass grafting, and recent treatment for bacterial endocarditis was referred for refractory decompensated congestive heart failure (New York Heart

Hemodynamic Testing of Patient-Specific Mitral Valves Using a Pulse Duplicator: A Clinical Application of Three-Dimensional Printing.

To evaluate the feasibility of obtaining hemodynamic metrics of echocardiographically derived 3-dimensional printed mitral valve models deployed in a pulse-duplicator chamber. Exploratory study. Tertiary-care university hospital. Percutaneous MitraClip procedure patient. Three-dimensional R-wave gated, full-volume transesophageal echocardiography images were obtained after deployment of the MitraClip device. A high-quality diastolic frame of the mitral valve was segmented using Mimics Innovation Suite and merged with a flange. The data were exported as a stereolithography (.stl) file, and a rigid 3-dimensional model was printed using a MakerBot Replicator 2 printer. A flexible silicone cast then was created and deployed in the pulse-duplicator chamber filled with a blood-mimicking fluid. The authors were able to obtain continuous-wave Doppler tracings of the valve inflow with a transesophageal echocardiography transducer. They also were able to generate diastolic ventricular and atrial pressure tracings. Pressure half-time and mitral valve area were computed from these measurements. This pulse duplicator shows promising applications in hemodynamic testing of patient-specific anatomy. Future modifications to the system may allow for visualization and data collection of gradients across the aortic valve.

Abstract 18319: Virtual Mitral Valve Repair for Improved Pre-surgical Planning: Quantitative Evaluation of Neochordoplasty versus Leaflet Resection

Background: Neochordoplasty and/or leaflet resection are reliable and reproducible mitral valve (MV) repair techniques for the treatment of chordal rupture with severe mitral regurgitation (MR). We developed a novel computational evaluation strategy to determine the biomechanical and physiologic characteristics of MV dynamics prior to and following potential MV repair techniques to optimize surgical planning for neochordoplasty or leaflet resection. Methods: Virtual MV models from patients with P2 chordal rupture and severe MR were created using 3D echocardiographic data (N=5). Virtual neochordoplasty was designed by adding six neochordae between the papillary muscles and the P2 scallop. Virtual resection was performed by removing a pre-defined quadrangular shaped leaflet portion in the P2 scallop and merging the excised leaflet edges. Computational simulations of MV function (pre- and post-repair) were performed using dynamic finite element methods. Coaptation lengths and leaflet stress distributions were evaluated. Results: The MVs with P2 chordal rupture demonstrated severe P2 prolapse, leaflet malcoaptation, and large stress concentrations. Both repair techniques markedly reduced posterior leaflet prolapse and restored sufficient leaflet coaptation. Virtual neochordoplasty showed larger coaptation lengths (A2-P2) compared to virtual resection. Excessive stress concentrations in the P2 scallop disappeared and peak stress values decreased by up to 85% following both repair techniques. Conclusion: We have quantitatively evaluated patient-specific MV function before and after potential MV repair using a novel virtual MV repair protocol. Both virtual neochordoplasty and leaflet resection techniques decreased posterior leaflet prolapse, lessened stress concentration, and restored leaflet coaptation. This virtual simulation strategy has the potential for improved pre-surgical planning to optimize post-repair MV function.

Mass-spring systems for simulating mitral valve repair using 3D ultrasound images

Mitral valve (MV) diseases are among the most common types of heart diseases, while heart diseases are the most common cause of death worldwide. MV repair surgery is connected to higher survival rates and fewer complications than the total replacement of the MV, but MV repair requires extensive patient-specific therapy planning. The simulation of MV repair with a patient-specific model could help to optimize surgery results and make MV repair available to more patients. However, current patient-specific simulations are difficult to transfer to clinical application because of time-constraints or prohibitive requirements on the resolution of the image data. As one possible solution to the problem of patient-specific MV modeling, we present a mass-spring MV model based on 3D transesophageal echocardiographic (TEE) images already routinely acquired for MV repair therapy planning. Our novel approach to the rest-length estimation of springs allows us to model the global support of the MV leaflets through the chordae tendinae without the need for high-resolution image data. The model is used to simulate MV annuloplasty for five patients undergoing MV repair, and the simulated results are compared to post-surgical TEE images. The comparison shows that our model is able to provide a qualitative estimate of annuloplasty surgery. In addition, the data suggests that the model might also be applied to simulating the implantation of artificial chordae.

Abstract 15648: Quantitative Evaluation of Mitral Valve Dynamics for Improved Planning of Mitral Valve Repairs

Introduction: Mitral valve (MV) repair with ring annuloplasty is the standard surgical technique for the treatment of mitral regurgitation (MR). Long-term studies report MR recurrence in up to 2-4% of repairs. We have developed a novel computational evaluation strategy to determine the biomechanical and physiologic characteristics of MV dynamics prior to and following virtual MV repair to help with optimal surgical planning. Methods: Virtual MV models from patients with large annular dilation and severe MR in the anterolateral region were created using 3D echocardiographic data sets. Two different types of annuloplasty rings were modeled in the simulation: Physio (flat) and Physio II (saddle-shaped). Proper ring size was determined using standard clinical guidelines. Computational simulations of MV function (pre- and post-repair) were performed using dynamic finite element methods. Coaptation ratio (CR) and structural stress distribution across the MVs were determined and compared. Results: Pathologic MVs demonstrated substantial anterolateral malcoaptation (CR=0.34, Fig. 1A). Following virtual ring annuloplasty, there was marked improvement in coaptation (CR=0.65 for Physio, CR=0.62 for Physio II). Pre-repair simulation revealed large stress concentrations over the posterior leaflet (Fig. 1B). Stress concentration decreased by 54% after virtual MV repair. The saddle-shaped Physio II ring demonstrated more evenly distributed stress reduction while the flat ring (Physio) more effectively increased leaflet coaptation. Conclusion: We have quantitatively evaluated patient-specific MV function before and after MV repair using a novel computational simulation protocol. Virtual ring annuloplasty simulation demonstrated sufficient restoration of leaflet coaptation and reduced stress concentration following repair. This simulation strategy has the potential for improved pre-surgical planning and intraoperative evaluation of MV repair.

A novel finite element-based patient-specific mitral valve repair: virtual ring annuloplasty

Alterations of normal mitral valve (MV) function lead to mitral insufficiency, i.e., mitral regurgitation (MR). Mitral repair is the most popular and most efficient surgical intervention for MR treatment. An annuloplasty ring is implanted following complex reconstructive MV repairs to prevent potential reoccurrence of MR. We have developed a novel finite element (FE)-based simulation protocol to perform patient-specific virtual ring annuloplasty following the standard clinical guideline procedure. A virtual MV was created using 3D echocardiographic data in a patient with mitral annular dilation. Proper type and size of the ring were determined in consideration of the MV apparatus geometry. The ring was positioned over the patient MV model and annuloplasty was simulated. Dynamic simulation of MV function across the complete cardiac cycle was performed. Virtual patient-specific annuloplasty simulation well demonstrated morphologic information of the MV apparatus before and after ring implantation. Dynamic simulation of MV function following ring annuloplasty demonstrated markedly reduced stress distribution across the MV leaflets and annulus as well as restored leaflet coaptation compared to pre-annuloplasty. This novel FE-based patient-specific MV repair simulation technique provides quantitative information of functional improvement following ring annuloplasty. Virtual MV repair strategy may effectively evaluate and predict interventional treatment for MV pathology.

The effect of patient-specific annular motion on dynamic simulation of mitral valve function

Most surgical procedures for patients with mitral regurgitation (MR) focus on optimization of annular dimension and shape utilizing ring annuloplasty to restore normal annular geometry, increase leaflet coaptation, and reduce regurgitation. Computational studies may provide insight on the effect of annular motion on mitral valve (MV) function through the incorporation of patient-specific MV apparatus geometry from clinical imaging modalities such as echocardiography. In the present study, we have developed a novel algorithm for modeling patient-specific annular motion across the cardiac cycle to further improve our virtual MV modeling and simulation strategy. The MV apparatus including the leaflets, annulus, and location of papillary muscle tips was identified using patient 3D echocardiography data at end diastole and peak systole and converted to virtual MV model. Dynamic annular motion was modeled by incorporating the ECG-gated time-varying scaled annular displacement across the cardiac cycle. We performed dynamic finite element (FE) simulation of two sets of patient data with respect to the presence of MR. Annular morphology, stress distribution across the leaflets and annulus, and contact stress distribution were determined to assess the effect of annular motion on MV function and leaflet coaptation. The effect of dynamic annular motion clearly demonstrated reduced regions with large stress values and provided an improved accuracy in determining the location of improper leaflet coaptation. This strategy has the potential to better quantitate the extent of pathologic MV and better evaluate functional restoration following MV repair.

Mitral Valve Patient-Specific Finite Element Modeling from Cardiac MRI: Application to an Annuloplasty Procedure

We aim at testing the possibility to build patient-specific structural finite element models (FEMs) of the mitral valve (MV) from cardiac magnetic resonance (CMR) imaging and to use them to predict the outcome of mitral annuloplasty procedures. MV FEMs were built for one healthy subject and for one patient with ischemic mitral regurgitation. On both subjects, CMR imaging of 18 long-axis planes was performed with a temporal resolution of 55 time-frames per cardiac cycle. Three-dimensional MV annulus geometry, leaflets surface and PM position were manually obtained using custom software. Hyperelastic anisotropic mechanical properties were assigned to MV tissues. A physiological pressure load was applied to the leaflets to simulate valve closure until peak systole. For the pathological model only, a further simulation was run, simulating undersized rigid annuloplasty before valve closure. Closure dynamics, leaflets stresses and tensions in the subvalvular apparatus in the healthy MV were consistent with previous computational and experimental data. The regurgitant valve model captured with good approximation the real size and position of regurgitant areas at peak systole, and highlighted abnormal tensions in the annular region and sub-valvular apparatus. The simulation of undersized rigid annuloplasty showed the restoration of MV continence and normal tensions in the subvalvular apparatus and at the annulus. Our method seems suitable for implementing detailed patient-specific MV FEMs to simulate different scenarios of clinical interest. Further work is mandatory to test the method more deeply, to reduce its computational time and to expand the range of modeled surgical procedures.