Transcatheter mitral valve replacement (TMVR) is an emerging therapy for patients with severe mitral valve disease considered unsuitable for conventional surgery. Pre-procedural planning is paramount to avoiding left ventricular outflow tract (LVOT) obstruction, a prevalent and potentially lethal complication of TMVR. The current method to predict LVOT obstruction involves estimating the cross-sectional area of the elongated LVOT after TMVR (i.e. neo-LVOT) using computed tomography (CT) by overlaying a virtual device onto the anatomy in a single phase of the cardiac cycle.

In the interventional treatment of tricuspid valve regurgitation, the majority of prosthetic devices interact with or are implanted to the tricuspid valve annulus. For new transcatheter technologies, there exists a growing body of clinical experience, literature, and professional discourse related to the difficulties in delivering, securing, and sustaining the function of these devices within the dynamic tricuspid annulus. Many of the difficulties arise from circumstances not encountered in open-heart surgery, namely; a non-arrested heart, indirect visualization, and a reliance on non-suture-based methods. These challenges require the application of procedural techniques or system designs to account for tricuspid annular motion, forces, and underlying tissue strength. Improved knowledge in these interactions will support the goals of improving device systems, their procedures, and patient outcomes. This review aims to describe current concepts of tricuspid annular mechanics, key device and procedural implications, and highlight current knowledge gaps for future consideration.

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

Objective: The study objective was to develop a novel annuloplasty ring with regional flexibility and assess its suture force dynamics in healthy ovine subjects compared with fully rigid or fully flexible rings. Methods: Materially heterogeneous rings were created with rigid anterior and posterior, and flexible commissural segments. These rings were created to match the geometry of the Profile 3D ring (Medtronic, Minneapolis, Minn). Each ring was instrumented with 10 force transducers to measure cyclic suture forces (FC) and undersized annuloplasty was performed in 6 healthy ovine subjects. Each FC was recorded and examined for cardiac cycles reaching a maximum left ventricular pressure of 100, 125, and 150 mm Hg. FC was compared with previously reported values from fully rigid Profile 3D and fully flexible prototype rings. Results: Relative to the fully rigid ring, the heterogeneous ring exhibited 48% reduction in FC at its commissural (rigid vs heterogeneous: 1.80 +/- 0.94 N vs 0.95 +/- 0.52 N; P<.001) and 32% reduction in posterior (1.90 +/- 0.92 N vs 1.29 +/- 0.91 N; P<.001) regions, but not in its anterior region (2.45 +/- 1.21 N vs 2.23 +/- 1.22 N; P = .279). Relative to the fully flexible ring, the heterogeneous ring exhibited no significant differences in FC in any region. Conclusions: The reduced FC of the heterogeneous ring relative to the fully rigid ring suggests a promising approach to reduce suture loading while preserving the annular remodeling capability of fully rigid rings. Future studies in diseased subjects are necessary to explore repair effectiveness of this ring.

Transcatheter mitral valve (TMV) replacement technology has great clinical potential for surgically inoperable patients suffering from mitral regurgitation. An important goal for robust TMV design is maximizing the likelihood of achieving a geometry post-implant that facilitates optimal performance. To support this goal, improved understanding of the annular forces that oppose TMV radial expansion is necessary. In Part II of this study, novel circular and D-shaped Radial Expansion Force Transducers (C-REFT and D-REFT) were developed and employed in porcine hearts (N = 12), to detect the forces required to radially expand the mitral annulus to discrete oversizing levels. Forces on both the septal-lateral and inter-commissural axes (FSL and FIC) scaled with device size. The D-REFT experienced lower FSL than the C-REFT (19.8 ± 7.4 vs. 17.4 ± 10.8 N, p = 0.002) and greater FIC (31.5 ± 14.0 vs. 36.9 ± 16.2 N; p = 0.002), and was more sensitive to degree of oversizing. Across all tests, FIC/FSL was 2.21 ± 1.33, likely reflecting low resistance to radial expansion at the aorto-mitral curtain. In conclusion, the annular forces opposing TMV radial expansion are non-uniform, and depend on final TMV shape and size. Based on this two-part study, we propose that radial force applied at the commissural aspect of the annulus has the most potent effect on paravalvular sealing.

Annuloplasty ring repair is a common procedure for the correction of mitral valve regurgitation. Commercially available rings vary in dimensions and material properties. Annuloplasty ring suture dehiscence from the native annulus is a catastrophic yet poorly understood phenomenon that has been reported across ring types. Recognizing that sutures typically dehisce from the structurally weaker posterior annulus, our group is conducting a multi-part study in search of ring design parameters that influence forces acting on posterior annular sutures in the beating heart. Herein, we report the effect of ring rigidity on suture forces. Measurements utilized custom force sensors, attached to annuloplasty rings and implanted in normal ovine subjects via standard surgical procedure. Tested rings included the semi-rigid Physio (Edwards Lifesciences) and rigid and flexible prototypes of matching geometry. While no significant differences due to ring stiffness existed for sutures in the anterior region, posterior forces were significantly reduced with use of the flexible ring (rigid: 1.95 ± 0.96 N, semi-rigid: 1.76 ± 1.19 N, flexible: 1.04 ± 0.63 N; p < 0.001). The ratio of anterior to posterior FC scaled positively with increasing flexibility (p < 0.001), and posterior forces took more time to reach their peak load when a flexible ring was used (p < 0.001). This suggests a more rigid ring enables more rapid/complete force equilibration around the suture network, transferring higher anterior forces to the weaker posterior tissue. For mitral annuloplasties requiring ring rigidity, we propose a ring design concept to potentially disrupt this force transfer and improve suture retention.

Left ventricular outflow tract (LVOT) obstruction (LVOTO) is a potentially lethal complication that may arise in transcatheter mitral valve replacement (TMVR). Currently, a 2-dimensional (2-D) Neo-LVOT cross-sectional area of <189.4 mm2 is thought to increase the risk of LVOTO post-implantation.

Postoperative suture dehiscence is an important mode of short-term mitral and tricuspid valve (MV, TV) repair failure. We sought to evaluate suture pullout forces and collagen density in human atrioventricular valves for a better understanding of the comparative physiology between the valves and the underlying mechanobiological basis for suture retention. Mitral and tricuspid annuli were each excised from hearts from human donors age 60–79 with no history of heart disease ( n = 6). Anchor sutures were vertically pulled until tearing through the tissue. Suture pullout force ( F P ) was measured as the maximum force at dehiscence. Subsequently, tissue samples from each tested suture position were evaluated for collagen content using a standard hydroxyproline assay. Among all mitral positions, no significant differences were detected among positions or regions with mean F P values falling between 6.9 ± 2.6 N (posterior region) and 10.3 ± 4.7 N (anterior region). Among all tricuspid positions, the maximum F P and minimum F P were 24.0 ± 9.2 N (trigonal region) and 4.5 ± 2.6 N (anterior region). Although for the MV, a given sample’s collagen content had no correlation to its corresponding F P , the same relationship was significant for the TV. Further, the TV exhibited comparable F P to the MV overall, despite a nearly 40% reduction in collagen content. These findings suggest that sutures placed in the trigonal region of the TV have higher pullout force than those placed along other segments of the annuli. Furthermore, there are likely differences in collagen orientation between the mitral and tricuspid annuli, such that collagen content strongly impacts F P in one, but not the other.

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.

While transcatheter mitral valve (TMV) replacement technology has great clinical potential for surgically inoperable patients suffering from mitral regurgitation, no TMV has yet achieved regulatory approval. The diversity of devices currently under development reflects a lack of consensus regarding optimal design approaches. In Part I of this two-part study, a test system was developed for the quantification of paravalvular leakage (PVL) following deployment of a TMV or TMV-like device in pressurized, explanted porcine hearts ( N = 7). Using this system, PVL rate was investigated as a function of steady trans-mitral pressure (Δ P ), TMV shape, and TMV-annular oversizing, using a series of “mock TMV plug” devices. Across all devices, PVL was found to approximately trend with the square of Δ P . PVL rates were approximately 0–15 mL/s under hypotensive pressure, 10–40 mL/s under normotension, and 30–85 mL/s under severe hypertension. D-shaped devices significantly reduced PVL vs. circular devices; however, this effect was diminished upon oversizing to the annulus by 6 mm inter-trigonal distance. In conclusion, this steady pressure, in vitro test system was effective to compare PVL performance across TMV-like designs. PVL exhibited complex dynamics in terms of its response to transvalvular pressure and TMV profile.

Objective: The study objective was to quantify the effect of ring type, ring-annulus sizing, suture position, and surgeon on the forces required to tie down and constrain a mitral annuloplasty ring to a beating heart. Methods: Physio (Edwards Lifesciences, Irvine, Calif) or Profile 3D (Medtronic, Dublin, Ireland) annuloplasty rings were instrumented with suture force transducers and implanted in ovine subjects (N = 23). Tie-down forces and cyclic contractile forces were recorded and analyzed at 10 suture positions and at 3 levels of increasing peak left ventricular pressure. Results: Across all conditions, tie-down force was 2.7 +/- 1.4 N and cyclic contractile force was 2.0 +/- 1.2 N. Tie-down force was not meaningfully affected by any factor except surgeon. Significant differences in overall and individual tie-down forces were observed between the 2 primary implanting surgeons. No other factors were observed to significantly affect tie-down force. Contractile suture forces were significantly reduced by ring-annulus true sizing. This was driven almost exclusively by Physio cases and by reduction along the anterior aspect, where dehiscence is less common clinically. Contractile suture forces did not differ significantly between ring types. However, when undersizing, Profile 3D forces were significantly more uniform around the annular circumference. A suture's tie-down force did not correlate to its eventual contractile force. Conclusions: Mitral annuloplasty suture loading is influenced by ring type, ring-annulus sizing, suture position, and surgeon, suggesting that reports of dehiscence may not be merely a series of isolated errors. When compared with forces known to cause suture dehiscence, these in vivo suture loading data aid in establishing potential targets for reducing the occurrence of ring dehiscence.

Background. Surgical repair of functional tricuspid regurgitation (FTR) is an increasingly common practice, but annuloplasty suture dehiscence remains a significant problem. Quantitative and mechanistic understanding of annular suture holding strength can support more effective techniques for tricuspid valve device anchoring.Methods. Suture holding strength of ovine tricuspid annuli (n = 15) was quantified ex vivo by pullout testing at 12 positions around their circumference. Collagen density in additional annuli (n = 7) was quantified at positions above each commissure and midleaflet point by two-photon autofluorescence microscopy, enabling mechanistic assessment of its role in imparting suture holding strength to the tissue.Results. Suture holding strength from pullout testing varied significantly by annular position, with a maximum of 10.0 +/- 4.1 N at the septal leaflet (6 o'clock) and a minimum of 4.3 +/- 1.3 N at the posterior leaflet (1 o'clock). Leaflet midpoints showed significantly higher annular tissue strength than commissures (7.2 +/- 3.4 N versus 5.6 +/- 2.1 N, respectively, p = 0.008). Collagen density, measured by a normalized mean pixel intensity, was significantly higher in the septal annulus than in the posterior-septal commissure, posterior annulus, and anterior-posterior commissure. Suture holding strength showed a strong linear correlation with collagen density (R-2 = 0.822, p = 0.013).Conclusions. The clinical predominance of suture dehiscence at the septal annulus, despite its greater ex vivo holding strength, suggests either adverse suture placement techniques in this region or asymmetric tensile loading after implantation. This issue highlights the need to optimize implantation techniques and to carefully assess anchor security in existing and next-generation FTR corrective devices. (C) 2017 by The Society of Thoracic Surgeons

Central MessageDehiscence of a mitral annuloplasty ring suture redistributes tension to 2 adjacent sutures, creating a risk for further dehiscence.See Editorial Commentary page e19. Dehiscence of a mitral annuloplasty ring suture redistributes tension to 2 adjacent sutures, creating a risk for further dehiscence. See Editorial Commentary page e19. We present a case of annuloplasty suture dehiscence in a live ovine model, with novel, real-time suture force recordings throughout the event. Following repair of mitral regurgitation, annuloplasty ring suture dehiscence is a major cause of postoperative failure, accounting for approximately 19% of reoperations.1Gillinov A.M. Cosgrove D.M. Lytle B.W. Taylor P.C. Stewart R.W. McCarthy P.M. et al.Reoperation for failure of mitral valve repair.J Thorac Cardiovasc Surg. 1997; 113: 467-475Abstract Full Text Full Text PDF PubMed Scopus (138) Google Scholar Dehiscence may occur at 1 or multiple suture positions. We recently reported novel transducers capable of quantifying tension in individual sutures in the beating heart after mitral annuloplasty.2Siefert A.W. Pierce E.L. Lee M. Jensen M.Ø. Aoki C. Takebayashi S. et al.Suture forces in undersized mitral annuloplasty: novel device and measurements.Ann Thorac Surg. 2014; 98: 305-309Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar We have expanded these methods to evaluate the effects of ring size, shape, and ventricular function on suture forces, to identify physiological and device-specific factors that may affect suture dehiscence risk. As part of this study, a Profile3D ring (size, 26; Medtronic, Dublin, Ireland), instrumented with transducers, was implanted in a healthy 45-kg subject (annulus size, 30). Implantation was analogous to clinical annuloplasty, using 10 2-0 Ti·Cron sutures (Covidien, Dublin, Ireland) with suture bite approximately 10 mm wide and 1.5 mm deep (Figure 1). The transducers did not affect ring or suture function.2Siefert A.W. Pierce E.L. Lee M. Jensen M.Ø. Aoki C. Takebayashi S. et al.Suture forces in undersized mitral annuloplasty: novel device and measurements.Ann Thorac Surg. 2014; 98: 305-309Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar Animal care was provided in compliance with protocols approved by the Institutional Animal Care and Use Committee at University of Pennsylvania, in accordance with National Institutes of Health guidelines for humane care. The animal was weaned from cardiopulmonary bypass, and resting hemodynamics were reestablished. To investigate the impact of hypercontractility on annuloplasty suture tension, a 0.2-μg intravenous bolus of epinephrine was administered, causing a rise in LVP to 195 mm Hg over 30 to 40 seconds. Suture force within a cycle trended positively with LVP at every position (Figure 2). One suture, located between the trigones along the anterior aspect, experienced twice the peak loading of any other suture at all LVPs. At an LVP of 188 mm Hg, a dramatic decrease in force was observed at this position, from 16.7 N to 0.6 N. Simultaneously, peak forces increased at the 2 adjacent sutures, one by 3.1 N and the other by 2.6 N. Two other sutures experienced small increases (1.3 N and 0.3 N); but force decreased at all other sutures. After the animal was euthanized, visual examination revealed that the suture in question had torn through the annulus tissue, likely owing to technical misplacement above the annular hinge (Figure 1, D). The suture itself remained intact. The ruptured tissue was not examined histologically. This case provides the first quantification of a tensile force responsible for annuloplasty ring suture dehiscence in the beating heart. After a 16.7 N load induced dehiscence, a combined 5.7 N shifted to the 2 adjacent sutures. This observation provides a likely mechanism whereby a single problematic suture could induce a cascade of dehiscence at multiple anchor points, as observed clinically.3Ciobanu A.O. Griffin S.C. Bennett S. Vinereanu D. Catastrophic mitral prosthesis dehiscence diagnosed by three-dimensional transesophageal echocardiography.J Clin Ultrasound. 2014; 42: 249-251Crossref PubMed Scopus (7) Google Scholar A less eccentric redistribution of force across the remaining sutures may be preferable. Greater suture loads may be expected along the anterior annulus in general. Cyclic changes in the anterior annulus's saddle shape4Rausch M.K. Bothe W. Kvitting J.-P.E. Swanson J.C. Ingels Jr., N.B. Miller D.C. et al.Characterization of mitral valve annular dynamics in the beating heart.Ann Biomed Eng. 2011; 39: 1690-1702Crossref PubMed Scopus (55) Google Scholar due to aortic filling and fibrous trigone motion, as well as its denser collagen,5Gunning G.M. Murphy B.P. Determination of the tensile mechanical properties of the segmented mitral valve annulus.J Biomech. 2014; 47: 334-340Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar may augment overall suture tension in this region. Nonetheless, it is noteworthy that the observed force distribution was so highly concentrated on the single failed suture, even at lower LVPs. This case was likely a consequence of misplacement of the suture in question; we believe that placement too high above the annular hinge heightened suture tension by adding an out-of-plane force component at that position. Beyond suture placement, valve-specific anatomy and/or ring selection also may contribute to the risk of dehiscence. Degenerative or ischemic disease may further complicate loading dynamics and suture pullout thresholds. Ultimately, any steps during device selection, suture placement, and tie-down that minimize sharp force concentrations on single sutures will likely help ensure prosthesis security. To concretely identify such steps, an improved understanding of the factors that most directly relate to suture dehiscence risk is first necessary. These factors are the subjects of ongoing work. We thank Charles Bloodworth and Ikechukwu Okafor for data analysis and critical review. Mitral annuloplasty ring dehiscence: Optimal force distribution with flexible ringsThe Journal of Thoracic and Cardiovascular SurgeryVol. 152Issue 6PreviewWe read with great interest the case report by Pierce and colleagues1 describing the measurement of suture tension during mitral annuloplasty ring dehiscence in a beating-heart ovine model. In an induced hypercontractile state, they noted a high peak suture tension in the midtrigonal region that abruptly decreased with suture dehiscence. A significant increase in tension was then transferred instantaneously to the adjacent 2 sutures. The notion that ring dehiscence begins with a single point of increased tension that is sequentially distributed along the ring is intuitively appealing. Full-Text PDF Open Archive

The chordal structure is a part of mitral valve geometry that has been commonly neglected or simplified in computational modeling due to its complexity. However, these simplifications cannot be used when investigating the roles of individual chordae tendineae in mitral valve closure. For the first time, advancements in imaging, computational techniques, and hardware technology make it possible to create models of the mitral valve without simplifications to its complex geometry, and to quickly run validated computer simulations that more realistically capture its function. Such simulations can then be used for a detailed analysis of chordae-related diseases. In this work, a comprehensive model of a subject-specific mitral valve with detailed chordal structure is used to analyze the distinct role played by individual chordae in closure of the mitral valve leaflets. Mitral closure was simulated for 51 possible chordal rupture points. Resultant regurgitant orifice area and strain change in the chordae at the papillary muscle tips were then calculated to examine the role of each ruptured chorda in the mitral valve closure. For certain subclassifications of chordae, regurgitant orifice area was found to trend positively with ruptured chordal diameter, and strain changes correlated negatively with regurgitant orifice area. Further advancements in clinical imaging modalities, coupled with the next generation of computational techniques will enable more physiologically realistic simulations.

Authors have nothing to disclose with regard to commercial support. Authors have nothing to disclose with regard to commercial support. We thank Spratt and colleagues for their enthusiastic response1Spratt J.R. Spratt J.A. Lawrie G.M. Mitral annuloplasty ring dehiscence: optimal force distribution with flexible rings.J Thorac Cardiovasc Surg. 2016; 152: 1639Abstract Full Text Full Text PDF Scopus (4) Google Scholar to our case report.2Pierce E.L. Gentile J. Siefert A.W. Gorman R.C. Gorman J.H. Yoganathan A.P. Real-time recording of annuloplasty suture dehiscence reveals a potential mechanism for dehiscence cascade.J Thorac Cardiovasc Surg. 2016; 152: e15-e17Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar Our case report does not provide any direct evidence regarding the use of a flexible ring or running suture; however, we agree that it enforces the notion that more durable annuloplasty approaches may exist. The positive experience of these and other surgeons when using flexible annuloplasty rings secured via running suture suggests that this approach is worthy of increased consideration. We note that the use of numerous interrupted sutures may at least seem to offer greater durability than would a running suture. Whereas any break in a running suture leaves the entire ring unsecured, numerous mattress sutures offer a degree of redundancy against suture breakage. Yet, a previous study observed the ultimate tensile strength of 3-0 TiCron sutures to be 17.8 N, even after knotting3Viinikainen A. Göransson H. Huovinen K. Kellomäki M. Törmälä P. Rokkanen P. Material and knot properties of braided polyester (Ticron®) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 sutures.J Mater Sci Mater Med. 2006; 17: 169-177Crossref PubMed Scopus (23) Google Scholar; we recently showed interrupted suture holding strength in the ovine mitral annulus to be 4.9 ± 2.8 N (2-0 TiCron sutures).4Pierce E.L. Siefert A.W. Paul D.M. Wells S.K. Bloodworth C.H. Takebayashi S. et al.How local annular force and collagen density govern mitral annuloplasty ring dehiscence risk.Ann Thorac Surg. 2016; 102: 518-526Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar These facts establish tissue rupture, not suture breakage, as the likeliest mode of dehiscence and thus provide some mechanistic support to the running suture's durability. Spratt and colleagues have collectively performed a substantial volume of mitral valve repairs using flexible rings secured with running sutures, and their reported suture dehiscence outcomes are impressive. It is plausible that an optimally implanted ring using this technique is better able to distribute tension than is a rigid ring with interrupted sutures. To address this question with certainty, the expected suture forces should be quantified with a technique analogous to our latest reports.2Pierce E.L. Gentile J. Siefert A.W. Gorman R.C. Gorman J.H. Yoganathan A.P. Real-time recording of annuloplasty suture dehiscence reveals a potential mechanism for dehiscence cascade.J Thorac Cardiovasc Surg. 2016; 152: e15-e17Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar, 4Pierce E.L. Siefert A.W. Paul D.M. Wells S.K. Bloodworth C.H. Takebayashi S. et al.How local annular force and collagen density govern mitral annuloplasty ring dehiscence risk.Ann Thorac Surg. 2016; 102: 518-526Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar Indeed, we are underway studying the capacity for ring flexibility to relieve suture forces. Spratt and colleagues make a compelling case that the running suture should be investigated similarly. Our case report highlights the importance not only of the expected suture forces after a given annuloplasty approach but also of the robustness of that approach against suture misplacement. We observed that a small misplacement was sufficient to tear loose one mattress suture,2Pierce E.L. Gentile J. Siefert A.W. Gorman R.C. Gorman J.H. Yoganathan A.P. Real-time recording of annuloplasty suture dehiscence reveals a potential mechanism for dehiscence cascade.J Thorac Cardiovasc Surg. 2016; 152: e15-e17Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar even from what is typically the strongest segment of the annulus (the anterior aspect, between the trigones).4Pierce E.L. Siefert A.W. Paul D.M. Wells S.K. Bloodworth C.H. Takebayashi S. et al.How local annular force and collagen density govern mitral annuloplasty ring dehiscence risk.Ann Thorac Surg. 2016; 102: 518-526Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar Although the freedom from dehiscence reported by Spratt and colleagues is exciting, precision of suture placement may be of the greatest concern at lower-volume centers. Bolling and colleagues5Bolling S.F. Li S. O'Brien S.M. Brennan J.M. Prager R.L. Gammie J.S. Predictors of mitral valve repair: clinical and surgeon factors.Ann Thorac Surg. 2010; 90: 1904-1912Abstract Full Text Full Text PDF PubMed Scopus (249) Google Scholar have reported that, among all surgeons and hospitals in The Society of Thoracic Surgeons Adult Cardiac Surgery Database, the median number of isolated mitral procedures annually was 5. In this landscape, the most robust combination of ring type and suturing technique may prove most effective in preventing suture dehiscence. Thus far, the identification of such an optimum approach remains elusive. This study was partially supported by a fellowship from the National Science Foundation (DGE-1148903: ELP) and by a grant from the National Heart, Lung and Blood Institute (HL113216). Mitral annuloplasty ring dehiscence: Optimal force distribution with flexible ringsThe Journal of Thoracic and Cardiovascular SurgeryVol. 152Issue 6PreviewWe read with great interest the case report by Pierce and colleagues1 describing the measurement of suture tension during mitral annuloplasty ring dehiscence in a beating-heart ovine model. In an induced hypercontractile state, they noted a high peak suture tension in the midtrigonal region that abruptly decreased with suture dehiscence. A significant increase in tension was then transferred instantaneously to the adjacent 2 sutures. The notion that ring dehiscence begins with a single point of increased tension that is sequentially distributed along the ring is intuitively appealing. Full-Text PDF Open Archive

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 (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.

The diversity of mitral valve (MV) geometries and multitude of surgical options for correction of MV diseases necessitates the use of computational modeling. Numerical simulations of the MV would allow surgeons and engineers to evaluate repairs, devices, procedures, and concepts before performing them and before moving on to more costly testing modalities. Constructing, tuning, and validating these models rely upon extensive in vitro characterization of valve structure, function, and response to change due to diseases. Micro-computed tomography (\(\mu \)CT) allows for unmatched spatial resolution for soft tissue imaging. However, it is still technically challenging to obtain an accurate geometry of the diastolic MV. We discuss here the development of a novel technique for treating MV specimens with glutaraldehyde fixative in order to minimize geometric distortions in preparation for \(\mu \)CT scanning. The technique provides a resulting MV geometry which is significantly more detailed in chordal structure, accurate in leaflet shape, and closer to its physiological diastolic geometry. In this paper, computational fluid–structure interaction (FSI) simulations are used to show the importance of more detailed subject-specific MV geometry with 3D chordal structure to simulate a proper closure validated against \(\mu \)CT images of the closed valve. Two computational models, before and after use of the aforementioned technique, are used to simulate closure of the MV.