New Mitral Valve Annuloplasty Concept: Optimizing Annular Dynamics and Force Distribution.

BACKGROUND: Temporal three-dimensional (3D) analysis of the mitral valve biomechanics has prompted a re-evaluation of surgical approaches and repair device designs to accommodate the natural dynamics of the valve. Such new designs strive to obtain lower annulus restraining forces, resulting in more natural leaflet and chordal stresses. A new annuloplasty system was evaluated using 3D motion and out-of-plane force analysis. It was hypothesized that this system would not impact the valve with adverse motion restrictions or high systolic annular forces compared to conventional flat rigid ring designs. METHODS: In an acute porcine set-up, six 80 kg pigs were monitored before and after implantation of the new annuloplasty system consisting of two half-rings with a saddle-shaped outline. Valvular 3D dynamic geometry was obtained using sonomicrometry before and after annuloplasty system implantation. Strain gauges mounted on the commissural segments provided the annular restraining force distribution perpendicular to the annular plane. RESULTS: The change in annular height to commissural width ratio from diastole to systole did not alter following implantation (p >0.05). Out-of-plane systolic restraining forces were 0.2 ± 0.1 N and 0.8 ± 0.3 N (mean ± SEM) in the posterior and anterior commissural segments, respectively, without any difference in-between (p >0.1). Forces in both commissural segments were significantly lowered compared to previous measurements with a flat and stiff mitral annuloplasty ring (p <0.01). Mitral annular septal-lateral distance, area, and circumference in the commissural segments were decreased after implantation (p <0.05). The cross-annular distance between the commissural segments and the lengths of the anterior and posterior annular segments did not change following implantation (p >0.05). CONCLUSIONS: The new annuloplasty system design maintained annular 3D dynamics and provided a minimized out-of-plane restraining force distribution compared to earlier studies on flat rigid rings. This may have important implications in the selection of annuloplasty devices in order to increase repair durability.

Remodeling Mitral Annuloplasty Ring Concept with Preserved Dynamics of Annular Height.

BACKGROUND AND AIM OF THE STUDY: The configuration of the native annulus changes from nearly flat in the diastolic phase to saddle-shaped in the systolic phase. The present study was conducted to test a novel remodeling annuloplasty ring with built-in septal-lateral fixation and commissural axial flexibility so as to maintain the change in annular saddle shape. The study aim was to evaluate the in-vivo biomechanical performance of the novel annuloplasty ring, compared with the native valve and a semi-rigid and rigid annuloplasty ring. METHODS: All measurements were performed in vivo using a porcine model. A total of 28 pigs (bodyweight ca. 80 kg) were randomized to four groups: (i) with no ring; (ii) with a novel remodeling ring; (iii) with a semi-rigid ring (Physio I Ring, Edwards Lifesciences); and (iv) with a rigid ring (Classic Annuloplasty Ring, Edwards Lifesciences). Force measurements were performed using a dedicated transducer to determine remodeling capacity of the annuloplasty rings. Geometric parameters were measured by implanting sonomicrometry crystals along the mitral annulus. RESULTS: All ring groups significantly restricted the cyclic change of the mitral annulus compared with the 'no-ring' group. The change and maximum value of the annular height were maintained for the novel ring but were significantly decreased for the rigid and semi-rigid rings compared with the 'no-ring' group. Mitral annular force measurements confirmed that the overall remodeling capacity of the novel ring was comparable with the conventional ring groups, and significantly higher in the septal-lateral direction compared to the semi-rigid ring. CONCLUSIONS: In-vivo geometry and force measurements indicated that the intended design features of the new device were successfully provided. The novel ring concept with remodeling properties, combined with the advantages of a flexible annuloplasty ring, is unique. The maintenance of annular saddle shape and cyclic change in annular height may be an important step towards improved mitral valve repair.

Surgical Treatment of Functional Ischemic Mitral Regurgitation.

After myocardial infarction, functional ischemic mitral regurgitation (FIMR) is present in 21% of patients, and 3-13% have at least moderate FIMR. Currently, the 'gold-standard' treatment of FIMR is down-sized ring annuloplasty at the time of coronary artery bypass (CABG) surgery. However, this procedure has a failure rate of 20-30% in terms of recurrent FIMR after two to four years. In many ways, a cross-roads has been reached in terms of what constitutes optimal FIMR treatment: Is CABG combined with mitral valve ring annuloplasty better than CABG alone in moderate FIMR? Does mitral valve repair really produce better outcome than mitral valve replacement? And does adding an adjunct valvular repair or subvalvular left ventricular reverse remodeling procedure shift that balance? In order to shed further light on these questions and to help identify potential cornerstones in improving the 'gold standard' therapy, the present review addresses the current status and future perspectives of the surgical treatment of FIMR.

Papillary muscle force distribution after total tricuspid reconstruction using porcine extracellular matrix: in-vitro valve characterization.

BACKGROUND AND AIM OF THE STUDY: The use of extracellular matrix (ECM) from the porcine small intestinal submucosa has shown promising results in reconstructive heart surgery. The study aim was to compare native and ECM tricuspid valves with regards to tricuspid leaflet coaptation geometry and force development in the three papillary muscles, under normal ventricular pressures. METHODS: Six native porcine tricuspid valves and five ECM valves were examined in a static pressure right-heart simulator. Water was used in the ventricular chamber to induce adequate pressure changes (from 5 to 40 mmHg). Dedicated force transducers were used to measure force development in the three papillary muscles in parallel with ventricular pressure measurements. Relative leaflet area was defined as the percentage that one leaflet area comprised of the whole orifice area. The estimated peak leaflet pressure force was defined as leaflet area x peak ventricular pressure, and peak leaflet tethering force was calculated as the average of two adjacent papillary muscles forces. Valve competence and leaflet areas were documented using digital photography. RESULTS: The relative leaflet area of the anterior leaflet was significantly smaller (0.4 versus 0.5, p < 0.01) and that of the posterior leaflet was significantly larger (0.3 versus 0.2; p < 0.001) in ECM tube grafts compared to native valves. No difference was found between septal leaflet relative areas (p > 0.1). Accordingly, estimated peak leaflet pressure forces were greater in anterior leaflets and smaller in the posterior leaflets of native valves compared to ECM valves (p < 0.01). However, peak papillary muscle forces and peak leaflet tethering forces did not differ significantly between the valves. CONCLUSION: A competent and functional tricuspid valve can be constructed in vitro from ECM. In spite of different leaflet area distributions, the force distribution and tethering forces were not significantly different between the two valve types, indicating that a physiologically functioning tricuspid valve can be constructed from ECM.

Entire Mitral Valve Reconstruction Using Porcine Extracellular Matrix: Adding a Ring Annuloplasty.

PURPOSE: This study investigated the implications of inserting a flexible annuloplasty ring after reconstructing the entire mitral valve in a porcine model using a previously investigated tube graft design made of 2-ply small intestinal submucosa extracellular matrix (CorMatrix®). METHODS: An acute model with eight 80-kg pigs, each acting as its own control, was used. The entire mitral valve was reconstructed with a 2-ply small intestinal submucosa extracellular matrix tube graft (CorMatrix®). Subsequently, a Simulus® flexible ring was inserted. The characterization was based on mitral annular geometry and valvular dynamics with sonomicrometry and echocardiography. RESULTS: After adding the ring annuloplasty, the in-plane annular dynamics were more constant throughout the cardiac cycle compared to the reconstruction alone. However, the commissure-commissure distance was statistically significantly decreased [35.0 ± 3.4 mm vs. 27.4 ± 1.9 mm, P < 0.001, diff = - 7.6 mm, 95% CI, - 9.8 to (-5.4) mm] after ring insertion, changing the physiological annular D-shape into a circular shape which created folds at the coaptation zone resulting in a central regurgitant jet on color Doppler. CONCLUSION: We successfully reconstructed the entire mitral valve using 2-ply small intestinal submucosal extracellular matrix (CorMatrix®) combined with a flexible annuloplasty. The annuloplasty reduced the unphysiological systolic widening previously found with this reconstructive technique. However, the Simulus flex ring changed the physiological annular D-shape into a circular shape and hindered a correct unfolding of the leaflets. Thus, we do not recommend a flexible ring in conjunction with this reconstructive technique; further investigations are needed to discover a more suitable remodelling annuloplasty.

Mitral valve mechanics following posterior leaflet patch augmentation.

BACKGROUND AND AIM OF THE STUDY: Attention towards the optimization of mitral valve repair methods is increasing. Patch augmentation is one strategy used to treat functional ischemic mitral regurgitation (FIMR). The study aim was to investigate the force balance changes in specific chordae tendineae emanating from the posterior papillary muscle in a FIMR-simulated valve, following posterior leaflet patch augmentation. METHODS: Mitral valves were obtained from 12 pigs (body weight 80 kg). An in vitro test set-up simulating the left ventricle was used to hold the valves. The left ventricular pressure was regulated with water to simulate different static pressures during valve closure. A standardized oval pericardial patch (17 x 29 mm) was introduced into the posterior leaflet from mid P2 to the end of the P3 scallop. Dedicated miniature transducers were used to record the forces exerted on the chordae tendineae. Data were acquired before and after 12 mm posterior and 5 mm apical posterior papillary muscle displacement to simulate the effect from one of the main contributors of FIMR, before and after patch augmentation. RESULTS: The effect of displacing the posterior papillary muscle induced tethering on the intermediate chordae tendineae to the posterior leaflet, and resulted in a 39.8% force increase (p = 0.014). Posterior leaflet patch augmentation of the FIMR valve induced a 31.1% force decrease (p = 0.007). There was no difference in force between the healthy and the repaired valve simulations (p = 0.773). CONCLUSION: Posterior leaflet patch augmentation significantly reduced the forces exerted on the intermediate chordae tendineae from the posterior papillary muscle following FIMR simulation. As changes in chordal tension lead to a redistribution of the total stress exerted on the valve, patch augmentation may have an adverse long-term influence on mitral valve function and remodeling.

Surgical relocation of the papillary muscles in functional ischemic mitral regurgitation: what are the forces of the relocation stitches acting on the myocardium?

BACKGROUND AND AIM OF THE STUDY: In patients with chronic functional ischemic mitral regurgitation (FIMR), papillary muscle relocation has the potential to induce reverse left ventricular remodeling. However, in order to optimize function and durability, the forces imposed on the left ventricular myocardium by papillary muscle relocation should be assessed. METHODS: Eight pigs with FIMR were subjected to down-sized ring annuloplasty in combination with relocation of the anterior (5 mm) and posterior (15 mm) papillary muscles towards the respective trigone. Papillary muscle relocation was obtained by a 2-0 expanded polytetrafluoroethylene stitch fixed to the trigone, exteriorized through the myocardium overlying the papillary muscle, and fixed to an epicardial disc. Tension in these stitches was measured at a systolic blood pressure > 80 mmHg using a custom-made sliding caliper with a strain gauge mounted in line. This allowed assessment of the cyclic change from minimal diastolic to maximum systolic papillary muscle relocation stitch tension. RESULTS: Maximum cyclic change in the posterior papillary muscle (PPM) stitch tension was 1.1 N at 15 mm relocation. In comparison, the anterior papillary muscle (APM) tension was increased to a maximum of 1.4 N with only 5 mm relocation. Surprisingly, during each step of isolated PPM relocation, the APM stitch tension increased concomitantly, but in contrast APM relocation did not influence the magnitude of PPM stitch tension. There was no statistically significant difference between cyclic changes in APM and PPM stitch tension at any step of relocation. CONCLUSION: Papillary muscle relocation using stitches attached between epicardial discs and respective trigones induced a cyclic change in papillary muscle relocation stitch tension of 1.1-1.4 N. These values were in the range of normal tension in the mitral valve apparatus, and equivalent to only 19-24% of the total papillary muscle forces. Therefore, this technique does not appear to induce a non-physiologically high cyclic load on the mitral valve complex.

Annular and subvalvular dynamics after extracellular matrix mitral tube graft implantation in pigs.

OBJECTIVES: Entire mitral valve reconstruction with an extracellular matrix tube graft is a potential candidate to overcome the current limitations of mechanical and bioprosthetic valves. However, clinical data have raised concern with respect to patch failure. The aim of our study was to evaluate the impact of extracellular matrix mitral tube graft implantation on mitral annular and subvalvular regional dynamics in pigs. METHODS: A modified tube graft design made of 2-ply extracellular matrix was used (CorMatrix®; Cardiovascular Inc., Alpharetta, GA, USA). The reconstructions were performed in an acute 80-kg porcine model (N = 8), where each pig acted as its own control. Haemodynamics were assessed with Mikro-Tip pressure catheters and mitral annular and subvalvular geometry and dynamics with sonomicrometry. RESULTS: Catheter-based peak left atrial pressure and pressure difference across the mitral and aortic valves in the reconstructions were comparable to the values seen in the native mitral valves. Also comparable were maximum mitral annular area (755 ± 100 mm2), maximum septal-lateral distance (29.7 ± 1.7 mm), maximum commissure-commissure distance (35.0 ± 3.4 mm), end-systolic annular height-to-commissural width ratio (10.2 ± 1.0%) and end-diastolic interpapillary muscle distance (27.7 ± 3.3 mm). Systolic expansion of the mitral annulus was, however, observed after reconstruction. CONCLUSIONS: The reconstructed mitral valves were fully functional without regurgitation, obstruction or stenosis. The reconstructed mitral annular and subvalvular geometry and subvalvular dynamics were found in the same range to those in the native mitral valve. A regional annular ballooning effect occurred that might predispose to patch failure. However, the greatest risk was found at the papillary muscle attachments.

Impact of papillary muscle relocation as adjunct procedure to mitral ring annuloplasty in functional ischemic mitral regurgitation.

BACKGROUND: The optimal surgical treatment in functional ischemic mitral regurgitation (FIMR) remains controversial. Recently, a posterior papillary muscle relocation (PMR) technique as adjunct procedure to ring annuloplasty has been proposed to prevent recurrent FIMR. In the present study, we used 3D cardiac MRI to assess the impact of relocating both papillary muscles as adjunct procedure to downsized ring annuloplasty on mitral leaflet coaptation geometry in FIMR pigs. METHODS AND RESULTS: Eleven FIMR pigs were randomized to downsized ring annuloplasty (RA; n=6) or RA combined with PMR (RA+PMR, n=5). In the RA+PMR group, a 2-0 Gore-Tex suture was attached to each trigone, exteriorized through the corresponding papillary muscle, mounted on an epicardial pad, and tightened to relocate the myocardium adjacent to the anterior and posterior papillary muscles 5 and 15 mm, respectively. Using 3D MRI, the impact from these interventions on leaflet geometry was assessed. The distance from the posterior papillary muscle to the anterior trigone was reduced significantly more (median values) in the RA+PMR compared with RA animals at end-diastole (-7.9% versus 3.8%, P<0.01) and end-systole (-9.7% versus 2.5%, P=0.02). Accordingly, lateral tethering of the coaptation point (median values) was reduced significantly more in RA+PMR compared with RA animals (-42.8% versus -29.1%, P<0.01). CONCLUSIONS: Adding papillary muscle relocation to downsized ring annuloplasty reduced lateral leaflet tethering in a porcine experimental model of FIMR. Therefore, this technique holds promise for reducing persistent and recurrent FIMR in patients.

Does down-sized ring annuloplasty induce papillary muscle relocation in ischemic mitral regurgitation?

BACKGROUND AND AIM OF THE STUDY: Down-sized ring annuloplasty has been shown to induce left ventricular remodeling in patients with functional ischemic mitral regurgitation (FIMR). To determine if this remodeling comprised papillary muscle (PM) relocation, a chronic FIMR porcine model was used to assess the impact on three-dimensional (3D) PM positioning, by implanting a down-sized rigid ring annuloplasty. METHODS: Six out of ten FIMR pigs that underwent a down-sized mitral ring annuloplasty (CE Classic size 26-28) survived for six weeks postoperatively. 3D cardiac magnetic resonance imaging was carried out at one week preoperatively, and repeated at one and six weeks postoperatively, to assess the direct distances (in mm) from the anterior papillary muscle (APM) and posterior papillary muscle (PPM) to each trigone. Three reference planes were also constructed to determine APM and PPM displacement in the lateral, anterioposterior, and apical directions. RESULTS: Relative to the preoperative situation, at one week postoperatively a reduced displacement of the APM was observed in an anterior direction (from 18.8 to 16.2 mm; p < 0.05) and from the posterior trigone (from 40.5 to 37.4 mm; p < 0.05) at end-diastole. Relative to one week postoperatively, at six weeks postoperatively a reduced PPM displacement was observed from the anterior trigone (43.0 versus 42.0 mm; p < 0.05) at end-systole. Relative to the preoperative situation, no overall tendency of surgically induced PM relocation was observed at one or six weeks postoperatively. CONCLUSION: A down-sized ring annuloplasty did not induce an overall pattern of PM relocation in pigs with chronic FIMR.

Mitral Valve Posterior Leaflet Reconstruction Using Extracellular Matrix: In Vitro Evaluation.

PURPOSE: To investigate the anatomical and functional effects of complete surgical reconstruction of the posterior mitral leaflet and associated chordae tendineae with a patch made of 2-ply small intestinal submucosal extracellular matrix in vitro. METHODS: Seven explanted mitral valves with intact subvalvular apparatus from 80-kg pigs were evaluated in a left heart simulator and served as their own controls. After testing the native valve, the mitral posterior leaflet and associated chordae tendineae were excised and reconstructed by using the 2-ply small intestinal submucosa extracellular matrix patch. The characterization of the reconstruction was based on geometric data from digital images, papillary muscle force, annular tethering force and leaflet pressure force. RESULTS: The reconstructed valves were fully functional without regurgitation, tearing or rupture during incrementally increased pressure from 0 to 120 mmHg. The leaflet areas were preserved after reconstruction, with a normal configuration of the coaptation line. However, the coaptation midpoint moved posteriorly after reconstruction (A2: 15.8 ± 1.4 vs. 18.9 ± 1.5 mm, p = 0.002, diff = 3.1 mm, 95% CI 1.3 to 4.8 mm). The anterior papillary muscle force increased significantly (3.9 vs. 4.6 N, p = 0.029, diff = 0.7 N, 95% CI 0.1 to 1.4 N at 120mmHg) after reconstruction. The posterior papillary muscle force, leaflet pressure force and annular pressure force did not change significantly. CONCLUSIONS: In this in vitro model, mitral valve anatomy and function were comparable between the native mitral valve and our new surgical technique for complete reconstruction of the posterior mitral leaflet and associated chordae tendineae. These promising results warrant further in vivo evaluation.

Annular Dynamics and Leaflet Geometry in Patch Reconstruction of the Posterior Mitral Leaflet After Adding a Flexible Annuloplasty Ring.

PURPOSE: Patch reconstruction of the posterior mitral leaflet using small intestinal submucosa extracellular matrix has been successfully performed in a porcine study. The patch reconstruction, however, resulted in non-physiological systolic widening of the mitral annulus, suggesting the need for an annuloplasty ring. The objective was to characterize the impact on annular dynamics and leaflet geometry of adding a flexible annuloplasty ring to the posterior mitral leaflet patch reconstruction. METHODS: Measurements were performed in an acute 80-kg porcine model, with seven pigs acting as their own controls. The posterior mitral leaflet was reconstructed with a 2-ply small intestinal submucosa extracellular matrix patch (CorMatrix®). Additionally, a Simulus® Flexible Annuloplasty Ring (Medtronic Inc., Minneapolis, MN, USA) was inserted. Mitral annular dynamics were evaluated using sonomicrometry, and leaflet geometry was described using echocardiography. RESULTS: The annuloplasty ring reduced mitral annular dimensions and restricted cyclic changes in mitral annular area (126 ± 19 vs. 30 ± 13 mm2, p < 0.001), septal-lateral and commisure-commisure distances. Ring annuloplasty prevented systolic widening in the mitral annulus after posterior mitral leaflet reconstruction. The annular saddle shape and leaflet coaptation length (8.7 ± 2.3 vs. 9.7 ± 1.3 mm, p = 0.221) were comparable before and after ring insertion. CONCLUSIONS: The flexible annuloplasty ring resulted in a downsized annulus with restriction of cyclic annular changes in the reconstructed mitral valve. Ring insertion preserved the annular saddle shape and coaptation length. The ring annuloplasty counteracted the non-physiological annular dynamics, and this may improve durability of the posterior mitral leaflet patch reconstruction.

Entire mitral reconstruction with porcine extracellular matrix in an acute porcine model.

OBJECTIVE: The objective of our study was to investigate the feasibility of reconstructing the entire mitral valvular and subvalvular apparatus in pigs using a modified tube graft design made of 2-ply small intestinal submucosa extracellular matrix. METHODS: The reconstructions were performed in an acute 80-kg porcine model with 8 pigs, each acting as its own control. A modified tube graft was designed from a sheet of 2-ply small intestinal submucosa extracellular matrix. Before and after mitral valve reconstruction, echocardiography was used to assess mitral regurgitation, left ventricular outflow tract obstruction due to systolic anterior motion, mitral stenosis, leaflet mobility, and leaflet geometry. RESULTS: The reconstructed mitral valves were fully functional without any observable echocardiographic signs of regurgitation. We did not observe any left ventricular outflow tract obstruction due to systolic anterior motion nor any mitral valve stenosis, despite a diminished septal-lateral distance after reconstruction. The reconstruction had a reduced tenting area, a reduced coaptation length (9.6 ± 1.7 mm vs 7.9 ± 1.0 mm, P = .010, diff = -1.7 mm, 95% confidence interval, -3.1 to -0.4 mm), and atrial bending of both leaflets. CONCLUSIONS: In this acute porcine study, entire mitral valvular and subvalvular apparatus reconstruction using a modified tube graft design made from 2-ply small intestinal submucosal extracellular matrix was feasible. The 2-ply small intestinal submucosa extracellular matrix could withstand the pressure exerted by the left ventricle without any signs of tearing or rupture. These promising results warrant further assessment of both the annular geometry and the long-term durability.

Saddle-shaped mitral valve annuloplasty rings experience lower forces compared with flat rings.

BACKGROUND: New insight into the 3D dynamic behavior of the mitral valve has prompted a reevaluation of annuloplasty ring designs. Force balance analysis indicates correlation between annulus forces and stresses in leaflets and chords. Improving this stress distribution can intuitively enhance the durability of mitral valve repair. We tested the hypothesis that saddle-shaped annuloplasty rings have superior uniform systolic force distribution compared with a nonuniform force distribution in flat annuloplasty rings. METHODS AND RESULTS: Sixteen 80-kg pigs had a flat (n=8) or saddle-shaped (n=8) mitral annuloplasty ring implanted. Mitral annulus 3D dynamic geometry was obtained with sonomicrometry before ring insertion. Strain gauges mounted on dedicated D-shaped rigid flat and saddle-shaped annuloplasty rings provided the intraoperative force distribution perpendicular to the annular plane. Average systolic annular height to commissural width ratio before ring implantation was 14.0%+/-1.6%. After flat and saddle shaped ring implantation, the annulus was fixed in the diastolic (9.0%+/-1.0%) and systolic (14.3%+/-1.3%) configuration, respectively (P<0.01). Force accumulation was seen from the anterior (0.72N+/-0.14N) and commissural annular segments (average 1.38N+/-0.27N) of the flat rings. In these segments, the difference between the 2 types of rings was statistically significant (P<0.05). The saddle-shaped annuloplasty rings did not experience forces statistically significantly larger than zero in any annular segments. CONCLUSIONS: Saddle-shaped annuloplasty rings provide superior uniform annular force distribution compared to flat rings and appear to represent a configuration that minimizes out-of-plane forces that could potentially be transmitted to leaflets and chords. This may have important implications for annuloplasty ring selections.

Mitral annuloplasty ring with selective flexibility for septal-lateral contraction and remodelling properties.

OBJECTIVES: To develop and evaluate a novel mitral annuloplasty ring with selective flexibility for septal-lateral contraction and rigidity for septal-lateral dilatation in an acute porcine model. METHODS: The novel mitral annuloplasty ring was designed with slits in the luminal posterior segment and annular lateral segments. The slits were designed to allow inward motion during contraction and to block outward motion during dilation. The novel mitral annuloplasty ring was tested in vitro with a dedicated mechanical test bench, followed by in vivo characterization, using sonomicrometry and echocardiography for annular and leaflet geometry, in an acute porcine model. RESULTS: From the in vitro characterization, we verified that the ring could easily contract (0.7 mm/N) in the septal-lateral dimension, while dilatation was restrained (0.4 mm/N). In vivo characterization showed a cyclic range of 2.8 ± 0.0 mm for septal-lateral contraction. CONCLUSIONS: A novel saddle-shaped remodelling mitral annuloplasty ring was developed with selective flexibility for septal-lateral contraction and rigidity for septal-lateral dilatation. The advantages of this specific ring is that it re-establishes the coaptation plane, ensures leaflet mobility and septal-lateral flexibility and at the same time improves tissue adaptation and thereby decreases the risk of ring dehiscence and redilatation of the mitral annulus. This concept may prove beneficial for patients with ischaemic mitral valve regurgitation or degenerative valve disease.

Biomechanical characterization and comparison of different aortic root surgical techniques.

OBJECTIVES: Understanding the biomechanical impact of aortic valve-sparing techniques is important in an era in which surgical techniques are developing and are increasingly being used based on biomechanical understanding that is essential in the refining of existing techniques. The objective of this study was to describe how the valve-sparing remodelling (Yacoub) and reimplantation (David Type-1) techniques affect the biomechanics of the native aortic root in terms of force distribution and geometrical changes. METHODS: Two force transducers were implanted into 22 pigs, randomized to 1 of 3 groups (David = 7, native = 7 and Yacoub = 8) along with 11 sonomicrometry crystals and 2 pressure catheters. Force and geometry data were combined to obtain the local structural stiffness in different segments of the aortic root. RESULTS: The radial structural stiffness was not different between groups (P = 0.064) at the annular level; however, the David technique seemed to stabilize the aortic annulus more than the Yacoub technique. In the sinotubular junction, the native group was more compliant (P = 0.036) with the right-left coronary segment than the intervention groups. Overall, the native aortic root appeared to be more dynamic at both the annular level and the sinotubular junction than both intervention groups. CONCLUSIONS: In conclusion, the David procedure may stabilize the aortic annulus more than the Yacoub procedure, whereas the leaflet opening area was larger in the latter (P = 0.030). No difference (P = 0.309) was found in valve-opening delay between groups. The 2 interventions show similar characteristics at the sinotubular junction, whereas the David technique seemed more restrictive at the annular level than the Yacoub technique.

Entire mitral valve reconstruction using porcine extracellular matrix: static in vitro evaluation.

OBJECTIVES: To investigate the feasibility of reconstruction of the entire mitral valve using a tube graft made of 2-ply small intestinal submucosa extracellular matrix in vitro. METHODS: Seven explanted mitral valves with intact subvalvular apparatus from 80 kg pigs were evaluated in a left heart simulator and served as controls. After testing the native valve, the leaflets and chordae tendineae were explanted, and the 2-ply small intestinal submucosa extracellular matrix (CorMatrix®; Cardiovascular Inc., Alpharetta, GA, USA) tube graft was implanted. The characterization was based on geometric data from digital images, papillary muscle force, annular tethering force and leaflet pressure force. RESULTS: The tube grafts were fully functional without any signs of leakage, tearing or rupture during incrementally increased pressures from 0 mmHg to 120 mmHg. The posterior leaflet moved anteriorly and became larger after reconstruction when compared with the native valve. However, the mid coaptation point was preserved. The anterior papillary muscle force decreased significantly (5.2 N vs 4.4 N, P = 0.022 at 120 mmHg), and the posterior papillary muscle force increased significantly (4.8 N vs 5.6 N, P = 0.017 at 120 mmHg) after reconstruction. CONCLUSIONS: The entire mitral valvular and subvalvular reconstruction with a 2-ply small intestinal submucosa extracellular matrix tube graft is feasible in an in vitro model. Our method of reconstruction increased the convexity of the anterior leaflet's coaptation line and significantly redistributed the papillary muscle force towards the posterior papillary muscle. These promising results and the prospect of the entire mitral valvular and subvalvular reconstruction warrant further in vivo evaluations.

Effect of chronotropy and inotropy on stitch tension in the edge-to-edge mitral repair.

BACKGROUND: Our prior studies suggest that mitral annular septal-lateral (SL) diameter is the chief determinant of "Alfieri stitch" tension, but hemodynamic parameters may also play a role. We approximated the central edge of the mitral leaflets with a miniature force transducer to measure tension (T) at the leaflet approximation point during inotropic and chronotropic stimulation. METHODS AND RESULTS: Eight sheep were studied under open-chest conditions immediately after surgical placement of a miniature force transducer to approximate the leaflets and implantation of radiopaque markers on the LV and mitral annulus (MA). Chronotropic stimulation was induced with atrial pacing at 130 minutes(-1) (n=5) whereas inotropic state was increased with i.v. CaCl2 bolus (n=8). Hemodynamic data, stitch tension, and 3-D marker coordinates were obtained throughout the cardiac cycle before and during each intervention. Peak stitch tension (T(MAX)) under all conditions was observed in diastole and temporally correlated with peak annular SL (SL(MAX)) size. Atrial pacing did not change peak transducer tension or annular size. Calcium infusion also did not alter peak transducer tension (0.29+/-0.11 versus 0.32+/-0.10 N; P=NS) and only slightly reduced SL dimension (29.9+/-3.3 versus 29.3+/-3.5 mm; P<0.05). CONCLUSION: Isolated increase in heart rate or inotropic state did not alter peak stitch tension whereas enhanced contractile state decreased SL diameter minimally. These data, combined with those from our previous study, suggest that geometric (SL diameter) rather than hemodynamic parameters are the main determinants of "Alfieri stitch" tension. This implies that any interventional or surgical edge-to-edge repair performed without concomitant annular reduction to limit the SL dimension could expose the leaflet junction to forces which could limit repair durability.

Geometric determinants of chronic functional ischemic mitral regurgitation: insights from three-dimensional cardiac magnetic resonance imaging.

BACKGROUND AND AIM OF THE STUDY: The assessment of three-dimensional (3-D) mitral valve geometry in patients with chronic functional ischemic mitral valve regurgitation (FIMR) has been hampered by a lack of adequate imaging techniques. The study aim was to use a clinically applicable cardiac magnetic resonance imaging (MRI) technique to assess the 3-D mitral annular, leaflet and papillary muscle geometry in pigs with chronic FIMR. METHODS: Ten pigs with moderate chronic FIMR induced by catheter-based coiling of the circumflex artery, were examined using cardiac MRI. The reconstruction of 3-D data from two-dimensional cardiac MRI scans allowed the mitral annulus and leaflet geometries to be assessed. Using 3-D morphology scans, the spatial position of the posterior papillary muscle (PPM) relative to the anterior papillary muscle (APM), mitral annulus and anterior (A-trig) and posterior (P-trig) trigones was assessed. Using dedicated software for image analysis, data were transferred to a Cartesian coordinate system (x,y,z) for geometric analysis. Ten healthy pigs served as controls. RESULTS: Compared to controls, at end-systole in the chronic FIMR group the PPM was significantly displaced (p <0.05) from the APM (38 +/- 2 versus 23 +/- 1 mm), A-trig (48 +/- 2 versus 36 +/- 1 mm) and P-trig (41 +/-1 versus 33 +/- 1 mm). There was no significant apical PPM displacement (20 +/- 2 versus 20 +/- 1 mm). The annular area (1,240 +/- 90 versus 850 +/- 90 mm2), septolateral distance (36 +/- 2 versus 26 +/- 1 mm), commissure-to-commissure distance (38 +/- 2 versus 33 +/- 1 mm), mean tenting height (8 +/- 1 versus 5 +/- 0 mm), maximum tenting height (10 +/- 1 versus 7 +/- 0 mm), tenting volume (2,600 +/- 400 versus 1,500 +/- 200 mm3), and occlusional leaflet area (1,820 +/- 110 versus 1,120 +/- 70 mm2) were each significantly increased. CONCLUSION: This clinically applicable cardiac MRI modality permitted a detailed geometric insight to be made into the mitral annular, leaflet and PPM geometries that cause FIMR. Such a reliable tool for geometric mitral valve analysis has previously been demonstrated only by using invasive techniques. Hence, this approach holds promise for further clarifying the pathogenesis of chronic FIMR and improving preoperative surgical planning.

What forces act on a flat rigid mitral annuloplasty ring?

BACKGROUND AND AIM OF THE STUDY: Increasing mitral valve repair durability requires successful restoration and support with annuloplasty rings. The stress distribution in these devices indirectly determines the success of the repair. It is hypothesized that changes in annular geometry throughout the cardiac cycle result in adverse strain distribution in stiff, flat annuloplasty rings, and hence non-physiological loading of the myocardium. The study aim was to identify the three-dimensional (3-D) force distribution in mitral annuloplasty rings. METHODS: Eight animals were included in an acute porcine study. The mitral annulus 3-D dynamic geometry was assessed with sonomicrometry prior to ring insertion. Strain gauges mounted on dedicated D-shaped rigid flat annuloplasty rings enabled dynamic force measurements to be made perpendicular to the annulus plane. RESULTS: The average systolic annular height to commissural width ratio before ring implantation was 13.7 +/- 1.4%. Following ring implantation, the annulus was fixed in the diastolic flat configuration (p <0.01). Force accumulation was seen from the anterior (0.7 +/- 0.4 N) and commissural (1.4 +/- 1.0 N) annular segments; both forces were acting in opposite directions and were statistically significantly larger than zero (p <0.01; n = 8). CONCLUSION: These data demonstrate highest strains at the anterior and commissural areas of flat mitral annuloplasty rings, and support the hypothesis that the mitral valve annulus and its attached valvular and subvalvular structures apply systolic torque onto the flat annuloplasty ring in an attempt to conform it into the saddle-shaped configuration.