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Background: Annuloplasty ring dehiscence is a well described mode of mitral valve repair failure. Defining the mechanisms underlying dehiscence may facilitate its prevention., Methods: Factors that govern suture dehiscence were examined with an ovine model. After undersized ring annuloplasty in live animals (n = 5), cyclic force (FC) that acts on sutures during cardiac contraction was measured with custom transducers. FC was measured at ten suture positions, throughout cardiac cycles with peak left ventricular pressure (LVPmax) of 100, 125, and 150 mm Hg. Suture pullout testing was conducted on explanted mitral annuli (n = 12) to determine suture holding strength at each position. Finally, relative collagen density differences at suture sites around the annulus were assessed by two-photon excitation fluoroscopy., Results: Anterior FC exceeded posterior FC at each LVPmax (eg, 2.8 ± 1.3 N versus 1.8 ± 1.2 N at LVPmax = 125 mm Hg, p < 0.01). Anterior holding strength exceeded posterior holding strength (6.4 ± 3.6 N versus 3.9 ± 1.6 N, p < 0.0001). On the basis of FC at LVPmax of 150 mm Hg, margin of safety before suture pullout was vastly higher between the trigones (exclusive) versus elsewhere (4.8 ± 0.9 N versus 1.9 ± 0.5 N, p < 0.001). Margin of safety exhibited strong correlation to collagen density (R(2) = 0.947)., Conclusions: Despite lower cyclic loading on posterior sutures, the weaker posterior mitral annular tissue creates higher risk of dehiscence, apparently because of reduced collagen content. Sutures placed atop the trigones are less secure than predicted, because of a combination of reduced collagen and higher overall rigidity in this region. These findings highlight the inter-trigonal tissue as the superior anchor and have implications on the design and implantation techniques for next-generation mitral prostheses., (Copyright © 2016 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Purpose: To demonstrate the first use of a novel technology for quantifying suture forces on annuloplasty rings to better understand the mechanisms of ring dehiscence., Description: Force transducers were developed, attached to a size 24 Physio ring, and implanted in the mitral annulus of an ovine animal. Ring suture forces were measured after implantation and for cardiac cycles reaching peak left ventricular pressures (LVP) of 100, 125, and 150 mm Hg., Evaluation: After implantation of the undersized ring to the flaccid annulus, the mean suture force was 2.0±0.6 N. During cyclic contraction, the anterior ring suture forces were greater than the posterior ring suture forces at peak LVPs of 100 mm Hg (4.9±2.0 N vs 2.1±1.1 N), 125 mm Hg (5.4±2.3 N vs 2.3±1.2 N), and 150 mm Hg (5.7±2.4 N vs 2.4±1.1 N). The largest force was 7.4 N at 150 mm Hg., Conclusions: The preliminary results demonstrate trends in annuloplasty suture forces and their variation with location and LVP. Future studies will significantly contribute to clinical knowledge by elucidating the mechanisms of ring dehiscence while improving annuloplasty ring design and surgical repair techniques., (Copyright © 2014 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Background: This study was undertaken to evaluate an in vitro mitral valve (MV) simulator's ability to mimic the systolic leaflet coaptation, regurgitation, and leaflet mechanics of a healthy ovine model and an ovine model with chronic ischemic mitral regurgitation (IMR)., Methods: Mitral valve size and geometry of both healthy ovine animals and those with chronic IMR were used to recreate systolic MV function in vitro. A2-P2 coaptation length, coaptation depth, tenting area, anterior leaflet strain, and MR were compared between the animal groups and valves simulated in the bench-top model., Results: For the control conditions, no differences were observed between the healthy animals and simulator in coaptation length (p = 0.681), coaptation depth (p = 0.559), tenting area (p = 0.199), and anterior leaflet strain in the radial (p = 0.230) and circumferential (p = 0.364) directions. For the chronic IMR conditions, no differences were observed between the models in coaptation length (p = 0.596), coaptation depth (p = 0.621), tenting area (p = 0.879), and anterior leaflet strain in the radial (p = 0.151) and circumferential (p = 0.586) directions. MR was similar between IMR models, with an asymmetrical jet originating from the tethered A3-P3 leaflets., Conclusions: This study is the first to demonstrate the effectiveness of an in vitro simulator to emulate the systolic valvular function and mechanics of a healthy ovine model and one with chronic IMR. The in vitro IMR model provides the capability to recreate intermediary and exacerbated levels of annular and subvalvular distortion for which IMR repairs can be simulated. This system provides a realistic and controllable test platform for the development and evaluation of current and future IMR repairs., (Copyright © 2013 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Background: Ischemic mitral valve (MV) repair for patients with severe left ventricular dilation remains challenging. The objective of this study was to investigate the efficacy of papillary muscle (PM) relocation to restore physiologic MV function., Methods: Fresh ovine MVs (n = 6) were studied in a left-heart simulator under physiologic hemodynamics. Ischemic MV disease was simulated by annular dilation and PM displacement. Initial valvular repair was performed with mitral annuloplasty; further PM displacement simulated progressive left ventricular dilation. Basal PM repositioning (Kron procedure), performed to alleviate leaflet tethering, consisted of relocating (1) both PMs toward the commissures; (2) both PMs toward the trigones; (3) the posteromedial PM toward the ipsilateral commissure; and (4) the posteromedial PM toward the ipsilateral trigone. Coaptation length and tenting area were measured using three-dimensional echocardiography as surrogates of MV function., Results: Papillary muscle relocation as an adjunct to mitral annuloplasty statistically improved coaptation length and tenting area compared with the disease condition. No statistical differences in coaptation length and tenting area were observed between final repaired conditions and control conditions. No statistical differences were observed between commissural and trigonal repairs at any incremental repair step. Coaptation length and tenting area were plotted against PM distance; the data were fit to linear regressions., Conclusions: In a realistic in vitro model of ischemic left ventricular dilation, apical-basal PM relocation, as an adjunct procedure to mitral annuloplasty, restored optimal MV closure. Trigonal or commissural traction suture location did not significantly affect the degree of restored coaptation. Linear relationships between PM positions and leaflet variables were established, which could be used to inform surgical repairs., (Copyright © 2013 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Background: Percutaneous edge-to-edge mitral valve (MV) repair is a potential therapeutic option for patients presenting with mitral regurgitation, who may not be suitable for surgery. We characterized the edge-to-edge repair forces in a posterior leaflet flail MV model to identify potential modes of mechanical failure., Methods: Porcine MVs were evaluated in two different sizes (Physio II 32 and 40) in a left-side heart simulator under physiologic hemodynamic conditions. Edge-to-edge repair was simulated by suturing miniature force transducers near the free edge of the anterior and posterior leaflets, on the ventricular side, resulting in a double orifice MV. Posterior leaflet flail was created by selective chordal cutting., Results: Chordal cutting resulted in posterior leaflet flail and mitral regurgitation; all valves coapted normally before chordal cutting. Peak systolic control forces (size 32, 0.098 ± 0.058 N; size 40, 0.236 ± 0.149 N) were not significantly different from systolic flail forces (size 32, 0.136 ± 0.107 N; size 40, 0.220 ± 0.128 N) for either MV size. No correlation was observed between force magnitude and flail height or width. Peak systolic force was greater (p = 0.08) for the larger MVs (size 40 compared with size 32). Finally, peak diastolic force was significantly smaller (p = 0.04) than peak systolic force regardless of valve size., Conclusions: For the first time, forces imparted on an edge-to-edge MV repair were quantified for a posterior leaflet flail model. Force magnitude was not significantly altered with flail compared with control; it was greatest during peak systole and increased with valve size., (Copyright © 2012 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Background: Limited knowledge exists regarding the forces that act on devices implanted in the mitral annulus. Determining the peak magnitudes, directions, rates, variation throughout the cardiac cycle, and change with left ventricular pressure (LVP) will aid in device development and evaluation., Methods: Novel transducers with the ability to measure forces in the septal-lateral and transverse directions were implanted in six healthy ovine subjects. Forces were measured for cardiac cycles reaching a peak LVP of 90, 125, 150, 175, and 200 mm Hg., Results: The septal-lateral force was observed to significantly increase from 3.9 ± 0.8 N (90) to 5.2 ± 1.0 N (125) p < 0.001, 5.9 ± 0.9 N (150) p < 0.001, 6.4 ± 1.2 N (175) p < 0.001, and 6.7 ± 1.5 N (200 mm Hg) p < 0.001. Similarly, the transverse force was seen to increase from 2.6 ± 0.6 N (90) to 3.8 ± 1.0 N (125) p < 0.01, 4.6 ± 1.3 N (150) p < 0.001, 4.3 ± 1.2 N (175) p < 0.001, and 3.5 ± 0.7 N (200 mm Hg) p < 0.05. In comparison, the septal-lateral force was significantly greater than the transverse force at 90 (p < 0.05), 125 (p < 0.05), 175 (p < 0.001), and 200 mm Hg (p < 0.0005)., Conclusions: Annular forces and their variations with LVP through the cardiac cycle are described. The results demonstrate differences in force magnitude and rate for increasing levels of LVP between the septal-lateral and transverse directions. These directional differences have strong implications in the development of future mitral devices., (Copyright © 2012 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)