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

2016 
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 (F C ) that acts on sutures during cardiac contraction was measured with custom transducers. F C was measured at ten suture positions, throughout cardiac cycles with peak left ventricular pressure (LVP max ) 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 F C exceeded posterior F C at each LVP max (eg, 2.8 ± 1.3 N versus 1.8 ± 1.2 N at LVP max  = 125 mm Hg, p p C at LVP max 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 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.
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