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Annuloplasty Ring Suture Forces Differ By Ring Type In An IMR Diseased Ovine Model
Sanchita S. Bhat1, Katelynne Berland1, Andrew W. Siefert1, Maeve Janecka1, Shelley Chee-Mei Gooden1, Beatrice E. Ncho1, Takayuki Kawashima2, Mori Kazuki2, Satoshi Kozaki2, Robert C. Gorman2, Joseph H. Gorman, III2, Ajit Yoganathan1.
1Georgia Institute of Technology, Atlanta, GA, USA, 2University of Pennsylvania, Philadelphia, PA, USA.

OBJECTIVE: Ring annuloplasty are common interventions for ischemic mitral regurgitation (IMR). Rigid rings have been shown to optimize leaflet stress while flexible rings are believed to reduce suture forces. Despite this, ring dehiscence is a well described repair failure mode for both. We hypothesized that hybrid rings with a rigid anterior and flexible posterior segment could re-establish leaflet geometry while optimizing suture forces.
METHODS: Fifteen healthy sheep were subject to a posterior myocardial infarction involving ~ 20% of the left ventricular wall, including the posterior papillary muscle. In all animals, IMR developed over 6-8 weeks with asymmetric annular dilatation and subvalvular leaflet tethering. Rigid saddle (N=7), flexible (N=5) and hybrid (N=3) annuloplasty rings were instrumented with force transducers to quantify cyclic forces acting on each annuloplasty suture. Suture forces were cyclically measured for peak left ventricular pressures (LVP) of 100, 125, and 150 mmHg. Data was analyzed and compared between ring types and increasing LVPs.
RESULTS: Annuloplasty ring implantation eliminated MR in all animals. Cyclic suture forces were markedly larger on the posterior (5 o'clock) region of the rigid ring compared to hybrid and flexible rings. Ring forces were larger over the anterior annulus for the flexible and hybrid rings compared to rigid rings though the increase was less pronounced for the hybrid ring. To augment this data, additional experiments with hybrid ring types are being generated.
CONCLUSIONS: Fully flexible and hybrid rings tended to distribute forces to the more robust tissue (anterior) away from sutures anchored to the weaker tissue (posterior) compared to rigid rings. The hybrid and flexible rings seemed to lessen posterior forces while increasing anterior forces. These data indicate that hybrid rings may increase IMR repair durability by optimizing both leaflet stress and annular suture force distribution.


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