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Annuloplasty Suture Forces: Preliminary Insight for Identifying the Mechanisms of Ring Dehiscence
Eric L. Pierce, B.S.1, Andrew W. Siefert, M.S.2, Madonna Lee, M.D.3, Chikashi Aoki, M.D.3, Robert C. Gorman, M.D.3, Joseph H. Gorman, M.D.3, Ajit P. Yoganathan, Ph.D.1.
1Georgia Institute of Technology and Emory University, Atlanta, GA, USA, 2Georgia Institute of Technology, Atlanta, GA, USA, 3University of Pennsylvania, Philadelphia, PA, USA.

OBJECTIVE: An increasingly acknowledged short-term repair failure for functional mitral regurgitation is annuloplasty ring dehiscence. Though often attributed to surgical technique, no studies have identified whether suture failure, knot failure, or annular tissue tearing is the primary cause of dehiscence. To explore these mechanisms, this study aimed to demonstrate the first use of a novel technology to quantify suture forces for undersized mitral annuloplasty rings.
METHODS: Force transducers were developed and attached (N=10) to size 24 PhysioTM rings. Under cardiopulmonary bypass, instrumented rings were implanted in the mitral annuli of healthy ovine animals (N=4). Each transducer was secured to the annulus with a single mattress suture by the exact process used in normal ring implantation. Post-cardiopulmonary bypass, suture forces were measured continuously over cardiac cycles reaching peak left ventricular pressures (LVP) of 100, 125, and 150mmHg.
RESULTS: The mitral annulus of each animal (62±10kg) was successfully undersized by two ring sizes. Annuloplasty increased the diastolic transmitral pressure gradient by approximately 3mmHg in each animal. Averaged across all sutures, cyclic forces (calculated as the difference between peak and minimum force over each cycle) were observed to increase from 1.6±1.1N (100mmHg), to 1.9±1.2N (125mmHg), to 2.0±1.4N (150mmHg). At all levels of peak LVP, suture forces were greatest at the left and right fibrous trigones. Analyzing suture forces by region, those between the trigones exceeded those on the ring's posterior aspect. Among all studies, cyclic suture forces fell between 0.1-6.4N.
CONCLUSIONS: Undersized mitral annuloplasty suture forces were measured for the first time in a healthy ovine model. These forces reveal trends according to both suture position and LVP. Future studies will utilize these devices to evaluate suture forces in the settings of functional mitral regurgitation and/or altered ring geometries. Findings will be quantitatively compared to the forces known to cause suture failure and tissue tearing. Collectively, these investigations will elucidate the mechanisms of ring dehiscence and inform next-generation ring designs.

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