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    What forces act on a flat rigid mitral annuloplasty ring? Jensen Morten Ø,Jensen Henrik,Nielsen Sten L,Smerup Morten,Johansen Peter,Yoganathan Ajit P,Nygaard Hans,Hasenkam J Michael The Journal of heart valve disease 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.
    Strength comparison of mitral annuloplasty ring and suturing combinations: an in-vitro study. Spratt John R,Spratt John A,Beachley Vince,Kang Qian The Journal of heart valve disease BACKGROUND AND AIM OF THE STUDY:While mattress sutures are commonly used to secure annuloplasty rings during mitral valve repair, the use of a flexible ring secured with a running polypropylene suture has recently been advocated. The study aim was to assess the separation tensions of semi-rigid and flexible rings using mattress and running suture techniques in an in-vitro static load model. METHODS:Semi-rigid and flexible annuloplasty rings were sutured with either mattress or running sutures (RM, RR, FM, FR) in four groups, of eight hearts each. Twelve additional sutures were passed through the surfaces of each ring to fix the preparation to a testing machine. In a fifth (control) group the mattress sutures securing a flexible ring (FMS) were connected directly to the machine. Each preparation was subjected to progressive axially directed (base-apex) tension until ring-tissue separation occurred. RESULTS:The first major decrease in tension (defined as > or = 10 N in < or = 1.5 s) typically occurred with the separation of at least three adjacent sutures. These starting tensions (N) were: FMS 117 +/- 32.6, RR 131.7 +/- 30.5, RM 137.4 +/- 35.3, FM 152.1 +/- 32.3, and FR 213.2 +/- 30.5. The magnitudes of tension decrease with separation (and percentage of starting tensions) were: FMS 25.4 (21.2%), RR 26.8 (17.6%), RM 28.9 (21.6%), FM 24.6 (17.6%), and FR 22.5 (10.8%). The FR group required more tension to separate than the other groups (p < 0.001), but had a lower magnitude of force drop at dehiscence. CONCLUSION:Flexible rings secured with a running suture required more force to separate than other ring-suture combinations. The lower magnitude of force drop in this group indicated a better tension distribution than in the other groups. Semi-rigid rings separated with a lower force, and had larger drops in tension, regardless of the suture technique used.
    In-Vivo Evaluation of Flexible Mitral Annuloplasty Rings: Are They All the Same? Rasmussen Jonas,Nielsen Skov Søren,Ropcke Diana M,Juan Tjoernild Marcell,Ilkjaer Christine,Lyager Nielsen Sten The Journal of heart valve disease BACKGROUND:Currently, several different flexible mitral annuloplasty rings are available, and their efficacy for surgical repair of the mitral valve is, in general, considered equal. However, clinical experience indicates differences in remodeling capacity that have not yet been quantitatively assessed. The study aim was to compare the biomechanical properties of two commonly used flexible mitral annuloplasty rings in an acute pig model. METHODS:Medtronic Simulus Flex (n = 5) and Medtronic Duran AnCore (n = 7) flexible mitral annuloplasty rings were implanted in pigs (bodyweight 80 kg). The native mitral valve was used as a reference (n = 7). Mitral annular dynamics and dimensions were assessed using 11 sonomicrometry crystals placed in the mitral apparatus. A dedicated force transducer was used to detect deformational force transmission between the annuloplasty ring and the mitral annulus. RESULTS:Cyclic changes in mitral annular circumference and commissure-commissure distance were significantly reduced in the Simulus Flex group compared to the Duran AnCore group (p = 0.025 and p <0.01, respectively). In the Simulus Flex group, smaller deformational forces were recorded compared to the Duran AnCore group, but the difference was not statistically significant (p = 0.52 and p = 0.06 for the septal-lateral and the commissure-commissure force measurements, respectively). CONCLUSIONS:The Simulus Flex ring showed significantly more remodeling capacity than the Duran AnCore ring, but the latter ring preserved the natural dynamics of the mitral valve to a greater degree. Insights into these biomechanical differences may facilitate strategies for surgical reconstruction in degenerative mitral valve disease, especially in patients with excessive amounts of tissue and who are at risk of systolic anterior motion of the mitral valve.
    Suture forces in undersized mitral annuloplasty: novel device and measurements. Siefert Andrew W,Pierce Eric L,Lee Madonna,Jensen Morten Ø,Aoki Chikashi,Takebayashi Satoshi,Fernandez Esmerats Joan,Gorman Robert C,Gorman Joseph H,Yoganathan Ajit P The Annals of thoracic surgery 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. 10.1016/j.athoracsur.2014.02.036