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| Effects of Annuloplasty Ring Implantation on Regional Mitral Leaflet Tenting Area During Acute Myocardial Ischemia |
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Wolfgang Bothe1, Elizabeth H. Stephens1, John-Peder E. Kvitting1, Julia C. Swanson1, Neil B. Ingels2, D. Craig Miller1 1 Cardiothoracic Surgery, Stanford School of Medicine, Stanford, CA; 2 Laboratory of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation, Mountain View, CA Objective: Preoperative tenting area (TA) is a predictive factor for recurrent mitral regurgitation (MR) in patients with ischemic MR undergoing annuloplasty. TA decreases with ring implantation, but may increase after surgery and be associated with recurrent MR. Insights into regional alterations in TA before and after ring implantation could improve our understanding of mechanisms leading to ischemic MR and recurrent MR after annuloplasty. We quantified regional changes in mitral leaflet TA during acute myocardial ischemia in an ovine model with and without an annuloplasty ring. Methods: 14 radiopaque markers were implanted in 7 adult sheep: one to the mitral annular saddle horn (MASH), 4 to the central septal-lateral (S-L) meridian of the anterior mitral leaflet (AML), 4 to the commissure-commissure (C-C) meridian of the AML, 2 to the central S-L meridian of the posterior leaflet (PML), one to the mid-lateral mitral annulus (MAML) and one each to the anterior and posterior commissures (ACOM, PCOM). True-sized CE Physio annuloplasty rings were inserted in a releasable fashion. Under acute open-chest conditions, marker coordinates were obtained using biplane videofluoroscopy (60Hz) with ring inserted at baseline (BL+RING) and after 90s of LCx occlusion (ISCH+RING). After ring release, another dataset was acquired at baseline (BL) and after 90s of LCx occlusion (ISCH). Proximal (Area 1), distal (Area 2), total (Area 1+2) AML S-L TA, AML C-C TA (Area 3) and PML S-L TA were computed at mid-systole from sums of marker triangles with the midpoint between MASH and MAML being the vertex for the S-L TA triangles and the midpoint between ACOM and PCOM the vertex for the AML C-C TA triangles (Fig. A). Results: Fig. B: Compared to BL, MR grade and all measured TAs significantly increased with ISCH. Relative to BL+RING, the AML S-L TAs (Area 1, Area 2, Area 1+2) and MR grade did not change in ISCH+RING; surprisingly, however, AML C-C TA and PML S-L TA both increased. Conclusion: Ring implantation prevented acute ischemic MR despite the presence of significant commissural AML and S-L PML tenting, most likely due to minimizing AML S-L tenting. Assuming the results from our acute experimental ischemic preparation hold true in patients with chronic IMR, disease-specific annuloplasty rings should aim primarily to reduce the mitral annular S-L dimension. Our new observation suggests that normalizing C-C tethering, e.g., via new ring designs or subvalvular approaches, may also help to optimize long-term outcomes. 
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