Mitral Annular Size Predicts Alfieri Stitch Tension in Mitral Edge-to-Edge Repair

Tomasz A. Timek1,6, Sten L. Nielsen4, David T. Lai1, Frederick Tibayan1, David Liang2, George T. Daughters1,5, Philip Beineke3, Trevor Hastie3, Neil B. Ingels, Jr.1,5, D. Craig Miller1
1Department of Cardiothoracic Surgery, 2Division of Cardiovascular Medicine, 3Department of Biostatistics, Stanford University School of Medicine, Stanford, CA, USA, 4Department of Cardiothoracic and Vascular Surgery, Aarhus University, Aarhus, Denmark, 5Laboratory of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation, Palo Alto, CA, USA
6Present address: Department of Surgery, Loma Linda University Medical Center, Loma Linda, CA, USA
 

Background and aim of the study: Whilst increased ‘Alfieri stitch’ tension may reduce the durability of ‘edge-to-edge’ mitral repair, the factors affecting suture tension are unknown. In order to study hemodynamics and left ventricular (LV) and annular dynamics that determine suture tension, the central edge of the mitral leaflets was approximated with a miniature force transducer to measure leaflet tension (T) at the leaflet approximation point.
Methods: Eight sheep were studied under open-chest conditions immediately after surgical placement of a force transducer and implantation of radiopaque markers on the left ventricle and mitral annulus (MA). Hemodynamic variables were altered by two caval occlusion steps (DV1 and DV2) and dobutamine infusion. Three-dimensional marker coordinates were obtained by simultaneous biplane videofluoroscopy to measure LV volume, MA area (MAA) and septal-lateral (SL) annular dimension throughout the cardiac cycle.
Results: At baseline, peak Alfieri stitch tension (0.30 ± 0.18 N) was observed 96 ± 61 ms prior to end-diastole

coincident with peak annular SL diameter (98 ± 58 ms before end-diastole). Dobutamine infusion decreased suture tension (from 0.30 ± 0.18 N to 0.20 ± 0.12 N, p = 0.01), although peak systolic pressure increased significantly (138 ± 19 versus 115 ± 14 mmHg; p = 0.03). A regression model was fitted with the goal of interpreting the hemodynamic and geometric predictors of tension as their influence varied with time: Tt (N) = 0.1916 + 0.2115 ¥ SL (cm) - 0.1996 ¥ MAA/SL (cm2/cm) + ft ¥ LVP (mmHg), where Tt is tension at any time during the cardiac cycle and ft is the time-varying coefficient of LVP.
Conclusion: Tension on the leaflets in the edge-to-edge repair is determined primarily by MA SL size, and paradoxically is lower when the contractile state is enhanced. This indicates that annular and/or LV dilatation increase stitch tension and may adversely affect durability of the repair if concomitant ring annuloplasty is not performed.
 
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