Effect of chronotropy and inotropy on stitch tension in the edge-to-edge mitral repair

Our prior studies suggest that mitral annular septal-lateral (SL) diameter is the chief determinant of "Alfieri stitch" tension, but hemodynamic parameters may also play a role. We approximated the central edge of the mitral leaflets with a miniature force transducer to measure tension (T) at the leaflet approximation point during inotropic and chronotropic stimulation. Eight sheep were studied under open-chest conditions immediately after surgical placement of a miniature force transducer to approximate the leaflets and implantation of radiopaque markers on the LV and mitral annulus (MA). Chronotropic stimulation was induced with atrial pacing at 130 minutes(-1) (n=5) whereas inotropic state was increased with i.v. CaCl2 bolus (n=8). Hemodynamic data, stitch tension, and 3-D marker coordinates were obtained throughout the cardiac cycle before and during each intervention. Peak stitch tension (T(MAX)) under all conditions was observed in diastole and temporally correlated with peak annular SL (SL(MAX)) size. Atrial pacing did not change peak transducer tension or annular size. Calcium infusion also did not alter peak transducer tension (0.29+/-0.11 versus 0.32+/-0.10 N; P=NS) and only slightly reduced SL dimension (29.9+/-3.3 versus 29.3+/-3.5 mm; P