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(Circulation. 2007;116:I-276 – I-281.)
© 2007 American Heart Association, Inc.

Surgery for Valvular Heart Disease

Effect of Chronotropy and Inotropy on Stitch Tension in the Edge-to-Edge Mitral Repair

Tomasz A. Timek, MD; Sten L. Nielsen, MD; David T. Lai, FRACS; David Liang, MD, PhD; George T. Daughters, MS; Neil B. Ingels, Jr, PhD; D. Craig Miller, MD

From the Department of Cardiothoracic Surgery (T.A.T., D.T.L., G.T.D., N.B.I., D.C.M.) and the Division of Cardiovascular Medicine (D.L.), Stanford University School of Medicine, Stanford, Calif; the Department of Cardiothoracic and Vascular Surgery (S.L.N.), Aarhus University, Aarhus, Denmark; and the Laboratory of Cardiovascular Physiology and Biophysics (G.T.D., N.B.I.), Research Institute of the Palo Alto Medical Foundation, Palo Alto, Calif.

Correspondence to D. Craig Miller, MD, Department of Cardiothoracic Surgery, Falk Cardiovascular Research Center, Stanford University School of Medicine, Stanford, California 94305-5247. E-mail dcm{at}stanford.edu

Background— 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.

Methods and Results— 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 IV 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<0.05).

Conclusion— Isolated increase in heart rate or inotropic state did not alter peak stitch tension whereas enhanced contractile state decreased SL diameter minimally. These data, combined with those from our previous study, suggest that geometric (SL diameter) rather than hemodynamic parameters are the main determinants of "Alfieri stitch" tension. This implies that any interventional or surgical edge-to-edge repair performed without concomitant annular reduction to limit the SL dimension could expose the leaflet junction to forces which could limit repair durability.

Key Words: mitral valve • valvuloplasty • valves