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(Circulation. 2004;110:II-115 – II-122.)
© 2004 American Heart Association, Inc.

Surgery for Valvular Heart Disease

Importance of Mitral Valve Second-Order Chordae for Left Ventricular Geometry, Wall Thickening Mechanics, and Global Systolic Function

Filiberto Rodriguez, MD; Frank Langer, MD; Katherine B. Harrington, BA; Frederick A. Tibayan, MD; Mary K. Zasio, BA; Allen Cheng, MD; David Liang, MD PhD; George T. Daughters, MS; James W. Covell, MD; John C. Criscione, MD PhD; Neil B. Ingels, PhD; D. Craig Miller, MD

From the Department of Cardiothoracic Surgery (F.R., F.L., K.B.H., F.A.T., M.K.Z., A.C., G.T.D., N.B.I., C.M.) and Division of Cardiovascular Medicine (D.L.), Stanford University School of Medicine, Stanford, Calif; Department of Medicine (J.W.C.), University of California San Diego, La Jolla, Calif; Department of Biomedical Engineering (J.C.C.), Texas A&M University, College Station, Tex; Laboratory of Cardiovascular Physiology and Biophysics (G.T.D., N.B.I.), Palo Alto Medical Foundation Research Institute, Palo Alto, Calif.

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

Background— Mitral valvular–ventricular continuity is important for left ventricular (LV) systolic function, but the specific contributions of the anterior leaflet second-order "strut" chordae are unknown.

Methods and Results— Eight sheep had radiopaque markers implanted to silhouette the LV, annulus, and papillary muscles (PMs); 3 transmural bead columns were inserted into the mid-lateral wall between the PMs. The strut chordae were encircled with exteriorized wire snares. Three-dimensional marker images and hemodynamic data were acquired before and after chordal cutting. Preload recruitable stroke work (PRSW) and end-systolic elastance (E_es) were calculated to assess global LV systolic function (n=7). Transmural strains were measured from bead displacements (n=4). Chordal cutting caused global LV dysfunction: E_es (1.48±1.12 versus 0.98±1.30 mm Hg/mL, P=0.04) and PRSW (69±16 versus 60±15 mm Hg, P=0.03) decreased. Although heart rate and time from ED to ES were unchanged, time of mid-ejection was delayed (125±18 versus 136±19 ms, P=0.01). Globally, the LV apex and posterior PM tip were displaced away from the fibrous annulus and LV base-apex length increased at end-diastole and end-systole (all +1 mm, P<0.05). Locally, subendocardial end-diastolic strains occurred: Longitudinal strain (E₂₂) 0.030±0.013 and radial thickening (E₃₃) 0.081±0.041 (both P<0.05 versus zero). Subendocardial systolic shear strains were also perturbed: Circumferential-longitudinal "micro-torsion" (E₁₂) (0.099±0.035 versus 0.075±0.025) and circumferential radial shear (E₁₃) (0.084±0.023 versus 0.039±0.008, both P<0.05).

Conclusion— Cutting second-order chords altered LV geometry, remodeled the myocardium between the PMs, perturbed local systolic strain patterns affecting micro-torsion and wall-thickening, and caused global systolic dysfunction, demonstrating the importance of these chordae for LV structure and function.

Key Words: contractility • mechanics • mitral valve • regurgitation • structure