Importance of mitral valve second-order chordae for left ventricular geometry, wall thickening mechanics, and global systolic function.
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.


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).


CONCLUSIONS
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.
Rodriguez
Filiberto
F
Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, Calif 94305-5247, USA.
Langer
Frank
F
Harrington
Katherine B
KB
Tibayan
Frederick A
FA
Zasio
Mary K
MK
Cheng
Allen
A
Liang
David
D
Daughters
George T
GT
Covell
James W
JW
Criscione
John C
JC
Ingels
Neil B
NB
Miller
D Craig
DC
D000818:Animals; D001696:Biomechanical Phenomena; D002815:Chordae Tendineae / Q000502:physiology* / Q000601:surgery; D006339:Heart Rate; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000648:ultrastructure*; D006439:Hemodynamics; D021621:Imaging, Three-Dimensional; D008943:Mitral Valve / Q000000981:diagnostic imaging / Q000648:ultrastructure*; D011859:Radiography; D012756:Sheep; D013314:Stress, Mechanical; D013599:Systole / Q000502:physiology*; D014102:Torsion Abnormality; D018487:Ventricular Dysfunction, Left / Q000209:etiology / Q000503:physiopathology; D016277:Ventricular Function, Left / Q000502:physiology*