Effect of Cutting
Second-Order Chordae on In-Vivo Anterior Mitral Leaflet Compound Curvature
Filiberto Rodriguez, Frank Langer, Katherine B. Harrington,
Frederick A. Tibayan, Mary K. Zasio, David Liang, George T. Daughters,
Neil B. Ingels, D. Craig Miller
Department of Cardiothoracic Surgery and Division
of Cardiovascular Medicine, Stanford University School of Medicine, Stanford,
CA, Laboratory of Cardiovascular Physiology and Biophysics, Palo Alto
Medical Foundation Research Institute, Palo Alto, CA, USA |
Background and aim of the study: Leaflet curvature
determines leaflet stress. In order to assess the influence of second-order
chordae (2°CT) on anterior mitral valve leaflet (AMVL) geometry,
AMVL curvature was measured before (Baseline) and after (CUT) cutting
the 2°CT.
Methods: Miniature radiopaque markers were sutured onto
the AMVL in eight sheep: four along the central-meridian from mid-septal
annulus to the free-margin; and one each at the 2°CT insertion.
Biplane videofluoroscopic data were acquired (open-chest) before
and after CUT. Marker-triplet 3-D coordinates were used to calculate
radii-of-curvature at LVPmax along the central-meridian (ROCm)
and across the AMVL belly (commissure-commissure axis, ROCc-c).
Results: CUT did not change LVPmax (111 ± 12 versus
106
± 11 mmHg; p = 0.19). At baseline, the AMVL central-meridian had
compound curvature: Convex to the left ventricle near the annulus (-ROCm)
and concave near the free-margin (+ROCm). After CUT, the AMVL flattened:
ROCm increased near the annulus (from -1.37 ± 0.52 to -12.58 ±
29.04 cm; p = 0.02), but did not change near the edge. In the |
commissure-commissure axis, ROCc-c was concave to the
left ventricle at baseline and increased after CUT in all eight animals.
In five sheep, ROCc-c was increased (from 1.93 ± 1.01 to 2.80 ± 1.36
cm; p = 0.03), but in three sheep ROCc-c was increased and inverted (from
3.65 ± 2.17 to -1.72 ± 0.53 cm; p = 0.03), becoming convex
to the left ventricle.
Conclusion: Compound curvature along the AMVL central-meridian
appears to be an intrinsic leaflet property that persists even
without support from second-order chordae, whereas concave curvature
in the commissure-commissure axis is more dependent on intact second-order
chordae. Leaflet compound curvature must be incorporated into future
finite element models to characterize leaflet stresses accurately.
The importance of second-order chordae in maintaining leaflet shape
must be considered during mitral repair. A larger ROC increases
leaflet stresses, while reversal of ROC changes tensile stress
to compressive stress; this might trigger deleterious leaflet remodeling
after chordal cutting.
The Journal of Heart Valve Disease 2005;14:592-602 |