Mitral annular hinge motion contribution to changes in mitral septal–lateral dimension and annular area

Objective

The mitral annulus is a dynamic, saddle-shaped structure consisting of fibrous and muscular regions. Normal physiologic mechanisms of annular motion are incompletely understood, and more complete characterization is needed to provide rational basis for annuloplasty ring design and to enhance clinical outcomes.

Methods

Seventeen sheep had radiopaque markers implanted; 16 around the annulus and 2 on middle anterior and posterior leaflet edges. Four-dimensional marker coordinates were acquired with biplanar videofluoroscopy at 60 Hz. Hinge angle was quantified between fibrous and muscular annular planes, with 0° defined at end diastole, to characterize its contribution to alterations in mitral septal–lateral dimension and 2-dimensional total annular area throughout the cardiac cycle.

Results

During isovolumic contraction (pre-ejection), hinge angle abruptly increased, reaching maximum (steepest saddle shape, change 18° ± 13°) at peak left ventricular pressure. During ejection, hinge angle did not change; it then decreased during early filling (change 2° ± 2°). Septal–lateral dimension and total area paralleled hinge angle dynamics and leaflet distance (anterior to posterior marker). Pre-ejection septal–lateral reduction was 13% ± 7% (3.3 ± 1.5 mm) from 9% muscular dimension fall and 18° ± 13° hinge angle increase.

Conclusions

Pre-ejection increase in hinge angle contributes substantially to septal–lateral and total area reduction, facilitating leaflet coaptation. Semirigid annuloplasty rings or partial bands may preserve hinge motion, but possible recurrent annular dilatation could result in recurrent mitral regurgitation. Long-term clinical studies are required to determine who might benefit most from preserving intrinsic hinge motion without compromising repair durability.

CTSNet classification: 35

Abbreviations and Acronyms: ▵Ф, change in mitral annular hinge angle, Ф, mitral annular hinge angle, 2D, 2-dimensional, 2DFA, 2-dimensional fibrous annular area, 2DMA, 2-dimensional muscular annular area, 2DROC_xy, 2-dimensional radius of curvature on xy plane, 2DTA, 2-dimensional total mitral annular area, 3D, 3-dimensional, 3DFA, 3D fibrous annular area, 3DMA, 3D muscular annular area, 3DTA, 3-dimensional total mitral annular area, AH, annular height, AoP, aortic pressure, C-C, commissure to commissure, E_A-E_P, leaflet edge marker distance, ED, end diastole, ES, end systole, H-L, hinge axis to midlateral, H-S, hinge axis to saddle-horn, IVC, isovolumic contraction, IVR, isovolumic relaxation, LA, left atrium, LV, left ventricle, LVP, left ventricular pressure, S-L, septal (saddle-horn) to lateral (midlateral annulus)