Persistent Shift in Laminar Planes Contribute to Post-Surgical Decline in LVEF in Patients with Primary Mitral Regurgitation
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Background
The double helical direction of LV laminar sheets from endocardium to epicardium allows for wringing motion or LV twist. This provides a major component to LV wall thickening, stroke volume, and ejection fraction (EF). When this laminar sheet arrangement changes in Primary Mitral Regurgitation (PMR) and whether it reverts to normal after mitral valve repair is unknown.
Methods
Normal subjects (n=55) PMR patients had cardiac magnetic resonance imaging (CMR) with tissue tagging and 3-dimensional (3-D) analysis. They were grouped as asymptomatic moderate (n=23) and severe PMR (n=25) by regurgitant volume (RV) and pre-surgery (n=54) with post-surgery follow up at six, 12, and 24 months. Amplitude and directional vector of longitudinal (Ell), circumferential (Ecc), and maximal shortening were computed along with principle strain angles (Ecc°, Ell°, and Err°) at basal, mid, and distal LV levels.
Results
Asymptomatic moderate (RV 35 ± 16 ml; LVEF 62 ± 6%) and severe (RV 55 ±16 ml; LVEF 63 ± 6%) and symptomatic pre-surgery (RV 61 ± 29 ml; LVEF 63 ± 8%) had similar increases in mid LV 3-D radius to wall thickness (R/T), decrease in LV mass to volume (M/V) and sphericity index (SI) vs. normal. Radial longitudinal shear strain and mid LV Ecc° and EII° angles increased in all PMR groups, consistent with a shift in LV laminar plane direction and decreased LV SI. Post-surgery, LV end-diastolic (ED) volume, LVED M/V and 3-D R/T returned to normal within two years; however, mid LV circumferential, longitudinal, and maximal shortening decrease below normal. LV Ecc° and Ell° angles, and SI are unchanged from pre-surgery. LVEF decreased post-surgery and had a negative correlation with LV twist at six (r 2 = 0.30, p < 0.001), 12, (r 2 = 0.33, p < 0.001) and 24 months (r 2 = 0.38, p < 0.001) post-surgery.
Conclusion
Early changes in Ecc° and Ell° angles, radial longitudinal shear strain, and LV spherical dilatation are consistent with a shift of LV laminar planes that persists after surgery. The extent to which this affects LV twist may underlie a heretofore explanation underlying the decrease in LVEF after surgery for PMR.
