Non‐uniform transmural remodeling in ovine chronic mitral regurgitation

Abstract

Objective:Test the hypothesis that chronic “pure” mitral regurgitation (MR) induces non‐uniform transmural LV remodeling.Methods:Surgical creation of a ∼4.8mm hole in the posterior mitral leaflet created “pure” MR in 12 sheep (HOLE); 8 were sham operated (CNTL). Radiopaque transmural beads in the anterobasal wall were used to quantify epicardial (EPI) and endocardial (ENDO) remodeling strains in the circumferential (EC) and radial (ER) directions. Remodeling strains were calculated using end‐diastole (ED) 1 week (WK‐01) postoperatively as the reference and ED at 12 weeks (WK‐12) as the deformed configuration.Results:MR grade was greater in HOLE (∼3) than CNTL (<1) (P<0.001) at WK‐01 and WK‐12. LVED volume index increased in HOLE from WK‐01 to WK‐12 (P<0.05) and LV mass index was greater in HOLE at WK‐12 (P<0.01). HOLE EC was greater in ENDO than EPI (0.09±0.12 vs. 0.02±0.07, P<0.05) and HOLE EC in ENDO was greater than CNTL EC in ENDO (0.09±0.12 vs. −0.01±0.06, P<0.05). ER was less in EPI than ENDO for HOLE (−0.23±0.13 vs. −0.04±0.23, P<0.05) and CNTL (−0.15±0.07 vs. 0.15±0.44, P<0.05).Conclusion:EC and ER remodeling strains demonstrated significant transmural non‐uniformity. This non‐uniformity may arise from transmural differences in tissue stress. Such a transmural imbalance may underlie the decrease in LV torsion associated with chronic MR.Support:NIH HL29589/HL67025 (DCM) and HL087614 (DBE).