Non‐uniform transmural remodeling in ovine chronic mitral regurgitation

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 (E C ) and radial (E R ) 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 E C was greater in ENDO than EPI (0.09±0.12 vs. 0.02±0.07, P<0.05) and HOLE E C in ENDO was greater than CNTL E C in ENDO (0.09±0.12 vs. −0.01±0.06, P<0.05). E R 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: E C and E R 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).