Transmural Strains in the Ovine Left Ventricular Lateral Wall During Diastolic Filling

Rapid early diastolic left ventricular (LV) filling requires a highly compliant chamber immediately after systole, allowing inflow at low driving pressures. The transmural LV deformations associated with such filling are not completely understood. We sought to characterize regional transmural LV strains during diastole, with focus on early filling, in ovine hearts at 1 week and 8 weeks after myocardial marker implantation. In seven normal sheep hearts, 13 radiopaque markers were inserted to silhouette the LV chamber and a transmural beadset was implanted into the lateral equatorial LV wall to measure transmural strains. Four-dimensional marker dynamics were obtained 1 week and 8 weeks thereafter with biplane videofluoroscopy in closed-chest, anesthetized animals. LV transmural strains in both cardiac and fiber-sheet coordinates were studied from filling onset to the end of early filling (EOEF, 100 ms after filling onset) and at end diastole. At the 8 week study, subepicardial circumferential strain $(ECC)$ had reached its final value already at EOEF, while longitudinal and radial strains were nearly zero at this time. Subepicardial $ECC$ and fiber relengthening $(Eff)$ at EOEF were reduced to 1 compared with 8 weeks after surgery (⁠$ECC:0.02±0.01$ to $0.08±0.02$ and $Eff:0.00±0.01$ to $0.03±0.01$⁠, respectively, both $P<0.05$⁠). Subepicardial $ECC$ during early LV filling was associated primarily with fiber-normal and sheet-normal shears at the 1 week study, but to all three fiber-sheet shears and fiber relengthening at the 8 week study. These changes in LV subepicardial mechanics provide a possible mechanistic basis for regional myocardial lusitropic function, and may add to our understanding of LV myocardial diastolic dysfunction.