Mechanical Stimuli for Left Ventricular Growth During Pressure Overload

Background The mechanical stimulus (i.e., stress or stretch) for growth occurring in the pressure-overloaded left ventricle (LV) is not exactly known. Objective To address this issue, we investigate the correlation between local ventricular growth (indexed by local wall thickness) and the local acute changes in mechanical stimuli after aortic banding. Methods LV geometric data were extracted from 3D echo measurements at baseline and 2 weeks in the aortic banding swine model ( n = 4). We developed and calibrated animal-specific finite element (FE) model of LV mechanics against pressure and volume waveforms measured at baseline. After simulation of the acute effects of pressure-overload, the local changes of maximum, mean and minimum myocardial stretches and stresses in three orthogonal material directions (i.e., fiber, sheet and sheet-normal) over a cardiac cycle were quantified. Correlation between mechanical quantities and the corresponding measured local changes in wall thickness was quantified using the Pearson correlation number (PCN) and Spearman rank correlation number (SCN). Results At 2 weeks after banding, the average septum thickness decreased from 10.6 ± 2.92 mm to 9.49 ± 2.02 mm, whereas the LV free-wall thickness increased from 8.69 ± 1.64 mm to 9.4 ± 1.22 mm. The FE results show strong correlation of growth with the changes in maximum fiber stress (PCN = 0.5471, SCN = 0.5111) and changes in the mean sheet-normal stress (PCN = 0.5266, SCN = 0.5256). Myocardial stretches, however, do not have good correlation with growth. Conclusion These results suggest that fiber stress is the mechanical stimuli for LV growth in pressure-overload.