Regional Gradients in Tissue Anisotropy During Pressure Overload Hypertrophy in the Rat Left Ventricle

Many studies have shown that the structural composition of the normal heart is spatially non‐uniform. We hypothesized that due to spatial differences in tissue structure and function, hypertrophic growth occurs non‐uniformly, especially in moderate hypertrophy. Using high resolution, high fidelity diffusion tensor magnetic resonance imaging (DT‐MRI), we calculated and compared fractional anisotropy (FA) in several regions of aortic banded and sham hearts. Preliminary results indicate that the FA is decreased uniformly in severe hypertrophy (mean 0.16) compared to sham controls (mean 0.22). A decrease in FA is consistent with known changes in myocyte shape during concentric hypertrophy, wherein cell width increases more than cell length. In mild‐moderate hypertrophy, the mean FA across the entire LV (0.21) was comprised of two subpopulations with mean FA 0.11 and 0.23. The subpopulation with lower FA was isolated to the subendocardium, whereas the higher FA values were localized in the mid‐and subepicardium. We conclude that hypertrophic growth occurs either earlier, with higher sensitivity, or both in the subendocardium, and we propose that endogenous spatial differences in cell and tissue structure (and therefore function) lead to this variation in hypertrophic growth. Support or Funding Information NIH/NHLBI Training Grant #2015‐0453NIH/NIGMS #P50 GM094503‐04