Transmural LV Systolic Wall Thickening Gradients and Models of Heart Wall Mechanics

We implanted arrays of radiopaque markers to measure lateral equatorial wall transmural strains and global and regional LV geometry in 7 sheep. Without intervening procedures, one and eight weeks after surgery, 4-D datasets from stereo radiographic studies were processed to yield transmural strains from each heart. In accordance with previous theoretical predictions and experimental results, we hypothesized that systolic radial strain (i.e., wall thickening) would exhibit a transmural gradient, increasing from subepicardium to subendocardium, and, as previous work suggested that this was a fundamental mechanism, this gradient would be observed at both the one- and eight-week studies. The one-week studies yielded the expected gradient. This gradient, however, was not present in the eight-week studies, although LV shape and hemodynamics were virtually identical to their one-week values. We discuss the implications of these findings to mechanistic theories of heart wall mechanics.