Characteristic Strain Pattern of Moderately Ischemic Myocardium Investigated in a Finite Element Simulation Model

摘要

Background: Myocardial ischemia in the left ventricular (LV) myocardium introduces non-uniform and pathological strain patterns. Total passive segments lengthen when pressure increases during early systole and shorten when pressure drops at the end of ejection. Moderately ischemic segments typically lengthen during isovolumic contraction, start shortening during ejection and continue shortening, usually at an increased rate, after aortic valve closure. Aim: The aim of this study was to investigate possible mechanisms for the characteristic strain patterns in moderately ischemic regions using a simulation model of the LV wall. Methods: A thick-walled truncated ellipsoidal finite element model was used to represent the LV geometry. The model included mathematical descriptions of fiber orientation, passive elastic properties, and actively generated fiber stress. A severely ischemic region and a moderately ischemic border zone were incorporated in the model. The severely ischemic region was made stiffer and generated no active fiber stress during systole. The border zone was made slightly stiffer, active fiber stress was reduced and generated at a slower rate while the relaxation rate was slower than in the normal regions. The cardiac cycle was simulated by applying physiological pressure-volume boundary conditions. Results: The strain pattern in the severely ischemic region resembled the pressure curve with lengthening during pressure rise and shortening during pressure decrease, while the border zone started shortening after an initial early systolic lengthening and continued shortening during isovolumic relaxation at an increased rate. Conclusion: The characteristic moderately ischemic strain pattern may be caused by slower mechanical activation and relaxation rates.