18. EFFECTS OF MYOCYTE HETEROGENEITY ON VENTRICULAR FUNCTION: A MULTI-SCALE MODELING STUDY

Department: Bioengineering
Faculty Advisor(s): Andrew McCulloch

Primary Student
Name: Stuart Gaylon Campbell
Email: sgcampbe@ucsd.edu
Phone: 858-534-6616
Grad Year: 2009

Abstract
Cardiac muscle cells isolated from the left-ventricular (LV) wall exhibit region-dependent behavior. Those isolated from the outer third of the wall (epicardium) contract and relax more rapidly than myocytes found in the inner region of the wall (endocardium). These differences in contraction dynamics have unknown effects on the regional and global function of the LV. We have created a three-dimensional, multi-scale model of LV function which simultaneously solves equations describing electrical propagation, finite tissue deformation, muscle contraction, and ventricular loading. This model enabled prediction of LV pump function and regional strains under two conditions: 1) with cell-level parameters assigned in a physiologic manner, spatially arranged in layers through the LV wall (BASELINE), and 2) with cell-level parameters assigned in a randomized fashion (RANDOM). The two simulations produced identical stroke volumes and peak LV pressures. Strains at end-ejection were also nearly identical in the two simulations. The greatest differences were evident during early ejection, where BASELINE produced a larger range of fiber strains as measured across the LV wall in comparison with the RANDOM simulation. We conclude that the principal effect of myocyte heterogeneity in the LV is on fiber strains during early systole. We also conclude that global LV pump function is not sensitive to the observed spatial patterns of myocyte behavior.

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