Author ORCID Identifier

https://orcid.org/0000-0003-0057-1877

Year of Publication

2021

Degree Name

Master of Science in Mechanical Engineering (MSME)

Document Type

Master's Thesis

College

Engineering

Department/School/Program

Mechanical Engineering

First Advisor

Dr. Jonathan F. Wenk

Second Advisor

Dr. Kenneth S. Campbell

Abstract

Myofiber organization in the heart plays an important role in achieving and maintaining physiological cardiac function. In many cardiac disease states, myofibers and particularly cardiomyocytes are disorganized in chaotic patterns, a phenotype known broadly as myocardial disarray. In familial hypertrophic cardiomyopathy (HCM), this disorganization in the form of myocyte disarray is thought to contribute to impaired cardiac function and the development of arrhythmia during disease progression. However, the mechanisms regarding fiber reorientation in the heart are yet still unclear, and few adaptative laws have been created to explore these mechanisms. A stretch-based law was developed with the aim of achieving physiological fiber organization from a non-physiological starting point, but it was not sufficient to reproduce the normal human architecture. Adaptation under pathological conditions was not attempted.

We hypothesize that reorientation occurs in cardiac tissue such that shear stresses are minimized and that this mechanism, in tandem with local mechanical heterogeneities caused by certain disease states, is responsible for the development of disarray. The aim of this work was to propose a novel stress-based fiber reorientation law and assess its potential to induce myocardial disarray in a computational model of the heart. The law was implemented in a finite element framework with simple mesh geometries and tested against known mechanics solutions. Then, heterogeneities in passive and contractile properties among mesh elements was introduced, and the fiber orientations adapted under cyclical loading conditions were evaluated. Stress-based reorientation produced well-organized orientations for homogeneous structures and fiber disorganization for structures with heterogeneous passive or contractile properties. We conclude that the stress-based reorientation law proposed in this work can potentially characterize fiber adaptation in the heart and could be used to develop myocardial disarray in a cardiac model. Further work includes the implementation of the reorientation law in a left ventricle model and the validation of results with experimental studies.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.348

Funding Information

This study was supported by the National Institutes of Health grant 3U01HL133359-03S1 from 2019-2021.

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