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Technical Briefs

Regional Left Ventricular Myocardial Contractility and Stress in a Finite Element Model of Posterobasal Myocardial Infarction

[+] Author and Article Information
Jonathan F. Wenk1

Department of Surgery, and Department of Bioengineering, University of California, San Francisco, CA 94121; Department of Veterans Affairs Medical Center, San Francisco, CA 94121jwenk1@me.berkeley.edu

Kay Sun, Zhihong Zhang, Mehrdad Soleimani

Department of Surgery, University of California, San Francisco, CA 94121; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

Liang Ge, Mark B. Ratcliffe, Julius M. Guccione

Department of Surgery, and Department of Bioengineering, University of California, San Francisco, CA 94121; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

David Saloner

Department of Radiology, University of California, San Francisco, CA 94121; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

Arthur W. Wallace

Department of Anesthesia, University of California, San Francisco, CA 94121; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

1

Corresponding author.

J Biomech Eng 133(4), 044501 (Feb 17, 2011) (6 pages) doi:10.1115/1.4003438 History: Received September 07, 2010; Revised January 07, 2011; Posted January 14, 2011; Published February 17, 2011; Online February 17, 2011

Recently, a noninvasive method for determining regional myocardial contractility, using an animal-specific finite element (FE) model-based optimization, was developed to study a sheep with anteroapical infarction (Sun, 2009, “A Computationally Efficient Formal Optimization of Regional Myocardial Contractility in a Sheep With Left Ventricular Aneurysm,” ASME J. Biomech. Eng., 131(11), p. 111001). Using the methodology developed in the previous study (Sun, 2009, “A Computationally Efficient Formal Optimization of Regional Myocardial Contractility in a Sheep With Left Ventricular Aneurysm,” ASME J. Biomech. Eng., 131(11), p. 111001), which incorporates tagged magnetic resonance images, three-dimensional myocardial strains, left ventricular (LV) volumes, and LV cardiac catheterization pressures, the regional myocardial contractility and stress distribution of a sheep with posterobasal infarction were investigated. Active material parameters in the noninfarcted border zone (BZ) myocardium adjacent to the infarct (Tmax_B), in the myocardium remote from the infarct (Tmax_R), and in the infarct (Tmax_I) were estimated by minimizing the errors between FE model-predicted and experimentally measured systolic strains and LV volumes using the previously developed optimization scheme. The optimized Tmax_B was found to be significantly depressed relative to Tmax_R, while Tmax_I was found to be zero. The myofiber stress in the BZ was found to be elevated, relative to the remote region. This could cause further damage to the contracting myocytes, leading to heart failure.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

3D cardiac strain analysis from in vivo tagged MRIs. Endocardial and epicardial contours as well as segmented tag lines were traced from (a) short-axis MRIs to create a 3D geometry. (b) Each short-axis slice was divided into 12 sectors, and a 4D B-spline-based motion tracking technique was applied to the tag-line (dotted lines) deformations in order to calculate the Lagrangian Green’s strains in cylindrical coordinates. For each sector of each short-axis slice, longitudinal, radial, (c) circumferential, and shear strains throughout systole were determined.

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Figure 4

Stress (kPa) in the myofiber direction at end-systole. The black lines represent the boundaries of the border zone. The stress is elevated in the border zone region, which is indicated by the red color contour.

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Figure 2

(a) Animal-specific finite element model used in the optimization method. The green elements represent the healthy remote region, the red elements are the border zone, and the blue elements are the infarcted region. (b) Cross-section view of the animal-specific finite element model near midventricle. It can be seen that the infarcted region is thinner than the surround myocardium. The red border zone is used to approximate the transition from healthy to diseased tissue.

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Figure 3

A comparison of the experimental and finite element (a) circumferential strain and (b) longitudinal strain in a slice near midventricle. On average, there is good agreement between the experimental and numerical strains in the remote, border zone, and infarct regions.

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