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Technical Briefs

A Novel Method for Quantifying In-Vivo Regional Left Ventricular Myocardial Contractility in the Border Zone of a Myocardial Infarction

[+] Author and Article Information
Lik Chuan Lee1

Departments of Surgery and Bioengineering,  University of California, San Francisco, CA 94143; Department of Veterans Affairs Medical Center, San Francisco, CA 94121likchuan@berkeley.edu

Jonathan F. Wenk, Doron Klepach, Liang Ge, Mark B. Ratcliffe, Julius M. Guccione

Departments of Surgery and Bioengineering,  University of California, San Francisco, CA 94143; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

Zhihong Zhang

Department of Surgery,  University of California, San Francisco, CA 94143; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

David Saloner

Department of Radiology,  University of California, San Francisco, CA 94143; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

Arthur W. Wallace

Department of Anesthesia,  University of California, San Francisco, CA 94143; Department of Veterans Affairs Medical Center, San Francisco, CA 94121

1

Corresponding author. Present address: Division of Surgical Services (112D), Department of Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA, 94121.

J Biomech Eng 133(9), 094506 (Oct 11, 2011) (5 pages) doi:10.1115/1.4004995 History: Received July 10, 2011; Accepted August 24, 2011; Published October 11, 2011; Online October 11, 2011

Homogeneous contractility is usually assigned to the remote region, border zone (BZ), and the infarct in existing infarcted left ventricle (LV) mathematical models. Within the LV, the contractile function is therefore discontinuous. Here, we hypothesize that the BZ may in fact define a smooth linear transition in contractility between the remote region and the infarct. To test this hypothesis, we developed a mathematical model of a sheep LV having an anteroapical infarct with linearly–varying BZ contractility. Using an existing optimization method (Sun , 2009, “A Computationally Efficient Formal Optimization of Regional Myocardial Contractility in a Sheep With Left Ventricular Aneurysm,” J. Biomech. Eng., 131 (11), pp. 111001), we use that model to extract active material parameter Tmax and BZ width dn that “best” predict in–vivo systolic strain fields measured from tagged magnetic resonance images (MRI). We confirm our hypothesis by showing that our model, compared to one that has homogeneous contractility assigned in each region, reduces the mean square errors between the predicted and the measured strain fields. Because the peak fiber stress differs significantly (∼15%) between these two models, our result suggests that future mathematical LV models, particularly those used to analyze myocardial infarction treatment, should account for a smooth linear transition in contractility within the BZ.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 2

Optimization results: (a) convergence with BZ width dn as a parameter and (b) converged value of OBJ versus dn

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Figure 3

Contractility in the border zone. dn  = 3 cm. Tmax-R  = 186.3kPa

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Figure 4

Comparison of stress in myofiber direction at ES. (a) Linearly–varying Tmax-BZ with dn  = 3cm and Tmax-R  = 186.3 kPa. (b) Homogeneous Tmax-BZ with Tmax-R  = 190.1kPa and Tmax-BZ  = 60.3kPa. Unit of fringe levels in kPa.

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Figure 1

Sheep LV with anteroapical aneurysm. (a) Finite element mesh and (b) contractility Tmax in BZ. Dotted line: homogeneous Tmax in BZ. Solid line: linearly–varying Tmax with distance d in BZ.

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