Research Papers

A New Growth Model for Aortic Valve Calcification

[+] Author and Article Information
Rotem Halevi, Karin Lavon

School of Mechanical Engineering,
Tel-Aviv University,
Tel Aviv 69978, Israel

Ashraf Hamdan

Department of Cardiology,
Rabin Medical Center,
Petach Tikva 4941492, Israel

Gil Marom

School of Mechanical Engineering,
Tel-Aviv University,
Tel Aviv 69978, Israel;
Department of Biomedical Engineering,
Stony Brook University,
Stony Brook, NY 11794

Sagit Ben-Zekry

Echocardiography Laboratory,
Chaim Sheba Medical Center,
Tel Hashomer 52621, Israel

Ehud Raanani

Cardiothoracic Surgery Department,
Chaim Sheba Medical Center,
Tel Hashomer 52621, Israel

Rami Haj-Ali

School of Mechanical Engineering,
The Nathan Cummings Chair in Mechanics,
The Fleischman Faculty of Engineering,
Tel-Aviv University,
Tel Aviv 69978, Israel
e-mail: rami98@eng.tau.ac.il

1Corresponding author.

Manuscript received December 28, 2017; final manuscript received May 16, 2018; published online June 21, 2018. Assoc. Editor: Seungik Baek.

J Biomech Eng 140(10), 101008 (Jun 21, 2018) (8 pages) Paper No: BIO-17-1603; doi: 10.1115/1.4040338 History: Received December 28, 2017; Revised May 16, 2018

Calcific aortic valve disease (CAVD) is a progressive disease in which minerals accumulate in the tissue of the aortic valve cusps, stiffening them and preventing valve opening and closing. The process of valve calcification was found to be similar to that of bone formation including cell differentiation to osteoblast-like cells. Studies have shown the contribution of high strains to calcification initiation and growth process acceleration. In this paper, a new strain-based calcification growth model is proposed. The model aims to explain the unique shape of the calcification and other disease characteristics. The calcification process was divided into two stages: Calcification initiation and calcification growth. The initiation locations were based on previously published findings and a reverse calcification technique (RCT), which uses computed tomography (CT) scans of patients to reveal the calcification initiation point. The calcification growth process was simulated by a finite element model of one aortic valve cusp loaded with cyclic loading. Similar to Wolff's law, describing bone response to stress, our model uses strains to drive calcification formation. The simulation grows calcification from its initiation point to its full typical stenotic shape. Study results showed that the model was able to reproduce the typical calcification growth pattern and shape, suggesting that strain is the main driving force behind calcification progression. The simulation also sheds light on other disease characteristics, such as calcification growth acceleration as the disease progresses, as well as sensitivity to hypertension.

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Fig. 4

Reverse calcification technique representing calcification growth. Calcification of cusps number one and two initiates next to the arc bases. Calcification of cusp number three initiates at the top of the arc shape.

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Fig. 3

The model: (a) Stress–strain curves for the hyper-elastic materials in the root and for the collagen and elastin of the cusps, (b) a schematic description of the symmetric cusp with the location of the collagen fibers and (c) pin constrain (in the attachment line) and belly pressure. The coaptation region is the unloaded cusp area.

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Fig. 2

Tension plate model (a) principal strains. (b) Principal strains in the strain concentration area and at the remote field strain.

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Fig. 1

Typical calcification patterns with the number of cusps (n) and their percentage in the sample: (a) Typical initiation point, (b) arc shape calcification and second initiation point, and (c) partial arc shape. The light shade indicates later stage calcification.

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Fig. 5

Strain distribution comparison between full AV FSI with compliant model to the simplified model in use

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Fig. 6

Cusp belly max principal strains during calcification growth. The figures are presented without strain averaging, in order to better differentiate between calcification and the tissue.

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Fig. 7

Principal strain directions and magnitude: (a) Linear isotropic tissue material (no fibers), (b) analysis of the cusp without calcification, and (c) analysis of the cusp with partial arc calcification

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Fig. 8

Calcification growth results with triangular and quadrilateral elements, with initiation at the arc base and arc top

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Fig. 9

Comparison of algorithm result to CT scan of valve with arc and partial arc shape calcification



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