Research Papers

Impact of Calcium Quantifications on Stent Expansions

[+] Author and Article Information
Pengfei Dong

Department of Mechanical and
Materials Engineering,
University of Nebraska-Lincoln,
Lincoln, NE 68588-0656

Hiram G. Bezerra

Vascular Institute,
University Hospitals Case Medical Center,
Cleveland, OH 44106

David L. Wilson

Department of Biomedical
Engineering and Radiology,
Case Western Reserve University,
Cleveland, OH 44106-7207

Linxia Gu

Department of Mechanical and
Materials Engineering,
University of Nebraska-Lincoln,
Lincoln, NE 68588-0656
e-mail: lgu2@unl.edu

1Corresponding author.

Manuscript received March 2, 2018; final manuscript received November 1, 2018; published online December 12, 2018. Assoc. Editor: Raffaella De Vita.

J Biomech Eng 141(2), 021010 (Dec 12, 2018) (8 pages) Paper No: BIO-18-1114; doi: 10.1115/1.4042013 History: Received March 02, 2018; Revised November 01, 2018

Severely calcified plaque is of great concern when planning and implementing a stenting intervention. In this work, computational models were developed to investigate the influence of calcium characteristics on stenting outcomes. The commonly used clinical measurements of calcium (i.e., the arc angle, maximum thickness, length, and volume) were varied to estimate stenting outcomes in terms of lumen gain, stent underexpansion, strut malapposition, and stress or strain distributions of the stenotic lesion. Results have shown that stenting outcomes were most sensitive to the arc angle of the calcium. A thick calcium with a large arc angle resulted in poor stenting outcomes, such as severe stent underexpansion, D-shaped lumen, increased strut malapposition, and large stresses or strains in the plaque. This was attributed to the circumferential stretch of the tissue. Specifically, the noncalcium component was stretched significantly more than the calcium. The circumferential stretch ratios of calcium and noncalcium component were approximately 1.44 and 2.35, respectively, regardless of calcium characteristics. In addition, the peak stress or strain within the artery and noncalcium component of the plaque occurred at the area adjacent to calcium edges (i.e., the interface between the calcium and the noncalcium component) coincident with the location of peak malapposition. It is worth noting that calcium played a protective role for the artery underneath, which was at the expense of the overstretch and stress concentrations in the other portion of the artery. These detailed mechanistic quantifications could be used to provide a fundamental understanding of the impact of calcium quantifications on stent expansions, as well as to exploit their potential for a better preclinical strategy.

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Grahic Jump Location
Fig. 1

Representative model of the stent-plaque-artery interaction (top), where the calcium has the length (L) of 5 mm, the arc angle (θ) of 270 deg, and maximum thickness (δ) of 0.06 mm (bottom)

Grahic Jump Location
Fig. 2

Minimal lumen area in relation to the combination of arc angle and volume of the calcium. The MLA had no correlation with the volume, but it was reduced with a large calcium angle.

Grahic Jump Location
Fig. 3

Stent induced stretch ratio (a) minimal lumen area of Ca 270-0.6-13 before (left) and after (right) stenting. (b) Five models with the same calcium length of 13 mm. Minimal alternations in the stretch ratio of each plaque components were observed regardless of the calcium angle and thickness (CaθδNLN: θ represented the degree of calcium angle, δN represented the maximum thickness in mm, and LN represented the longitudinal length in mm).

Grahic Jump Location
Fig. 4

Transvers plane cut of the stented artery for five models with a calcium length of 13 mm. A thicker calcium with a large angle resulted in a D-shaped lumen and more malapposition areas (CaθδNLN: θ represented the degree of calcium angle, δN represented the maximum thickness in mm, and LN represented the longitudinal length in mm).

Grahic Jump Location
Fig. 5

Malapposition of the stent struts (longitudinal plane cut) for models with different length Ca 270-0.6-13 (top) and Ca 270-0.6-5 (bottom) (CaθδNLN: θ represented the degree of calcium angle, δN represented the maximum thickness in mm, and LN represented the longitudinal length in mm)

Grahic Jump Location
Fig. 6

Stress distribution in the artery at fully expansion of the stent (left) and after recoil (right). During stent expansion, the percentage of high stresses increased with a large calcium angle or a large thickness, while it exhibited an opposite trend after the recoil (CaθδNLN: θ represented the degree of calcium angle, δN represented the maximum thickness in mm, and LN represented the longitudinal length in mm).

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Fig. 7

Strain histogram in the calcium at fully expansion (top) and after recoil (bottom). The peak MPS as well as the volume of higher strain in the calcium increased with a larger calcium angle and a thinner calcium (CaθδNLN: θ represented the degree of calcium angle, δN represented the maximum thickness in mm, and LN represented the longitudinal length in mm).

Grahic Jump Location
Fig. 8

Strain distribution in the noncalcium component of the plaque, with the peak value at the interface between calcium and the noncalcium components (CaθδNLN: θ represented the degree of calcium angle, δN represented the maximum thickness in mm, and LN represented the longitudinal length in mm)



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