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Effects of intima stiffness and plaque morphology on peak cap stress.

Akyildiz AC, Speelman L, van Brummelen H, Gutiérrez MA, Virmani R, van der Lugt A, van der Steen AF, Wentzel JJ, Gijsen FJ - Biomed Eng Online (2011)

Bottom Line: The peak cap stress increased three-fold when the cap thickness was reduced from 0.25 mm to 0.05 mm for both stiff and intermediate intima models.Two-fold increase in the intima thickness behind the necrotic core reduced the peak cap stress by approximately 25% for both intima models.Adventitia thickness and local media regression had limited effects for all three intima models.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Engineering, Thoraxcenter, Erasmus Medical Center, Rotterdam, the Netherlands. a.akyildiz@erasmusmc.nl

ABSTRACT

Background: Rupture of the cap of a vulnerable plaque present in a coronary vessel may cause myocardial infarction and death. Cap rupture occurs when the peak cap stress exceeds the cap strength. The mechanical stress within a cap depends on the plaque morphology and the material characteristics of the plaque components. A parametric study was conducted to assess the effect of intima stiffness and plaque morphology on peak cap stress.

Methods: Models with idealized geometries based on histology images of human coronary arteries were generated by varying geometric plaque features. The constructed multi-layer models contained adventitia, media, intima, and necrotic core sections. For adventitia and media layers, anisotropic hyperelastic material models were used. For necrotic core and intima sections, isotropic hyperelastic material models were employed. Three different intima stiffness values were used to cover the wide range reported in literature. According to the intima stiffness, the models were classified as stiff, intermediate and soft intima models. Finite element method was used to compute peak cap stress.

Results: The intima stiffness was an essential determinant of cap stresses. The computed peak cap stresses for the soft intima models were much lower than for stiff and intermediate intima models. Intima stiffness also affected the influence of morphological parameters on cap stresses. For the stiff and intermediate intima models, the cap thickness and necrotic core thickness were the most important determinants of cap stresses. The peak cap stress increased three-fold when the cap thickness was reduced from 0.25 mm to 0.05 mm for both stiff and intermediate intima models. Doubling the thickness of the necrotic core elevated the peak cap stress by 60% for the stiff intima models and by 90% for the intermediate intima models. Two-fold increase in the intima thickness behind the necrotic core reduced the peak cap stress by approximately 25% for both intima models. For the soft intima models, cap thickness was less critical and changed the peak cap stress by 55%. However, the necrotic core thickness was more influential and changed the peak cap stress by 100%. The necrotic core angle emerged as a critical determinant of cap stresses where a larger angle lowered the cap stresses. Contrary to the stiff and intermediate intima models, a thicker intima behind the necrotic core increased the peak cap stress by approximately 25% for the soft intima models. Adventitia thickness and local media regression had limited effects for all three intima models.

Conclusions: For the stiff and intermediate intima models, the cap thickness was the most important morphological risk factor. However for soft intima models, the necrotic core thickness and necrotic core angle had a bigger impact on the peak cap stress. We therefore need to enhance our knowledge of intima material properties if we want to derive critical morphological plaque features for risk evaluation.

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Influence of the necrotic core thickness and intima stiffness on the peak cap stress for the baseline geometry. Constant parameter values for the models: cap thickness = 0.05 mm, intima thickness behind the necrotic core = 0.5 mm, adventitia thickness = 0.15 mm, media thickness = 0.25 mm, necrotic core angle = 30°. Peak cap stress values and the undeformed geometries of some models are attached to the associated columns. The Young's modulus (E) values for the intima: 33 kPa for soft, 500 kPa for intermediate and 1000 kPa for stiff.
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Figure 5: Influence of the necrotic core thickness and intima stiffness on the peak cap stress for the baseline geometry. Constant parameter values for the models: cap thickness = 0.05 mm, intima thickness behind the necrotic core = 0.5 mm, adventitia thickness = 0.15 mm, media thickness = 0.25 mm, necrotic core angle = 30°. Peak cap stress values and the undeformed geometries of some models are attached to the associated columns. The Young's modulus (E) values for the intima: 33 kPa for soft, 500 kPa for intermediate and 1000 kPa for stiff.

Mentions: An example of the numerical results is shown in figure 3 where the computed stress map of a plaque half cross-section is presented. The peak cap stresses in the models mainly occurred in the midcap region. However, the difference between the peak cap stresses in the shoulder region and the midcap was small and never exceeded 5%. Generally, the results for all simulations were identical when using maximum principal stresses instead of von Mises stresses. In the remaining part of the paper, only the peak stresses in the midcaps are presented. Overall, more than 1000 simulations were performed to evaluate single and combined effects of geometric plaque parameter variations for the three intima models. The geometric variation we investigated will be illustrated by discussing two relevant examples in detail (figure 4 and 5). The main findings are presented in Table 3 and will be summarized at the end of the section.


Effects of intima stiffness and plaque morphology on peak cap stress.

Akyildiz AC, Speelman L, van Brummelen H, Gutiérrez MA, Virmani R, van der Lugt A, van der Steen AF, Wentzel JJ, Gijsen FJ - Biomed Eng Online (2011)

Influence of the necrotic core thickness and intima stiffness on the peak cap stress for the baseline geometry. Constant parameter values for the models: cap thickness = 0.05 mm, intima thickness behind the necrotic core = 0.5 mm, adventitia thickness = 0.15 mm, media thickness = 0.25 mm, necrotic core angle = 30°. Peak cap stress values and the undeformed geometries of some models are attached to the associated columns. The Young's modulus (E) values for the intima: 33 kPa for soft, 500 kPa for intermediate and 1000 kPa for stiff.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3090737&req=5

Figure 5: Influence of the necrotic core thickness and intima stiffness on the peak cap stress for the baseline geometry. Constant parameter values for the models: cap thickness = 0.05 mm, intima thickness behind the necrotic core = 0.5 mm, adventitia thickness = 0.15 mm, media thickness = 0.25 mm, necrotic core angle = 30°. Peak cap stress values and the undeformed geometries of some models are attached to the associated columns. The Young's modulus (E) values for the intima: 33 kPa for soft, 500 kPa for intermediate and 1000 kPa for stiff.
Mentions: An example of the numerical results is shown in figure 3 where the computed stress map of a plaque half cross-section is presented. The peak cap stresses in the models mainly occurred in the midcap region. However, the difference between the peak cap stresses in the shoulder region and the midcap was small and never exceeded 5%. Generally, the results for all simulations were identical when using maximum principal stresses instead of von Mises stresses. In the remaining part of the paper, only the peak stresses in the midcaps are presented. Overall, more than 1000 simulations were performed to evaluate single and combined effects of geometric plaque parameter variations for the three intima models. The geometric variation we investigated will be illustrated by discussing two relevant examples in detail (figure 4 and 5). The main findings are presented in Table 3 and will be summarized at the end of the section.

Bottom Line: The peak cap stress increased three-fold when the cap thickness was reduced from 0.25 mm to 0.05 mm for both stiff and intermediate intima models.Two-fold increase in the intima thickness behind the necrotic core reduced the peak cap stress by approximately 25% for both intima models.Adventitia thickness and local media regression had limited effects for all three intima models.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biomedical Engineering, Thoraxcenter, Erasmus Medical Center, Rotterdam, the Netherlands. a.akyildiz@erasmusmc.nl

ABSTRACT

Background: Rupture of the cap of a vulnerable plaque present in a coronary vessel may cause myocardial infarction and death. Cap rupture occurs when the peak cap stress exceeds the cap strength. The mechanical stress within a cap depends on the plaque morphology and the material characteristics of the plaque components. A parametric study was conducted to assess the effect of intima stiffness and plaque morphology on peak cap stress.

Methods: Models with idealized geometries based on histology images of human coronary arteries were generated by varying geometric plaque features. The constructed multi-layer models contained adventitia, media, intima, and necrotic core sections. For adventitia and media layers, anisotropic hyperelastic material models were used. For necrotic core and intima sections, isotropic hyperelastic material models were employed. Three different intima stiffness values were used to cover the wide range reported in literature. According to the intima stiffness, the models were classified as stiff, intermediate and soft intima models. Finite element method was used to compute peak cap stress.

Results: The intima stiffness was an essential determinant of cap stresses. The computed peak cap stresses for the soft intima models were much lower than for stiff and intermediate intima models. Intima stiffness also affected the influence of morphological parameters on cap stresses. For the stiff and intermediate intima models, the cap thickness and necrotic core thickness were the most important determinants of cap stresses. The peak cap stress increased three-fold when the cap thickness was reduced from 0.25 mm to 0.05 mm for both stiff and intermediate intima models. Doubling the thickness of the necrotic core elevated the peak cap stress by 60% for the stiff intima models and by 90% for the intermediate intima models. Two-fold increase in the intima thickness behind the necrotic core reduced the peak cap stress by approximately 25% for both intima models. For the soft intima models, cap thickness was less critical and changed the peak cap stress by 55%. However, the necrotic core thickness was more influential and changed the peak cap stress by 100%. The necrotic core angle emerged as a critical determinant of cap stresses where a larger angle lowered the cap stresses. Contrary to the stiff and intermediate intima models, a thicker intima behind the necrotic core increased the peak cap stress by approximately 25% for the soft intima models. Adventitia thickness and local media regression had limited effects for all three intima models.

Conclusions: For the stiff and intermediate intima models, the cap thickness was the most important morphological risk factor. However for soft intima models, the necrotic core thickness and necrotic core angle had a bigger impact on the peak cap stress. We therefore need to enhance our knowledge of intima material properties if we want to derive critical morphological plaque features for risk evaluation.

Show MeSH
Related in: MedlinePlus