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Shear stress metrics associated with pro-atherogenic high-risk anatomical features in a carotid artery bifurcation
Nora C Zalud1, Kartik V Bulusu1, Michael W Plesniak2
1Department of Mechanical and Aerospace Engineering, The George Washington University, 800 22nd Street NW, Science & Engineering Hall, Suite 3000, Washington, DC 20052, United States.
Insights
Carotid artery geometry significantly impacts atherosclerosis risk. High-risk anatomy promotes plaque formation through altered blood flow and shear stress patterns, identified by the oscillatory shear index.
Area of Science:
- Biomedical Engineering
- Fluid Dynamics
- Cardiovascular Research
Background:
- Atherosclerotic plaques in the carotid artery are a leading cause of mortality in the US.
- Blood flow shear stress is a known trigger for plaque formation.
- The internal carotid artery sinus is susceptible to atherosclerosis, but predisposition factors remain unclear.
Purpose of the Study:
- To computationally investigate how carotid artery geometry influences wall shear stress distribution.
- To compare flow dynamics and shear stress metrics between low-risk and high-risk carotid artery anatomies.
- To identify geometric features contributing to atherosclerosis risk.
Main Methods:
- Computational fluid dynamics modeling of carotid artery bifurcations.
- Comparison of flow fields and wall shear stress (WSS) metrics between low-risk and high-risk geometries.
- Utilized patient-averaged anatomical data and physiological inflow waveforms.
Main Results:
- The high-risk geometry exhibited increased flow separation and a more equal flow split at the bifurcation.
- Reduced internal carotid artery flow rate and increased low-velocity areas were observed in the high-risk model.
- The high-risk geometry showed significantly higher oscillatory shear index (OSI) values, particularly on the sinus wall and distal outer walls.
Conclusions:
- The oscillatory shear index (OSI) effectively identifies pro-atherogenic geometric features, augmenting traditional time-averaged wall shear stress (TAWSS) analysis.
- Flow split at the carotid bifurcation is a potential clinical indicator for atherosclerosis risk, accessible via imaging.
Background:
Diseases associated with atherosclerotic plaques in the carotid artery are a major cause of deaths in the United States. Blood-flow-induced shear-stresses are known to trigger plaque formation. Prior literature suggests that the internal carotid artery sinus is prone to atherosclerosis, but there is limited understanding of why only certain patients are predisposed towards plaque formation.
Methods:
We computationally investigate the effect of vessel geometry on wall-shear-stress distribution by comparing flowfields and wall-shear-stress-metrics between a low-risk and a novel predisposed high-risk carotid artery bifurcation anatomy. Both models were developed based on clinical risk estimations and patient-averaged anatomical features. The high-risk geometry has a larger internal carotid artery branching angle and a lower internal-to-carotid-artery-diameter-ratio. A patient-averaged physiological carotid artery inflow waveform is used.
Findings:
The high-risk geometry experiences stronger flow separation in the sinus. Furthermore, it experiences a more equal flow split at the bifurcation, thereby reducing internal carotid artery flowrate and increasing atherosclerosis-prone low-velocity areas. Lowest time-averaged-wall-shear-stresses are present at the sinus outer wall, where plaques are often found, for both geometries. The high-risk geometry has significantly high, unfavorable oscillatory-shear-index values not found in the low-risk geometry. High oscillatory-shear-index areas are located at the vessels outside walls distal to the bifurcation and on the sinus wall.
Interpretation:
These results highlight the effectiveness of oscillatory-shear-index, to augment classical time-averaged-wall-shear-stress, in evaluating pro-atherogenic geometry features. Furthermore, the flow split at the bifurcation is a promising clinical indicator for atherosclerosis risk as it can be directly accessed using clinical imaging, whereas shear-stress-metrics cannot.
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