Carotid Bifurcation Geometry Is an Independent Predictor of Early Wall Thickening at the Carotid Bulb

Abstract

Background and Purpose Lumen geometry has long been suspected as a risk factor for atherosclerosis by virtue of its influence on blood flow disturbances. Confirmation of this geometric risk hypothesis has, however, proved challenging owing to possible effects of wall thickening on geometry, and unproven links between candidate geometric variables and disturbed flow. The purpose of this study was to overcome these challenges. Methods The study relied on imaging and risk factor data from progressively refined subsets of the Atherosclerosis Risk in Communities (ARIC) Carotid MRI study. Group 1 (N=467) included only non-stenotic cases having sufficient-quality angiography for 3D analysis. Group 2 (N=346) excluded cases from Group 1 having common and internal carotid artery (ICA) wall thickness above previously-identified thresholds for inward remodeling. Group 3 (N=294) excluded cases from Group 2 having lumen irregularities, and thus was least likely to include lumen geometries influenced by wall thickening. Results Multiple linear regressions showed that for Group 3 bifurcation flare and proximal curvature were independent predictors of ICA wall thickness, consistent with their previously-demonstrated roles in predicting disturbed flow. For the broadest Group 1, flare was an independent predictor of ICA wall thickness, but with a sign change in regression coefficient reflecting effects of wall thickening on lumen geometry. Conclusion Carotid bifurcation geometry is an independent, albeit weak, predictor of its early wall thickening, but only when assumptions about geometric factors, and the influence of disease on them, are confronted. This highlights pitfalls of previous attempts to confirm geometric risk of atherosclerosis.

Morphometric and hemodynamic analysis of atherosclerotic progression in human carotid artery bifurcations

“…28 Ϯ 11°, P ϭ 0.52) and 4 (46 Ϯ 17°vs. 51 Ϯ 16°, P ϭ 0.14), which was consistent with the results of Bijari et al (3). In contrast, Phan et al (23) found a significant increase of the ICA angle in adults with mild and severe stenoses.…”

“…Although a complete comparison showed significant difference of carotid artery bifurcations between control subjects and patients with carotid artery disease, the sample size (30 control subjects and 30 patients with carotid artery disease) in the retrospective study was relatively small compared with previous studies (3,23). This requires further analysis with larger sample size in a prospective study.…”

“…The ECA diameter in patients with carotid artery disease was significantly reduced (P Ͻ 0.05), while the CCA diameter was not statistically different from the control (P ϭ 0.18). Moreover, Patients [25][26][27][28][29][30] in Table 4, who were the youngest (ages 40 Ϯ 6 yr) and had extension of stenosis to the entire cervical ICA, showed smaller diameters of CCA and ECA than Patients [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] (ages 54 Ϯ 12 yr) with no stenoses in the distal regions of ICA. Patients 19 -24 in Table 4, who were the oldest (ages 71 Ϯ 7 yr) and had extension of stenosis to the middle of cervical ICA, showed larger angle 2 than Patients 1-18 and Patients [25][26][27][28][29][30] despite the lack of significant difference of angle 1.…”

“…3, A-C, show the variation of D fit along normalized ICA center lines with the stenosis near bifurcation (Patients [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] ) and in the middle of the vessel (Patients 19 -24 ) and with extension to the entire vessel (Patients [25][26][27][28][29][30] ), respectively. The black line, "control," represents the mean value of D fit (averaged over all controls) and error bars refer to SD.…”

“…Atherosclerotic plaques usually reside in artery bifurcations with complex flow patterns (6,7,10,13,15,17). Because of its clinical relevance to stroke (9), the morphometry of human carotid artery bifurcation [comprised of the left and right common (CCA), internal (ICA), and external (ECA) carotid arteries] (16) has received intensive investigation (3,23,24,27). Researchers have proposed various geometric risk factors for the incidence of atherosclerotic plaques, e.g., increased bifurcation angle and enhanced differences in area ratios including the flare, proximal curvature, and tortuosity of ICA.…”