Abstract P368: Carotid Intima-Medial Thickness is Associated with Silent Brain Infarctions: The Atherosclerosis Risk in Communities Study

Abstract

Background: Carotid intima-medial thickness (IMT) is an indicator of subclinical atherosclerosis and medial hypertrophy, and is easily quantified by ultrasonography. Although carotid IMT has been associated with systemic cardiovascular disease, its relation to silent brain infarctions (SBI) is not well established. The etiology of SBI is multifactorial; likely causes include atherosclerotic and thrombotic obstructions, microthrombi, and lipohyalinosis. Because arterial IMT reflects both atherogenesis and hypertensive remodeling, we hypothesized that elevated carotid IMT would be associated with SBI. Methods: The Atherosclerosis Risk in Communities (ARIC) study is an observational cohort of 15,792 black and white participants from 4 US communities. At visit 3 (1993-1995) a subset of stroke-free study participants (N=1,346) was screened by brain MRI and carotid ultrasound. IMT was averaged bilaterally, from 12 posterior wall measurements along a 1 cm segment of the distal common carotid artery up to the bifurcation. Consistent with European Society of Cardiology recommendations, IMT > 0.9 mm was considered elevated. Asymptomatic brain lesions ≥3 mm in diameter were considered SBI. Prevalence ratios (PRs) for number of SBI lesions associated with elevated IMT were analyzed using Poisson regression, adjusted for age, race-center, sex, current smoking, hypertension, diabetes, and hyperlipidemia. Model fit was ascertained by the deviance to degree of freedom ratio. Results: Of 1,346 individuals, 170 (13%) were classified with elevated IMT. Mean IMT was 1.0 ± 0.2 mm vs. 0.7 ± 0.1 mm for those with and without elevated IMT. Study participants with elevated IMT were more often male (49% vs. 38%; p=0.006), black (60% vs. 46%; p=0.0007), and older (64 vs. 62 years; p=0.0001); with a greater prevalence of both hypertension (65% vs. 42%; p<0.0001) and diabetes (27% vs. 13%; p<0.0001). SBI were detected in 157 individuals with a collective total of 247 lesions. A total of 30 (18%) participants with elevated IMT had at least one SBI lesion, compared to 127 (11%) with normal IMT (p=0.009). Elevated IMT was associated with 70% greater number of SBI lesions (PR=1.7; 95% CI: 1.3 - 2.3; p=0.0008). After adjustment for cardiovascular risk factors, elevated IMT remained associated with a 40% greater SBI count (PR= 1.4; 95% CI: 1.0 - 1.9; p=0.05). Conclusions: Although elevated IMT is often classified by a conservative 0.9 mm cut-point, it is a continuum, with advanced wall thickening (>1.5 mm) recognized as plaque. In this analysis from the ARIC Study, asymptomatic individuals classified with elevated IMT had mild wall thickening (mean IMT = 1.0 mm), which nonetheless was associated with greater number of SBI lesions. This association remains robust after adjustment for cardiovascular risk factors.