Effect of Detection of Subclinical Atherosclerosis on Carotid Ultrasound on Cardiovascular Events in a Primary Prevention Clinical Setting

BACKGROUND: The relative contribution of common carotid artery (CCA) intimal medial thickness (IMT), carotid bifurcation plaque presence, and its burden in predicting cardiovascular disease (CVD) events in a primary prevention clinical cohort remain unclear. AIMS: To assess the usefulness of distal far wall of right and left CCA IMT assessment (in the absence of carotid bifurcation plaque) and plaque presence and plaque number on incident CVD in a primary prevention clinical setting. METHODS: Observational study of consecutive 1,903 patients free of known CVD clinically referred for right and left carotid bifurcation two-dimensional ultrasound for subclinical atherosclerosis assessment between 2007 and 2014 at a single center. Incident composite CVD (cardiac death, myocardial infarction, unstable angina, and ischemic stroke) was compared between patients with and without plaque (defined as focal or diffuse medial-adventitial border to luminal border thickening of ≥1.5 mm), with increasing plaque number and with increasing CCA IMT percentiles (<25th, 25th-49th, 50th-74th, and >75th centiles) adjusted for atherosclerotic CVD scores using Pooled Cohort Equation and Framingham Risk Score in the absence of bifurcation plaque. RESULTS: The final study cohort contained 1,569 patients (mean age, 55.1 ± 8.6 years; female, 36%) after study exclusions with a mean follow-up of 9.8 ± 5.5 years. Eight hundred fifty-nine (54.7%) had carotid plaque, and 710 (45.3%) had no plaque. Incident composite CVD occurred in 90 (5.7%) patients, with no difference in patients with and without plaque (hazard ratio [HR] = 1.19; 95% CI, 0.78-1.82; P = .425) or with ≥75th versus <75th IMT percentile in the absence of plaque (HR = 1.35; 95% CI, 0.64-2.85; P = .431). Increased incident CVD events occurred in patients with 3 or more plaques versus no plaque (HR = 2.9; 95% CI, 1.48-5.65; P = .002), which remained significant after adjusting for the Pooled Cohort Equation (HR = 2.45; 95% CI, 1.13-5.3; P = .023) and Framingham Risk Score. Patients with IMT centile ≥75% and presence of carotid plaque received increasing new statin prescriptions after carotid ultrasound result. Significant low-density lipoprotein cholesterol reduction (19.3 ± 25.7 mg/dL; P < .001) on follow-up occurred only in patients in whom plaque was identified. CONCLUSIONS: The number of carotid bifurcation plaques on carotid ultrasound is associated with incident CVD in a primary prevention cohort. Given the referral nature of the study cohort, evaluation of only carotid vascular bed, and increased statin prescriptions after carotid ultrasound result, our findings regarding the lack of prognostic value of CCA IMT or of any plaque should be interpreted with caution. Presence of plaque on carotid ultrasound led to increased statin prescriptions and greater low-density lipoprotein cholesterol reduction on follow-up. This clinically useful and simple method can be adopted in clinical practice for CVD risk stratification.