A group of 1939 NOMAS subjects underwent carotid ultrasonography within 1 year of enrollment. The mean age was 68.6±10.0 years with 41.0% male and 51.4% Hispanic. Carotid plaque was visualized in 1091 subjects (56.4%); 418 (21.6%) had one plaque, and 673 (34.7%) had more than one plaque. Median MCPT was 1.0 mm (75th percentile 1.8 mm). By plaque location, 1009 (52.0%) subjects had plaque in the internal carotid arteries or bifurcations only, whereas 82 (4.3%) had involvement of the common carotid segment; only 4 subjects had isolated common carotid artery plaque. Irregular plaque surface was recorded in 107 (5.5%) subjects, whereas 984 (51.8%) had regular plaques only. Of those with irregular surface, 36 (33.6%) were bilateral. Stenosis greater than 40% was present in only 68 subjects (3.6%). Other baseline demographic, vascular, and plaque characteristics of the cohort are presented in . During a mean follow-up time of 6.2 years, 89 subjects were diagnosed with strokes (4.6%), of which there were 69 ischemic strokes (3.6%), 102 myocardial infarctions (5.3%), 134 vascular deaths (6.9%), and 246 combined outcomes of IS, MI, or VD (12.7%).
Baseline Characteristics of the Cohort (n=1939)
shows the 5-year cumulative risks of IS, MI, VD, and combined outcomes stratified by plaque characteristic. The 5-year IS risk among those with irregular plaque surface was 8.5% versus 3.0% among those with regular surface (). Plaque surface irregularity (vs regular surface) was also associated with approximately 2 times greater 5-year cumulative risks of MI and VD, respectively. Subjects with carotid stenosis >60% had 13.4% 5-year risk of ischemic stroke, 23.6% for MI, and 17.8% for vascular death.
Unadjusted Cumulative 5-Year Risks of Vascular Events by Carotid Plaque Characteristic
Cumulative risk of ischemic stroke by plaque surface type. Log-rank test: P<0.01 for homogeneity across strata.
After adjusting for age, sex, race–ethnicity, level of education, current smoking, diabetes, hypertension, hypercholesterolemia, and cardiac disease, plaque surface irregularity (adjusted hazard ratio [HR], 4.0; 95% CI, 1.7 to 9.4) and carotid stenosis >60% (adjusted HR, 6.4; 95% CI, 2.2 to 18.7) significantly increased the risk for IS compared with no plaque (). Plaque number and location were not significantly predictive of ischemic stroke. However, carotid stenosis (40% to 60%: adjusted HR, 3.0; 95% CI, 1.2 to 7.4; >60%: adjusted HR, 5.0; 95% CI, 2.2 to 11.4), presence of >1 carotid plaque (adjusted HR, 1.7; 95% CI, 1.1 to 3.0), and common carotid artery plaque (adjusted HR, 2.6; 95% CI, 1.2 to 5.6) independently predicted MI. In addition, presence of common carotid artery plaque significantly elevated risk of VD (adjusted HR, 1.9; 95% CI, 1.0 to 3.6). Irregular plaque, stenosis of 40% to 60% and >60%, >1 plaque, and common carotid artery plaque were all predictive of the combined vascular outcome.
Adjusted HR (95% CI) for Vascular Outcomes Stratified by Carotid Plaque Characteristic (reference: no plaque)*
Compared with those with regular plaque surface, irregular plaque surface increased IS risk nearly 3-fold (adjusted HR, 2.7; 95% CI, 1.3 to 5.5). Having bilateral plaque surface irregularity (adjusted HR, 3.9; 95% CI, 1.4 to 11.0) increased the risk more than unilateral irregular surface with contralateral regular surface (adjusted HR, 2.6; 95% CI, 1.1 to 6.2). Of 10 IS among 107 subjects with irregular plaque surface, 7 were ipsilateral to the lesion.
We further adjusted for plaque thickness and degree of stenosis to remove their potential confounding effects on the relationship between plaque surface morphology and IS risk. In a final model adjusting for demographics, vascular risk factors, MCPT (< or ≥75th percentile), and categorical degree of stenosis (<40%, 40% to 60%, >60%), irregular plaque surface remained an independent predictor of IS risk (adjusted HR, 3.1; 95% CI, 1.1 to 8.8). Compared with regular plaque, the IS risk for irregular plaque surface was attenuated (adjusted HR, 2.3; 95% CI, 1.0 to 5.4).