Carotid Plaque Thickness Associated with Risk of Vascular Events in Hispanics

By Todd Neale
MIAMI, March 20 -- Hispanics with carotid plaque that is 1.9 millimeters thick or more have twice the risk of stroke, myocardial infarction, or other vascular events as people who are plaque-free, a cohort study revealed.
After adjustment for demographics and several cardiovascular risk factors, Hispanics had a hazard ratio of 2.22 (95% CI 1.30 to 3.78) for any vascular event, Tatjana Rundek, M.D., Ph.D., of the University of Miami, and colleagues, reported online in Neurology.
For the overall cohort (52% Caribbean Hispanic, 25% black, 15% white), the hazard ratio was 1.48 (95% CI 1.05 to 2.10), but the association was not significant among blacks or whites independently.
Dr. Rundek and colleagues showed in a previous study that Hispanics had a higher incidence of stroke compared with other ethnic groups.
"Taken together," they said, "these results may be of significant importance for the development of primary prevention programs for this vulnerable and the fastest growing minority population in the United States."
Although carotid atherosclerosis is a well-known risk factor for vascular disease, the risk associated with small, nonstenotic plaques is less clear, the researchers said.
High-resolution B-mode ultrasound may be an inexpensive, simple, and noninvasive means of measuring plaque thickness and identifying at-risk patients beyond conventional Framingham vascular risk factors, they said.
To examine the relationship between plaque thickness and risk of vascular events, Dr. Rundek and colleagues prospectively analyzed data from 2,189 participants (mean age 68 ± 10; 59.8% female) as part of the ongoing Northern Manhattan Study. All participants were stroke-free at enrollment and were followed up yearly by telephone.
The researchers used ultrasound to examine the carotid artery for plaque, which was defined as an area of thickening 50% greater than the thickness of the surrounding wall.
Plaque was present in 1,263 (58%) of participants and was more prevalent in those 65 and older, non-Hispanics, those with a history of hypertension, diabetes, or cardiac disease, current smokers, and those with an LDL cholesterol level of 130 or higher.
Mean maximum carotid plaque thickness was 1.1 ± 0.9 mm (range 0 to 8.0 mm).
Participants were divided into three categories, those with:
No plaque
Maximum carotid plaque thickness less than the 75th percentile of distribution within the cohort (<1.9 mm)
Maximum carotid plaque thickness of 1.9 mm or more
After a mean follow-up of 6.9 years, 121 participants had had an ischemic stroke, 118 had had an MI, and 166 had died from other vascular causes.
Overall, incidence rates for ischemic stroke, MI, or combined vascular events were highest for those participants with a maximum carotid plaque thickness of 1.9 mm or more (11.26, 13.42, and 34.59 per 1,000 person-years, in the three categories respectively).
The researchers noted that the incidence rate of ischemic stroke was noticeably higher than in previous studies. They suggested that the finding may be a consequence of a relatively higher age in their cohort.
When the participants were stratified by age, gender, and race/ethnicity, the association between a maximum carotid plaque thickness of 1.9 mm or more and an increased risk of any vascular event was significant only in Hispanics after adjusting for several factors. These included age, gender, race/ethnicity, education, hypertension, diabetes, LDL and HDL cholesterol levels, body mass index, smoking, alcohol consumption, and use of aspirin and lipid-lowering medication.
Presence of plaque may give physicians a better estimate of vascular risk than Framingham risk score alone, the researchers said.
"More than half of individuals in low and moderate [Framingham risk score] categories can be reclassified into the higher risk category if their information on presence of carotid plaque is available," they said.
Because their cohort consisted predominantly of Caribbean Hispanics, the results may not be generalizable to other Hispanic or racial/ethnic populations, the researchers noted.
They acknowledged other limitations, as well, including the lack of measurements on plaque area or volume, not evaluating the associations of maximum carotid plaque thickness with stroke subtype, and not accounting for the possibility that new vascular risk factors developed during follow-up.
"However," they said, "the prevalence of the risk factors such as hypertension and diabetes did not considerably change over time in our cohort."
The study was supported in part by the Gilbert Baum Memorial Grant and the Goddess Fund for Stroke Research in Women and by grants from the National Institute of Neurological Disorders and Stroke, the AHA, and the General Clinical Research Center.
The authors reported no conflicts of interest.
Primary source: NeurologySource reference:Rundek T, et al "Carotid plaque, a subclinical precursor of vascular events: The Northern Manhattan Study" Neurology 2008; DOI: 10.1212/01.wnl.0000303969.63165.34.