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Carotid-Wall Intima–Media Thickness and Cardiovascular Events
Study Questions:
What is the incremental prognostic value of intima–media thickness of the walls of the common carotid artery and internal carotid artery to the Framingham risk score for predicting cardiovascular events?
Methods:
The investigators measured the mean intima–media thickness of the common carotid artery and the maximum intima–media thickness of the internal carotid artery in 2,965 members of the Framingham Offspring Study cohort. Cardiovascular disease outcomes were evaluated for an average follow-up of 7.2 years. Multivariable Cox proportional hazards models were generated for intima–media thickness and risk factors. The authors evaluated the reclassification of cardiovascular disease on the basis of the 8-year Framingham risk score category (low, intermediate, or high) after adding intima–media thickness values.
Results:
A total of 296 participants had a cardiovascular event. The risk factors of the Framingham risk score predicted these events, with a c-statistic of 0.748 (95% confidence interval [CI], 0.719-0.776). The adjusted hazard ratio for cardiovascular disease with a 1-standard deviation increase in the mean intima–media thickness of the common carotid artery was 1.13 (95% CI, 1.02-1.24), with a nonsignificant change in the c-statistic of 0.003 (95% CI, 0.000-0.007); the corresponding hazard ratio for the maximum intima–media thickness of the internal carotid artery was 1.21 (95% CI, 1.13-1.29), with a modest increase in the c-statistic of 0.009 (95% CI, 0.003-0.016). The net reclassification index increased significantly after addition of intima–media thickness of the internal carotid artery (7.6%, p < 0.001), but not intima–media thickness of the common carotid artery (0.0%, p = 0.99). With the presence of plaque, defined as intima–media thickness of the internal carotid artery of more than 1.5 mm, the net reclassification index was 7.3% (p = 0.01), with an increase in the c-statistic of 0.014 (95% CI, 0.003-0.025).
Conclusions:
The authors concluded that the maximum intima–media thickness of (and presence of plaque in) the internal carotid artery significantly improves the classification of risk of cardiovascular disease in the Framingham Offspring Study cohort.
Perspective:
The study suggests that the intima–media thickness of the common carotid artery and the intima–media thickness of the internal carotid artery are independent predictors of cardiovascular events among participants in the Framingham Offspring Study. The maximum intima–media thickness of the internal carotid artery, as either a continuous measurement or a surrogate for the presence of plaque (above a threshold of 1.5 mm), contributed significantly but modestly to the predictive power of the risk factors used in calculating the Framingham risk score, and improved risk classification on the basis of the Framingham risk score. The results have the potential to influence future guidelines on how intima–media thickness is assessed for the primary prevention of cardiovascular disease.
Keywords: Follow-Up Studies, Plaque, Atherosclerotic, Carotid Intima-Media Thickness, Cardiovascular Diseases, Risk Factors, Carotid Artery, Internal, Primary Prevention
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