July 21st, 2011
Carotid IMT Provides Modest Improvement to Risk Prediction
Measurement of the maximum intima–media thickness (IMT) of the internal carotid artery (CA) can modestly improve cardiovascular risk prediction, according to a new study published in the New England Journal of Medicine. Joseph Polak and colleagues measured the mean IMT of the common CA and the maximum IMT of the internal CA of 2965 subjects taking part in the Framingham Offspring Study. The subjects were then followed for a mean of 7.2 years, and the value of adding IMT measurements to the Framingham Risk Score (FRS) was assessed.
Although adding the mean IMT of the common CA did not significantly improve risk prediction, the hazard ratio for a 1 standard-deviation increase in the maximum IMT of the internal CA was 1.21 (95% CI, 1.13-1.29), along with an increase in the C statistic that the authors called “modest” (0.009; 95% CI, 0.003-0.016). The use of maximum IMT of the internal CA also improved the assignment of the low-, intermediate-, or high-FRS categories, as measured by the net reclassification index. Finally, the presence of plaque greater than 1.5 mm in the IMT of the internal CA also improved the predictive power of the FRS.
In their discussion, the authors write that their results should have an impact on the current ACCF-AHA guidelines for primary prevention, as the current level IIa recommendation lacks a quantitative basis. They conclude that maximum IMT of the internal CA contributes “significantly but modestly to the predictive power of the risk factors used in calculating the Framingham risk score.”