Prediction of cardiovascular events with carotid IMT: a meta-analysis

Intima media thickness (IMT) of the carotid system is increasingly used as a surrogate marker for atherosclerosis. Its use relies on its ability to predict future clinical cardiovascular endpoints. In the present study, we performed a systematic review and meta-analysis of data examining this association.

Using a pre-specified MedLine search strategy, we identified eight relevant studies which were published until January 2006. We compared study design, measurement protocols and reported data and identified sources of heterogeneity between studies. To obtain a pooled estimate of the relative risk per IMT difference, we performed a meta-analysis based on random effects models. The age- and sex-adjusted overall estimate of the relative risk of myocardial infarction was 1.26 (95% CI: [1.21–1.30]) per one standard deviation (SD) common carotid artery (CCA) IMT difference and 1.15 [1.12–1.17] per 0.10mm CCA-IMT difference (n=30162 subjects). The age- and sex-adjusted relative risk of stroke was 1.32 [1.27–1.38] per one SD CCA-IMT difference and 1.18 [1.16–1.21] per 0.10mm CCA-IMT difference (n=34335 subjects). Major sources of heterogeneity were age distribution, carotid segment definition, and IMT measurement protocol. The relationship between IMT and risk was non-linear, but the linear models fitted relatively well for moderate to high IMT values.

Carotid IMT is a strong and reliable predictor of future vascular events. The relative risk per IMT difference is slightly higher for the endpoint stroke, compared to myocardial infarction. In future IMT studies, ultrasound protocols should be aligned with published studies. Data for younger individuals are limited and more studies are required.