Varying Definitions of Carotid Intima-Media Thickness and Future Cardiovascular Disease: A Systematic Review and Meta-Analysis

BACKGROUND: Carotid intima-media thickness (cIMT) has been widely used as a predictor of future cardiovascular disease (CVD); however, various definitions of cIMT exist. This study provides a systematic review and meta-analysis of the associations between different cIMT definitions and CVD. METHODS AND RESULTS: A systematic review of the different cIMT definitions used in prospective cohort studies was performed. The relationships between cIMT of different definitions (common carotid artery IMT [CCA-IMT], internal carotid artery IMT [ICA-IMT], combined segments [combined-IMT], mean CCA-IMT, and maximum CCA-IMT) with future stroke, myocardial infarction (MI), and CVD events were analyzed using random effects models. Among 2287 articles, 18 articles (14 studies) with >10 different cIMT definitions were identified and included in our meta-analysis. After adjusting for age and sex, a 1-SD increase in CCA-IMT was associated with future stroke (hazard ratio [HR], 1.32 [95% CI, 1.27-1.38]), MI (HR, 1.27 [95% CI, 1.22-1.33]), and CVD events (HR, 1.28 [95% CI, 1.19-1.37]). A 1-SD increase in ICA-IMT was related to future stroke (HR, 1.25 [95% CI, 1.11-1.42]) and CVD events (HR, 1.25 [95% CI, 1.04-1.50]) but not MI (HR, 1.26 [95% CI, 0.98-1.61]). A 1-SD increase in combined-IMT was associated with future stroke (HR, 1.30 [95% CI, 1.08-1.57]) and CVD events (HR, 1.36 [95% CI, 1.23-1.49]). Maximum CCA-IMT was more strongly related than mean CCA-IMT with risk of MI, and both measures were similarly associated with stroke and CVD events. CONCLUSIONS: Combined-IMT is more strongly associated with CVD events compared with single-segment cIMT definitions. Maximum CCA-IMT shows a stronger association with MI than mean CCA-IMT. Further research is warranted to validate our findings and to standardize the cIMT measurement protocol, as well as to explore underlying mechanisms.