Carotid intima-media thickness measurements: What defines an abnormality? A systematic review

Objective: In light of tremendous interest in and speculation about the implications of carotid artery intima-media thickness (IMT) measurements in clinical decision-making, the authors reviewed currently available information on IMT measurements in normal subjects and created a framework that can be used to define an abnormal result. Data sources: A search of MEDLINE and Current Contents, complemented by detailed analysis of references in the papers identified. Study selection: Population studies pertaining to IMT measurements in normal subjects were selected. Data extraction: Methods of measurement of carotid artery IMT, mean IMT by age and sex, IMT progression rates, and relation of IMT to risk of coronary and cerebrovascular events. Data synthesis: Although reports were from different populations and used differing techniques and equipment, the reported IMT measurements showed a consistent progression with age and greater values among men. Studies comparing the IMT between abnormal and normal groups show that most of the abnormal IMT measurements are above the 75th percentile of the mean common carotid artery IMT in normal subjects. Studies relating IMT measurements to the risk of coronary and cerebrovascular events show that the risk of first myocardial infarction increases with an IMT of 0.822 mm or more and the risk of stroke with an IMT of 0.75 mm or more. A progression rate of the far-wall common carotid artery IMT of 0.034 mm per year or greater increases the risk of future events significantly. Conclusions: An aggregated framework based on studies in differing age groups may be useful for assessing carotid vascular abnormalities as an aid to defining abnormalities and predicting risk in individual patients.