Carotid Intima‐Media Thickness and Prediction of Cardiovascular Disease

C arotid intima-media thickness (IMT) may be measured by ultrasound, where the distance between a double-line reflex pattern representing the luminal-intimal and the medialadventitial interfaces corresponds well with IMT measured in histological specimens. Thickening of the artery wall is a hallmark of atherosclerosis. It has thus been theorized that IMT measurements could aid in the prediction of cardiovascular disease (CVD) and thereby improve CVD prediction by traditional risk factors alone. However, recommendations regarding the use of carotid IMT for CVD risk prediction are conflicting. Several studies have shown an association between carotid IMT and future CVD events. The Kuoppio Ischaemic Heart Disease study showed 11% increased risk of myocardial infarction with each 0.1-mm incremental increase of carotid IMT. In the following years, several large clinical studies like the Atherosclerosis Risk In Communities study, the Cardiovascular Health Study, the Rotterdam Study, the Malm€o Diet and Cancer Study, and the Carotid Atherosclerosis Progression Study produced similar results. However, little or no additional prognostic value has been found by adding carotid IMT to a traditional risk factor score, such as the Framingham Risk Score (FRS). The contradictory results regarding the value of carotid IMT in CVD risk prediction is further portrayed by the conflicting results from 2 meta-analyses. Lorenz et al found the relative risks of CVD events increased by a factor of 1.15 for every 0.1-mm increase in carotid IMT, whereas Den Ruijter et al found no meaningful addition to CVD event prediction when carotid IMT was added to conventional risk prediction models. The conflicting results are also mirrored in diverging guideline recommendations. The 2010 American Heart Association/American College of Cardiology (AHA/ACC) guidelines recommended measurements of carotid IMT for CVD risk assessment in intermediate risk asymptomatic adults as a class IIa recommendation. The European Society of Hypertension/European Society of Cardiology recommends ultrasound scanning of the carotid arteries to detect vascular hypertrophy or atherosclerosis as a class IIa recommendation with level of evidence B. An update of the Mannheim Carotid Intima-Media Thickness and Plaque Consensus from the advisory board of the “Watching the Risk” symposium stated that measurements of carotid IMT and plaque presence are recommended for the initial detection of CVD risk in asymptomatic patients if at intermediate risk or if risk factors were present. However, in 2013, the AHA/ACC guidelines recommend against the use of carotid IMT for individual risk prediction in clinical practice. These varying study results and guideline recommendations are probably caused by differences in study design, specifically differences regarding carotid IMT measurements, such as measuring the common or internal segment and whether plaques are included or excluded from analyses, as commented in a review by Naqvi and Lee. Another hurdle when using carotid IMT for risk prediction is the large influence of age on IMT. In the current issue of Journal of the American Heart Association, Polak et al use an interesting approach to overcome this problem. Populationbased percentile values are commonly used to monitor growth in youth. They found that a similar approach, creating normative values for carotid IMT, was very suitable to compensate for the usually highly skewed distribution of the carotid IMT measurements and allow the generation of normative age-specific values. Using data from participants in The Multi-Ethnic Study of Atherosclerosis (MESA), they generated age-, sex-, and race-ethnic–specific normative values for carotid IMT and were thus able to compare 1 individual’s measurement as a percentile value, while taking age, sex, and race-ethnic differences into consideration. Their main hypothesis was that an approach using a combined normative percentile score from measurements of both the common and internal carotid artery IMT combined could The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association. From the Department of Medicine, Sørlandet Sykehus HF, Kristiansand, Norway. Correspondence to: Halvor Øygarden, MD, PhD, Department of Medicine, Sørlandet Sykehus HF, PB 416 Lundsiden, 4604 Kristiansand, Norway. E-mail: [email protected] J Am Heart Assoc. 2017;6:e005313. DOI: 10.1161/JAHA.116.005313. a 2017 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.