Variations in Common Carotid Artery Intima-Media Thickness during the Cardiac Cycle: Implications for Cardiovascular Risk Assessment

Abstract

Common carotid artery intima-media thickness (IMT), a measure of atherosclerosis, varies between peak systole and end-diastole. This difference might affect cardiovascular risk assessment. IMT measurements of the right and left common carotid arteries were synchronized with an electrocardiogram, using the R wave for end-diastole and the T wave for peak systole. IMT was measured in 2,930 members of the Framingham Offspring Study. Multivariate regression models were generated with end-diastolic IMT, peak systolic IMT, and change in IMT as dependent variables and Framingham risk factors as independent variables. End-diastolic IMT estimates were compared with the upper quartile of IMT on the basis of normative data obtained at peak systole. The average age of the study population was 57.9 years. The average difference in IMT during the cardiac cycle was 0.037 mm (95% confidence interval, 0.035-0.038 mm). End-diastolic IMT and peak systolic IMT had similar associations with Framingham risk factors (total R(2) = 0.292 vs 0.275) and were significantly associated with all risk factors. In a fully adjusted multivariate model, thinner IMT at peak systole was associated with pulse pressure (P < .0001), low-density lipoprotein cholesterol (P = .0064), age (P = .046), and no other risk factors. Performing end-diastolic IMT measurements while using upper quartile peak systolic IMT normative data led to inappropriately increasing by 42.1% the number of individuals in the fourth IMT quartile (high cardiovascular risk category). The difference in IMT between peak systole and end diastole is associated with pulse pressure, low-density lipoprotein cholesterol, and age. In this study, the mean IMT difference during the cardiac cycle led to an overestimation by 42.1% of individuals at high risk for cardiovascular disease.