Abstract 689: Effect of the Cardiac Cycle on Carotid Intima-media Thickness (IMT) Measurements: The Multi-ethnic Study of Atherosclerosis
Introduction: Common carotid artery (CCA) intima-media thickness (IMT) is a measure of subclinical cardiovascular disease. Small studies have suggested that an inverse relationship exists between IMT and the artery diameter during the cardiac cycle. The epidemiological and clinical implications of this observation have not been rigorously studied.
Materials and methods: Far wall IMT of the right CCA was measured at mechanical end-diastole (ED) and end-systole (ES) on ultrasound studies of 5633 of the 6814 members of the Multi-Ethnic Study of Atherosclerosis (MESA). These members of the MESA IMT progression study consisted of 52% females, 22% Hispanics, 26% Blacks, 12% Chinese and 40% whites. Multivariable regression models were generated with ED-IMT, ES-IMT and change in IMT during the cardiac cycle as dependent variables and traditional cardiovascular risk factors as independent variables.
Results: The average age of our population was 61.9 years (45 to 84 years). Mean ED-IMT and ES-IMT were 0.68±0.19 and 0.64±0.18 mm (std dev). Average change in carotid IMT during the cardiac cycle was 0.041 mm (95% CI: 0.039 – 0.042 mm). In a fully adjusted model, change in carotid IMT during the cardiac cycle was associated with pulse pressure (p < 0.0001) and no other traditional risk factors (outside of age, race, and gender). An ethnic difference was noted in Chinese and Hispanics who had less of a change in IMT as compared to whites. Overall, ED-IMT was more strongly associated with risk factors than ES-IMT (change in explained variability of 0.69%).
Conclusion: Measurable differences in carotid IMT are seen during the cardiac cycle. This effect should be accounted for when IMT is used for risk assessment of subclinical disease and as an outcome in intervention trials. The observed difference in IMT corresponds to a difference expected for an age difference of 3 to 6 years.