Ultrasound measurements of subclinical carotid atherosclerosis : methodological and clinical studies

Abstract: Ultrasound measurements of subclinical carotid atherosclerosis have been evaluated as an additional parameter in risk evaluation of cardiovascular diseases (CVD). The overall aim of this thesis was to increase knowledge regarding ultrasound measurements of subclinical carotid atherosclerosis. This included methodological studies of the reproducibility in commonly applied measurements and evaluation of subclinical carotid atherosclerotic progression. All studies within this thesis are based on material from the population based, randomized control trial VIPVIZA. Enrolled from a routine CVD prevention programme, all participants had an additional carotid ultrasound examination including measurements of carotid intima media thickness (cIMT) and carotid plaque detection. The group randomised to the intervention received a pictorial presentation which illustrating their individually measured subclinical atherosclerotic burden. At the 3-year follow-up the same measurements were repeated.Variability, defined by variation of coefficient (CV) of measurements, of plaque risk markers including echogenicity and plaque area were evaluated throughout the cardiac cycle. Additionally, the inter-observer reproducibility of plaque detection was evaluated, and the intervention effect on the 3-year cIMT and plaque progression was compared between intervention (n: 1575)  and control group (n: 1579). Lastly, association of baseline carotid wall echogenicity and the 3-year progression of cIMT was evaluated. Small and echolucent plaques had higher CV in measurements of area and echogenicity, respectively. Cardiac cycle variations caused reclassification of up to one in four of the analysed plaques. Small carotid plaques contributed to decreased inter-sonographer reproducibility as compared to large plaques. In the 3-year follow-up the intervention group showed decreased progression of cIMT in the left carotid compared to the control group. No difference was found for in plaque related variables. The echogenicity of the carotid wall associated with the progression of cIMT over the 3-year follow-up period, where echolucent carotid wall had a higher rate of progression bilaterally.Variability of plaque risk markers and the reproducibility of plaque detection should be considered in analysis of subclinical carotid atherosclerosis by ultrasound. Progression of left cIMT was decreased by the intervention, which indicates that increased preventive actions were taken by the intervention group. The echogenicity of the carotid wall may contribute new insights regarding identification of progressive atherosclerotic diseases.