Ultrasound B-mode imaging in observational studies of atherosclerotic progression

Investigations of the progression of atherosclerosis in human arteries suggest that changes in the thickness of the arterial intima-media complex, observable with B-mode ultrasonography, may precede development of atherosclerotic lesions. For epidemiological studies and clinical trials, B-mode ultrasound has the advantage that it is noninvasive, can be used in nonsymptomatic subjects, and can be carried out repeatedly, thus reducing the necessary sample size. In the Kuopio Ischaemic Heart Disease Risk Factor Study, we have assessed the reliability of B-mode ultrasound through studying intraobserver and interobserver variability. We have also investigated its predictive value by associating ultrasound observations with clinical end points, risk factors for common carotid and femoral atherosclerosis, and predictors of progression of common carotid atherosclerosis.

The study of B-mode ultrasound reliability was conducted in 10 middle-aged men, with initial and two repeat scannings. The between-observer coefficient of variation was 10.5% for the first assessments by four observers. The intraobserver variability, described as the mean of the absolute difference between the first and third observations, was 0.087 mm, or 8.3% of the mean intimal-medial thickness (IMT). Ultrasonographic assessment of 1,257 men was compared with diagnostic information obtained from a prospective registry for acute myocardial infarction (AMI). The presence of any atherosclerotic findings was associated with a 3.0-fold risk of AMI. For each 0.1 mm of common carotid IMT, AMI risk increased by 11% (p < 0.001). Common carotid artery and femoral artery atherosclerosis, as assessed by mean maximal IMT, had different risk factor profiles. Age, serum low density lipoprotein cholesterol, smoking, platelet aggregability, serum copper, serum selenium (inversely), and blood hemoglobin were the strongest predictors of 2-year increase of common carotid IMT.

On the basis of our experience and findings, the ultrasonographic assessment of common carotid atherosclerosis appears to be a feasible, reliable, valid, and cost-effective method for both population studies and clinical trials of atherosclerosis progression and regression.