Imaging of subclinical atherosclerosis by B-mode ultrasound. Measurement reproducibility and assessment of atherosclerotic plaque occurrence, size and echogenicity in relation to cardiovascular disease

Abstract: Atherosclerosis is an insidious disease that in general has a very long clinical silent phase. This disease does not take place uniformly in the arterial tree, instead major sites for this disease process are the coronary arteries, carotid and cerebral arteries, aorta and the large arteries to the lower extremities. High resolution B-mode ultrasound technique has during the last two decades been used to non-invasively study the atherosclerotic process by measuring the thickness of the intima-media complex in the carotid and femoral arteries. By this technique it is also possible to assess occurrence, size and echogenicity of atherosclerotic plaques and also to determine atherosclerotic progression and to assess cardiovascular risk. Assessment of plaque echolucency in the carotid arteries has together with plaque size been shown to be associated with cerebrovascular events. Assessment of plaque echogenicity in the femoral artery has not been performed earlier.B-mode ultrasound was used to assess intima-media thickness, plaque occurrence and characteristics in initially helathy middle-aged men (n=391) as well as in high-risk hypertensive patients randomized to multiple risk factor intervention or usual care for 6 years (n=78 and n=79, respectively). The overall aim of the study was to improve the reproducibility of IMT measurements; to investigate if the occurrence or characteristics of non-stenotic carotid and femoral artery plaques may predict cardiovascular events; and also to assess the relationship between plaque characteristics and multiple risk factor intervention.The results showed that the interobserever errors in measurement of IMT can be decreased by using ultrasound images from both the right and left carotid arteries. This means that it will be possible to work with approximately 10% lower sample sizes in observational and interventional studies, at least for examination of the carotid arteries.Systolic blood pressure was significant predictors for both plaque occurrence in the carotid arteries and cardiovascular events during follow-up, even though there was no association between plaque occurrence at baseline and cardiovascular events. Furthermore, the presence of non-stenotic femoral artery plaques was predictive for future cardiovascular events. In addition, data also indicated that the risk of having a cardiovascular event was to a large extent confined to those with an echolucent plaque in the femoral artery at base line. However, due to the few echogenic plaques observed, the study did not have enough power to detect a difference in risk of cardiovascular events between the groups with echogenic and echolucent plaques, respectively. In hypertensive patients, data indicated that the beneficial effect of a multiple risk factor intervention was confined to those with echolucent plaques.