Ultrasound measurement of carotid plaque as a surrogate outcome for coronary artery disease

Intima-media thickness (IMT) is commonly used as a surrogate marker for coronary artery disease (CAD). However, use of this parameter is a problem because (1) it assumes uniform thickness throughout the blood vessel, and (2) it detects changes primarily in the media, whereas atherosclerosis is a focal phenomenon that is confined to the intima. As an alternative to IMT, we have investigated the use of ultrasound measurements of plaque area and plaque volume as surrogate outcomes for CAD. Plaque area is a sensitive predictor of coronary disease progression and is closely associated with CAD. Clinical studies have shown that the sample size needed to detect atherosclerosis progression is sufficiently small to make this a useful assessment in clinical trials. Plaque volume, as measured by 3-dimensional ultrasound, may offer an even better means of assessing atherosclerosis. Plaque volume assessments are highly accurate and the data can be saved on a compact disc for central reading. Because of the high degree of accuracy and the increased size of plaque volume relative to plaque area or IMT, it is likely that only a small sample size will be required to detect clinically meaningful differences in plaque volume in a clinical trial.