What is the accuracy of carotid artery ultrasound to detect heart problems?

Depends. Some studies suggest that by using carotid duplex and measuring intima media thickness we can detect early coronary artery disease with sensitivity of 85% but low specificity of 39%. It is a good screening test that is not invasive but not very accurate.
Coronary calcium. Coronary calcium screening is the definitive test for noninvasive detection of CAD in men over 40 & women over 50 with any risk factor. I use cimt in younger patients. There is much more predictive & outcome data in ccs.
Good. We have accepted "carotid artery intimal thickness" as a surrogate for coronary artery health. I'm not sure I am totally aboard but this is generally accepted as a measure of the condition of the heart arteries. If we find the carotids to be ill it seems reasonable the coronaries are similarly affected. Treat aggressively to lower cholesterol and lower other risk factors.