As a heart surgeon, I think I have a unique perspective on coronary artery disease as I have seen and felt literally thousands of heart arteries. The difference between a heart surgeon (cardiothoracic surgeon) and a cardiologist is often confusing to many people. Basically, a cardiac surgeon opens up the chest and feels the coronary arteries in order to do a coronary artery bypass procedure (CABG) and a cardiologist relies on imaging to do angioplasty and stenting .
I also think it is important to say one thing about coronary artery atherosclerotic disease. Contrary to popular belief, when narrowing of the artery occurs, it occurs from inside the artery wall and pushes the inner layer called the intima inwards narrowing the artery. In other words, the cholesterol plaques do not start in the surface of the artery where the blood flows which is called the lumen. Early plaques, which are most prone to rupture, contain little or no calcium. As the plaque matures, it may acquire calcium. Think of it in the context of how bone develops. A young child has soft bones that are more pliable and less prone to fractures as compared to adult bones that are most rigid, calcified and more prone to breaking. The cholesterol must be driven into the artery walls in what are called lipoproteins. That is why I measure LDL-P, which are the cars which “traffic” the cholesterol into the artery wall. The best way to slow the progression of the plaque development is to dramatically lower one’s LDL-P.
Now with these facts out of the way, we can talk about using CT scan to assess the amount of calcium in the atherosclerotic plaques in the artery. This is called Coronary Artery Calcium Scoring (CAC). This is NOT a way to identify blockages in the artery. It is only a way to assess if there is coronary atherosclerosis. Like I said earlier, many plaques have little or no calcium which then would be interpreted as normal. In 2007, the American College of Cardiology and American Heart Association published a “Clinical Consensus Document on Coronary Artery Calcium Scoring Using Computerized Tomography”. This paper was extremely thorough and gave final recommendations when this modality should be used.
When patients are evaluated as to risk of future cardiovascular events, they are stratified into low risk, moderate risk, and high risk. Low risk being a 0-10% chance over a 10 year period, moderate risk 10-20% and high risk being 20% or greater. According to the expert committee, the only group may be considered for CAC scoring is the intermediate risk group. I will include the exact quote:
“The Committee judged that it may be reasonable to consider use of CAC measurement in such patients based on available evidence that demonstrates incremental risk prediction information in this selected (intermediate risk) patient group. This conclusion is based on the possibility that such patient might be reclassified to a higher risk status based onhigh CAC score, and subsequent patient management may be modified”. In addition, “CAC data are strongest for Caucasian, non-Hispanicmen. The Committee recommends caution in extrapolating CAC data derived from studies in white mento women and to ethnic minorities”.
To summarize, measurement of CAC for cardiovascular risk assessment in selected asymptomatic adults ≥40 years of age at intermediate risk can be considered as a one time test if the presence of calcium would modify the current treatment for elevated cholesterol.
Since that time, thousands of scans have been performed. The majority of the scans have been done for no clear reason and have not followed current guidelines, which have not really changed since 2007.