Coronary Artery Calcium Score vs. Coronary CT Angiogram: What They Are and What They Show

What is a coronary artery calcium scan (CACS)?

A CACS is a simple CT of the heart performed without injection of any contrast dyes that permits the easy identification of calcification (plaque) in the three major heart arteries. There are no needles used, no pain, and no risk to your kidneys.

By good fortune, the density of arteries is different than the fat they sit in and the muscle and blood that are nearby in the heart. Calcium comprises about 20 percent of plaque in arteries but is such a different density than the rest of the heart that even small amounts show up like a beacon of aging and damage in by just holding your breath for 10 seconds.

A software program permits a calculation, called the Agatson score, to be determined after the scan. If there is no calcium in the coronary arteries, the score is zero. Alternatively, even in persons with NO symptoms, the score can be in the tens, hundreds and even thousands indicating small to huge amounts of calcified heart artery plaque that can lead to symptoms, sudden heart attacks, or sudden deaths. The highest CACS I have seen was over 6,000!

Research studies indicate that the heart calcium score is the most available way to detect silent heart disease and also a strong predictor of future cardiac events like heart attack and death. In Detroit, for example, the scan costs as little as $75 so this is not just a test for the wealthy.

If you have not heard of a CACS it may be because it has not been promoted as much as more expensive and invasive stress tests and heart catheterizations that expose you to much more radiation, sometimes 10–15 times the amount of the CACS. These other tests can cost from $1,000 to $10,000 or more. The underuse of CACS is the focus of a provocative and “must watch” documentary called The Widowmaker. Although you may need a prescription from your health care provider, I am quite certain that after watching this documentary, you will conclude that you must know your CACS. I know mine and it is zero.

What about the possibility that arteries have plaque but that it is not calcified and missed by the CACS?

There are two drawbacks to the CACS. The reports do not indicate the % of narrowing in the arteries as this cannot be measured. The CACS also does not detect "soft" non-calcified plaque that is almost in the arteries if calcification is found (a CACS of > zero).

A study addressed this in a large number of patients with chest pain (not asymptomatic) whom had both the basic CACS and also had the more advanced CT study that involves injecting dye (coronary CT angiography or CCTA). (I do NOT consider a CCTA a screening test for most asymptomatic person due to the risk of allergy and kidney reaction to the contrast agent administered along with the cost ($500-1500). However, some patients want all the data and CCTA is chosen after a full conversation of risks and benefits).

Returning to the study, the authors wrote:  "In this prospective cohort study, consecutive patients with stable chest pain underwent CCTA as part of routine clinical care over 7 years. Major adverse cardiac event (MACE) was defined as cardiac death, non-fatal myocardial infarction and/or non-elective revascularization. Of the 751 (82%) patients with a zero CAC in whom CTCA was performed, 674 (90%) had normal coronary arteries free of all blockages. This is even though they had some chest pains. Of the remainder, 8% had minor non-calcified CAD with < 50% stenosis and 2% had ≥ 50% narrowing in at least one coronary artery. The “negative predictive value” of a zero CACS for excluding a ≥ 50% narrowing was 98.1%.

Over a follow-up period of 2.2 years (range 1.0–7.0 years), the absolute annualized rates of MACE were as follows: for a zero CACS it was 1.9 per 1000 person-years and non-zero CAC 7.4 per 1000 person-years (HR 3.8, p = 0.009). After adjusting for age, gender and cardiovascular risk factors, the hazard ratio (a statistical measure of the amount of increased risk) for all-cause mortality among the zero CACS group vs. the non-zero CACS was 2X.

THE AUTHORS CONCLUDED THAT:

A zero CACS score in patients undergoing CT scanning for suspected stable angina has a high negative predictive value for the exclusion of obstructive CAD and is associated with a good medium-term prognosis.

What Should You Consider?

Whether you have ever had symptoms suspicious for heart disease or not, a CACS of zero buys you 98% peace of mind for a few years at least according to this study. This is far in excess of stress tests which may be 85% accurate, expose you to much more radiation, and cost 10–15 times more.

I generally recommend the basic CACS scan to patients with no history of coronary disease (no stent, bypass, heart attack, prior cardiac catheterization show plaque). If the score is abnormal, I generally do not recommend repeating the CACS in the future as there is no convincing data the CACS can be reduced (although soft plaque can be reduced) and the need for intensive therapy is clear. If a repeat CT is done in a patient with an abnormal CACS, I strongly recommend the CCTA, not the CACS, to get the extra information (percent narrowing and amount of soft plaque).

A new option is to use artificial intelligence (AI) to interpret the CCTA for the most precise measurements offered by Cleerly Health. We have a referral relationship with them and dozens of patients have had that advanced AI scan interpretation.

In those with a CACS of Zero, the best outcome, a repeat CACS is considered in 5-7 years to see if the score stayed zero (a good outcome) or has progressed to calcified coronary arteries. 

FYI, I have had a CACS of zero at age 40, 50 and 60. I will let you know at age 70 if I do another but that is a number of years away!