Preventive cardiologists have a wonderful tool for noninvasively identifying plaque (atherosclerosis) in the arteries to the heart: the coronary artery calcium (CAC) scan.
Since 1/3 of Americans die from atherosclerotic cardiovascular disease (ASCVD) -- mostly heart attacks and strokes -- and dropping dead is often the first symptom of ASCVD, it is incredibly important to identify early, "subclinical" ASCVD and begin measures to reduce risk.
How early to begin that process is open to debate. The sudden death of the 41-year-old son of a patient of mine, reinforced to me how crucial it is to begin risk assessment and potential treatments as early as possible, especially in individuals with a strong family history of premature ASCVD.
We use standard risk factors like lipids, smoking, age, gender, and diabetes to stratify individuals according to their 10-year risk of heart attack and stroke (using this online risk calculator). However, many apparent low-risk individuals (often due to inherited familial risk) drop dead from ASCVD and many apparent high-risk individuals have no subclinical ASCVD and don't need preventive therapy.
I've been utilizing CAC (also termed "heart scan," "coronary calcium score," or "cardioscan") to help assess my patients' risk of ASCVD for years, though the procedure is not covered by insurance and, until recently, was not strongly endorsed by major guidelines.
The CAC can help in deciding who needs more aggressive treatment
Below is an actual CAC on a patient of mine.
Heavy calcium deposits (indicating advanced premature subclinical atherosclerosis and conferring a very high risk of heart attack and stroke) are observed in the left anterior descending coronary artery in an asymptomatic 45-year-old man.
The CAC is an outstanding tool for further refining the risk of heart attack and stroke and helping better determine who needs to take statins or undergo aggressive lifestyle reduction.
This is particularly important for patients who have many reservations about statins or who are "on the fence" about taking them when standard risk factor calculations suggest they would benefit.
In late 2018, I noted that CAC had been embraced by major guidelines:
For those patients aged 40-75 without known ASCVD whose 10 year risk of stroke and heart attack is between 7.5% and 20% (intermediate, see here on using risk estimator) the guidelines recommend "consider measuring CAC."
If the score is zero, for most consider no statin. If score >100 and/or >75th percentile, statin therapy should be started.
But what about the individual who has a strong family history of premature CAD and is, say, 35 or 39 years of age. Do we ignore advanced risk assessment? Very few individuals die in their 30s from ASCVD but I have a number of patients who suffered heart attacks in their 40s.
The Importance of Being Proactive With Your Cardiovascular Health
First, it's never too early to start thinking about your risk of cardiovascular disease. I have been using CAC more frequently in the last five years in individuals <40 years with a strong family of early sudden death or heart attack and often we find very abnormal values (see my discussion on CAC in the youngish and a combined imaging and biomarker approach).
In addition, the earlier we can start risk modification, the better as the process begins very early in life and accumulates over time.
The Coronary Artery Risk Development in Young Adults (CARDIA) Study, published in 2017, has demonstrated the early development of a nonzero CAC score in the youngish and the predictive value of the high CAC score for mid-life ASCVD events. It was a prospective community-based study that recruited 5,115 Black and white participants age 18 to 30 years from March 25, 1985, to June 7, 1986. The cohort has been under surveillance for 30 years, with CAC measured 15 (n=3,043), 20 (n=3,141), and 25 (n=3,189) years after recruitment. The mean follow-up period for incident events was 12.5 years.
The conclusions:
Any CAC in early adult life, even in those with very low scores, indicates significant risk of having and possibly dying of a myocardial infarction during the next decade beyond standard risk factors and identifies an individual at particularly elevated risk for coronary heart disease for whom aggressive prevention is likely warranted.
If heart disease runs in your family or you have any of the "risk-enhancing" factors listed above, consider a CAC, nontraditional lipid/biomarkers, or vascular screening to better determine where you stand and what you can do about it.
Included in my discussions with my patients with premature ASCVD is a strong recommendation to encourage their brothers, sisters, and children to undergo a thoughtful assessment for ASCVD risk.
There is ample support for making CAC a part of such assessment.
Hopefully, very soon, CMS and the health insurance companies will begin reimbursement for CAC. As it currently stands, however, the $125 you will spend for the test at my hospital is money well spent.
If you want to be proactive about the cardiovascular health of yourself or a loved one, download the MESA app and evaluate your risk. Ask your doctor if a CAC scan will help refine that risk further.
More Questions and Answers on CAC
There are many other questions to answer with regard to CAC:
Should they be repeated?
If non-zero, I say no. If zero, I say yes, in 2-4 years. Findings from the MESA (Multi-Ethnic Study of Atherosclerosis) study (mean age 58 ± 9 years, 63% women, mean 10-year atherosclerotic cardiovascular disease risk 14 ± 13%) in patients with an initial zero CAC showed that the prevalence of CAC >0 increased with time, from 11% at 2 years to 50% at 10 years. Using a testing yield of 25% (number needed to scan of 4 to detect CAC >0), the estimated time period to CAC conversion of low, intermediate, and high estimated risk men was 7, 4, and 3 years, respectively, and for women was 8, 5, and 3 years, respectively.
Do statins influence the score?
Yes. CAC score may actually be higher on statins than if you were not. This is because calcium is taken up into plaques as they "heal" or progress from active/inflamed/likely to rupture to scarred and quiescent.
Will I benefit from a CAC if I have had a coronary stent/coronary bypass surgery or other clinical event due to advanced ASCVD?
No. We are going to treat you aggressively no matter what the CAC shows in this situation.
Is there information in the scan beyond just the score that is important?
Yes. The standard method of quantifying CAC from noncontrast cardiac-gated CT scans is the Agatston score. The Agatston method, which up-weights the area of calcified plaque for greater calcium density, assumes that both the area and density of calcified plaques are positively related to ASCVD events. However, MESA has shown that CAC density was inversely associated with incident CVD events.
Is a scan helpful after a normal stress test?
It can be because stress tests are designed to identify tightly blocked coronary arteries. You can have loads of atherosclerotic plaque lining your arteries and have a totally normal stress test.
Should all patients with a high coronary calcium score undergo stress testing?
I now believe the answer to this is no. If the patient has symptoms suggestive of angina or ischemia then stress testing or coronary CT angiography is appropriate.
Doesn't CAC scanning miss early, soft plaque which can be easily identified on a coronary CT angiogram (CCTA)?
Yes, it does. The CCTA gives us a complete picture of the coronary arteries including soft and calcified plaque along with a good estimate of the degree of narrowing of the arteries. However, a CCTA does not work well for screening purposes because:
- It's expensive (typically >$800 out of pocket cost vs around $100 for CAC)
- It uses much higher radiation doses (3-8 mSv vs 1 mSv for CAC)
- IV contrast is needed
Like most things in cardiology we have a lot to learn about CAC. There are many more studies to perform. Many questions yet to be answered.
A study showing improved outcomes using CAC-guided therapy versus non-CAC-guided therapy would be nice. However, due to the long time and thousands of patients necessary, it is unlikely we will have results within a decade.
We can blame a lot of heart disease on lifestyle: poor diets and lack of exercise are huge factors leading to obesity, diabetes, hypertension, and hyperlipidemia, but in many patients I see who develop heart disease at an early age, lifestyle is not the issue, it is the genetic cards that they have been dealt.
Until we develop reliable genetic methods for identifying all those at high risk, it makes sense to utilize methods such as vascular screening or coronary calcium to look for atherosclerosis in individuals with a family history of premature CAD.
The earlier we start looking, the earlier we can intervene and lower the slow and progressive build up of atherosclerotic plaque in the arterial beds.
Given that we have extremely safe and effective medications that can help individuals dramatically reduce their lifelong risk of heart attack, it makes sense to look early and intervene accordingly.
I don't want to wait a decade to start aggressively identifying who of my patients is at high risk for sudden death, heart attack, or stroke.
Anthony C. Pearson, MD, is a noninvasive cardiologist and professor of medicine at St. Louis University School of Medicine. He blogs on nutrition, cardiac testing, quackery, and other things worthy of skepticism at The Skeptical Cardiologist, where a version of this post first appeared.