A coronary calcium computed tomography (CT) scan or CAC (coronary artery calcium) test is one of the best screening methods for CHD (coronary heart disease) which is also known as coronary artery disease or ischemic heart disease. CHD is a disease which causes buildup of plaque (atherosclerosis) in the coronary arteries which supply blood to the heart. Because this disease is the most common type of heart disease and is the reason heart attacks occur, a diagnostic method that can predict the onset and likelihood of a cardiovascular event may be a life-saver.
What a CAC test is and why get it
To understand why the CAC test is important we must first look at the statistics. CHD is the number 1 cause of deaths annually. In 2013, 8.14 million people died as a result of CHD worldwide.
It is caused by chronic inflammation of the arterial wall which causes cells to clump up and narrow the coronary arteries. Calcification is frequently associated with this plaque buildup and as time goes on, can harden, hence –sclerosis (from Greek means “hardening”). If the obstruction of the coronary artery reaches a certain stage, it can trigger a cardiovascular event, but the question is, can we predict such things?
A CAC scan, also known as an electron-beam CT or a multi-detector CT can show calcium in artery walls, which stands out from surrounding tissue as white spots or streaks. The advantage over other methods that aim to evaluate the coronary arteries is speed, precision and noninvasiveness. Another major advantage is that the test is standardized, as it uses software to quantify the amount of calcium in the coronary arteries, deriving a calcium, or Agatston score. Researchers have been able to show a direct correlation between your calcium score and the likelihood of cardiovascular events.
Severe calcification of the left anterior descending coronary artery (red arrow), the portion of the circumflex coronary artery within the imaging plane (white arrow), and the aortic root around the origin of the left main coronary artery (yellow arrow).
Weighing the risks and making decisions
The apparent link between calcium scores and mortality isn’t something new. There have been several major studies looking into this connection. One study, that reviewed 25,253 individuals who had no symptoms found that the adjusted 10 year survival rate for persons with a score of 0 was 99.4% and those with a score of >1000, 87.8%. These are obviously two extremes, but the study was also able to identify relative risk ratios: 2.2-, 4.5-, 6.4-, 9.2-, 10.4-, and 12.5-fold for scores of 11 to 100, 101 to 299, 300 to 399, 400 to 699, 700 to 999, and >1,000, respectively.
A more recent study examining almost 10,000 patients with a longer 15 year follow-up period found similar results.
So, what can increase the risk for CAD, and what can we do about it? From the studies mentioned above, scientists can make the conclusion that age and calcium score are the top factors for all-cause mortality. Other factors include hypertension, dyslipidemia, diabetes, being a current smoker, and a family history of coronary heart disease.
What we can get from this simple test, which is cost-effective and highly accurate, is an indication of whether the patient requires some sort of preventive measures, such as statin and aspirin therapy not to mention the obvious lifestyle changes.
Currently, the American Heart Association and the American College of Radiology recommend CAC scans be considered for individuals with low-to-intermediate or intermediate risk for cardiovascular disease if a physician is on the fence about prescribing lifelong medication. In other words, if you have no known risk factors, there is no reason to get a CAC scan, and conversely, if you have been diagnosed with heart disease or have had a cardiovascular event in the past, you should already be taking medication.
Some might say that a drawback of the CAC test is that not all plaques are calcified. This is of course, true, but not all patients, or rather, not all insurance companies will cover a full CT angiogram if there are no symptoms.
There has recently been strong interest in a new method of scoring lesions, lesion-specific calcium score. This concept takes into account each lesion, measuring its width, length, density and distance for major coronary arteries. The developers of this new technique have published studies and have patented this method, which may be superior to the Agatston score. As other researchers confirm the efficacy of lesion-specific calcium score, it may soon phase out Agatston scoring as the go-to method for quantifying calcium in atherosclerotic lesions.
Budoff MJ, Shaw LJ, Liu ST, et al. Long-Term Prognosis Associated With Coronary Calcification: Observations From a Registry of 25,253 Patients. J Am Coll Cardiol. 2007;49(18):1860-1870.
GBD 2013 Mortality and Causes of Death Collaborators. (2015). Global, regional, and national age-sex specific all-cause and cause-specific mortality for 240 causes of death, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet, 385(9963), 117–171.
Finegold, J. A., Asaria, P., & Francis, D. P. (2013). Mortality from ischaemic heart disease by country, region, and age: Statistics from World Health Organisation and United Nations. International Journal of Cardiology, 168(2), 934–945. http://doi.org/10.1016/j.ijcard.2012.10.046