The topic of coronary calcium scores has come up more and more lately in the media, as studies are reported documenting their use.
Just what is a "coronary calcium score" and what does it mean?
First of all, atherosclerotic plaque is the material that, over the years, can accumulate in various arteries of the body, but especially coronary (heart) arteries, carotid (neck), aorta, and the large iliac and femoral arteries of the pelvis and legs.
During most of the 20th century, there was no easy, safe, and inexpensive method to identify atherosclerotic plaque and screen people for the potential for heart attack (coronary artery atherosclerosis), stroke, (carotid and aortic atherosclerosis), or abdominal aneurysms (aortic atherosclerosis). That's why attention focused on the concept of "risk factors," identifiable factors that increased the likelihood of having atherosclerosis and thereby potential for heart attack and its other manifestations.
Thus, smoking and high LDL cholesterol were among the risk factors that, when present, increased the likelihood of having atherosclerosis, especially coronary. While helpful, risk factors always suffered from a fundamental limitation: They did not represent the disease itself, only a potential contributor to its cause. In other words, if we have a 50-year old smoker, do we know whether or not she has coronary atherosclerotic plaque? We do not, though we know that she has higher likelihood than a 50-year old non-smoker. If a 42-year man has an LDL cholesterol of 160 mg/dl, can we decide that he has atherosclerotic plaque in his coronary or carotid arteries based on this value? Once again, no we cannot, though the statistical likelihood of having atherosclerosis in those arteries is greater than another 42-year man with LDL cholesterol of 120 mg/dl.
The quest to develop a screening tool not just for risk factors, but for the disease of atherosclerosis itself, has therefore been underway for several decades. If you have atherosclerotic plaque, you have the disease. If you have a little bit, you have less potential for stroke or heart attack compared to someone with a lot. Thus, quantification is an important aspect of atherosclerosis detection.
That's where coronary calcium scores come in. Of all the ingredients contained in atherosclerotic tissue-inflammatory cells, cholesterol and other fats, structural tissue, and calcium-it's the calcium that can be readily visualized in the coronary arteries. It can also be quantified.
Dr. John Rumberger, while at the Mayo Clinic in the 1990s, made a crucial observation. He determined that, while the presence of calcium up until then had been considered nothing more than a curiosity, even an annoyance since it sometimes got in the way when performing procedures like stent implantation, calcium was present in a reasonably consistent proportion to the other components of plaque, always occupying 20% of the volume. (He and his team determined this by examining coronary arteries of people who had died.) In other words, measuring 2 mm3 of calcium meant that there was 10 mm3 of total atherosclerotic tissue.
Dr. Rumberger took the idea further and found that, using then new technology of electron-beam tomography (EBT), also called ultra-fast CT, the calcium in the moving arteries of the heart could be visualized and precisely measured. By quantifying calcium, he could indirectly quantify total coronary atherosclerotic plaque.
It wasn't until Dr. Arthur Agatston of Miami, Florida, better known more recently for authoring The South Beach Diet, developed a simple method of "scoring" coronary calcium. This permitted a standardized method to measure calcium, so that coronary calcium measured in Miami would be measured the same way as in New York or London. Dr. Agatston's system was based on measuring the area of calcium multiplied by a measure of the density of calcium.
While, over the years, efforts have been made to improve on Dr. Agatston's simple system (e.g., measure volume, rather than area, or measure the mass of calcium), the "Agatston score" has survived the test of time and remains the most popular and widely used method for quantifying coronary calcium and, thereby, coronary atherosclerotic plaque.
Since the early efforts of Drs. Rumberger and Agatston, literally thousands of research studies, big and small, have been performed to better understand how this simple coronary calcium score can be used to best advantage. The original EBT technology has also been largely replaced by a similar technology called multidetector CT.
Based on the clinical studies performed to date, several simple observations about coronary calcium score can be made:
- The higher the coronary calcium score, the greater the potential for heart attack. Thus, a person with a score of zero has extremely low risk over, say, five years, while a person with a score of 1000 or greater has up to 20% annual risk.
- Coronary calcium scores increase if no preventive action is taken. The average rate of increase, in fact, is 30% per year (though can differ widely from individual to individual).
- The more the coronary calcium score increases, the greater the likelihood of heart attack or the appearance of symptoms of heart disease, like chest pain.
- Coronary calcium scores improve the prediction of heart attack over and above standard risk factors like LDL cholesterol.
After this, however, the data become somewhat confusing. Several studies, for instance, determined that statin cholesterol drugs failed to substantially slow the rate of increase in coronary calcium scores. Rather than asking why and searching for alternative explanations (vitamin D deficiency), this caused many researchers to simply dismiss the value of coronary calcium scoring because it didn't do what they expected when statin drugs were taken.
Coronary calcium scores are proving to be like mammograms are to women in screening for breast cancer: a simple, low-cost, test that requires a modest quantity of radiation exposure (approximately equivalent to 2 mammograms).
Next: What to do if you have a "positive" heart scan score