This article was originally posted in the Montreal Gazette.
Read enough radiology reports and eventually you will find one that mentions calcifications in the heart or the aorta. When it appears in black and white, it sounds worrisome and can generate an emergency referral. But both patients and referring physicians are usually surprised to learn that the finding is not quite as dangerous as it sounds.
Unfortunately, as we age, plaque accumulates in our arteries. This starts as soft, cholesterol-laden plaque that eventually calcifies and hardens. Even though the process effectively begins at birth, most people do not have clinically significant blockages in their arteries until they are well into middle age.
Interestingly, and somewhat counterintuitively, calcified plaque is probably the less dangerous of the two. When a heart attack happens it is due to the sudden rupture of a soft, unstable plaque that might be obstructing only 10 or 20 per cent of the artery. Longstanding, calcified 90-per-cent blockages don’t cause heart attacks. They may cause angina — chest pain on exertion — but a stable plaque won’t suddenly rupture and provoke a myocardial infarction.
Thus, you might wonder why we should care about calcium in our arteries at all. Coronary artery calcium (CAC) testing is potentially useful for patient care. It’s just not useful for diagnosis. It’s useful for prognosis.
The problem with CAC is that most people conflate the calcium score with a coronary CT scan. The confusion is understandable since both tests are done with a CT machine and are often done at the same time.
A coronary CT is a more involved scan that requires intravenous injection of contrast dye to diagnose blocked arteries. Measuring CAC is done with a quicker, simpler scan that requires no contrast and just looks for calcium accumulation in the arteries of the heart.
For practical and logistical reasons, the two tests are often done simultaneously as the patient is “already in the machine” but we often forget that the tests provide complementary pieces of information. A coronary CT scan is a non-invasive way to diagnose a potentially blocked artery. Getting a CAC score tells you something different. It tells you if someone needs to be treated more aggressively.
The general purpose of measuring someone’s coronary artery calcium is to decide whether to treat their risk factors. For example, if you were on the fence about whether you wanted to start someone on blood pressure medication or treat their high cholesterol, then a high calcium score might push you to treat, whereas a low calcium score wouldn’t. CAC score performs better than some other blood markers that have been proposed over the years, and it does help better identify high-risk patients who would benefit from prophylactic treatment.
I’ve personally always been a bit less enthusiastic about sending patients for CAC scores. Although to be fair, by the time a patient gets to me they’ve likely already been identified as high risk, which makes the value of the test is moot. Its primary purpose is for risk refinement in intermediate-risk patients. Very low-risk and very high-risk patients don’t benefit much from the test because you won’t treat them or will continue to treat them regardless of the result. And while CAC scores are fairly easy to do with little major downside, they cost money, use up medical resources and scanner time that could be used for more urgent cases and expose patients to an admittedly small dose of radiation that could otherwise be avoided.
Occasionally, coronary calcifications will be seen on non-cardiac CT scans. A patient may get a lung scan because of a nodule seen on an X-ray and the report will comment on coronary calcifications. This is increasingly common but shouldn’t be seen with any additional worry. CAC, whether measured deliberately or seen incidentally, has the same prognostic value. It lets you fine tune patient’s preventative cardiac care. It shouldn’t be a cause for alarm.