This Artery Screening Tool Detects Early Signs of Dangerous Heart Disease
The test uses CT scans to find calcium buildup in arteries
Preventive medicine can be messy. In a perfect world, we’d put helmets only on motorcyclists who we knew were going to crash. And we’d only do mammograms on women we knew were going to get breast cancer. But things are hardly perfect, and when it comes to heart disease — the leading cause of death in our country — early treatment of risk factors is particularly important.
That’s because for too many patients, the first warning that they have coronary artery disease is when the paramedics arrive to pull the proverbial elephant off their chest.
We've seen one high-profile example of heart disease in the news recently, with Democratic presidential hopeful Sen. Bernie Sanders undergoing heart surgery Tuesday to remedy a blocked artery. Two stents were placed in his artery to successfully relieve the blockage.
Heart Disease: A Gradual, Dangerous Progression
At the hospital where I work, more than 70% of patients arriving for an emergency intervention for a serious heart attack had not been previously diagnosed with heart disease.
Although heart attacks arrive acutely and often without warning, the disease process leading up to it is generally a much slower and chronic one. On an anatomical level, a heart attack is caused by an arterial blockage that starves the heart muscle of blood flow and oxygen.
"It's, basically, the only test we have that trumps age in terms of its ability to predict cardiovascular mortality."
In most cases, that blockage is due to atherosclerosis — a scarring of the blood vessels due to inflammation and damage caused by high blood pressure, smoking, bad cholesterol, diabetes or genetic/family history factors that we are trying to understand better.
If those risk factors are not controlled, the scarring progresses over time and arteries become increasingly narrow. Eventually, calcium gets deposited within the atherosclerotic scar. Like graying hair, calcium is a marker for “maturing” atherosclerosis. X-rays don’t penetrate calcium deposits very well, so on a computerized tomography (CT) scan or X-ray, diseased arteries and healthy bones both look white.
Using CT Scans to Screen for Artery Blockage
Coronary Artery Calcium (CAC) screening uses CT scans to determine whether arteries are blocked. It’s not a new test, but it is increasingly being recognized as an important tool in defining which patients have more advanced atherosclerotic cardiovascular disease (ASCVD) and are at the highest risk of having a stroke or heart attack.
In April, the American College of Cardiology/American Heart Association issued updated guidelines recommending CAC testing to those with borderline or intermediate risk of ASCVD — as determined by an ASCVD risk factor tool.
These tools (there are a number of them) use various atherosclerotic risk factors to calculate the likelihood that an individual will have a heart attack or stroke (essentially, the same process as a heart attack, except in the brain) in the next 10 years. It is a probability, not a certainty. Low risk is less than 5%; borderline is 5% to 7.5%; intermediate is 7.5% to 20% and high risk is greater than 20%.
In that perfect world where no one crashes their motorcycle, and all of us have perfect blood pressure, pristine cholesterol levels, tightly controlled diabetes and never smoke, these risk-factor tools would be meaningless and unnecessarily anxiety provoking. You’ve done all you can, so why worry? After all, getting older is a major risk factor, though not reversible, practically speaking.
But we can all use a little motivation. Tight diabetic control, for example, doesn’t come without effort — diet control, weight loss, medications — or even possible side effects, such as an occasional low blood sugar. And most of us feel more motivated when both the risk and the reward are higher.
Searching for the Evidence
So, while ASCVD risk tools try to answer the question, "What is the statistical probability of having a stroke or heart attack from in the next 10 years?" the CAC tries to determine, "Does this patient have actual — not just statistical — evidence of ASCVD?"
Dr. Michael Miedema, a cardiologist at the Minneapolis Heart Institute, who specializes in heart disease prevention, is a fan of CAC scoring.
“It’s, basically, the only test we have that trumps age in terms of its ability to predict cardiovascular mortality,” Miedema says. “And interestingly, it’s quite predictive of all-cause mortality as well, primarily because of what are called ‘shared risk factors’— things like smoking that not only increase cardiovascular mortality but also increase cancer mortality.”
A CAC screening is simple to do. It takes about 10 minutes and uses about 1 to 1.5 millisieverts (mSv) of radiation (the average U.S. citizen is exposed to 3 mSv of background radiation every year, mostly from cosmic rays and radon in the home).
CAC screening isn’t always covered by insurance, and usually runs in the $100 to $400 range. In the metropolitan area where I work, CAC screening is almost never covered, so screening providers offer patients the option of paying the lowest charge out-of-pocket.
A “calcium score” of 1 to 10 indicates minimal evidence of coronary artery disease; 11 to 100 mild evidence; 101 to 400 moderate evidence and over 400 suggests extensive coronary artery disease.
There are two major caveats to interpreting a CAC score:
First of all, of course, a CAC of zero is very good news. “If you are in your seventies with zero CAC, on average, you’ve got more years ahead of you than if you’re in your fiftiess with a high CAC score,” notes Miedema. But “on average” is a statistical measurement, a probability, not a certainty — and people routinely defy statistics.
A CAC of zero doesn’t mean you couldn’t have coronary artery disease; it only means that you don’t have the more advanced kind of atherosclerosis that has been around long enough to have acquired calcium.
Unfortunately, there are times when the inflammatory process that causes atherosclerosis can really kick into high gear, causing a non-calcified, early stage, mildly narrowed atherosclerotic coronary artery to suddenly close off.
So, even with a CAC of zero, you still need to pay attention to controlling your risk factors.
The second caveat: the CAC score is a calculation of the overall atherosclerotic condition in the two arteries that feed the heart, but can’t reliably tell us whether that atherosclerosis is spread evenly throughout the arteries or whether it is concentrated in a few tight areas — the kind of blockages that sometimes require angioplasty or “bypass” surgery.
A patient could have a CAC score of 600, but the disease might be widely scattered and not narrow enough to limit blood flow in any particular area. And a patient with a CAC of 300 might have all of that atherosclerosis focused in one area of one coronary artery. Only a coronary angiogram can visualize directly what the coronary arteries look like on the inside.
So, can a CAC screening help prevent a heart attack? Yes. Preventive medicine can be complicated, but for certain patients, it looks like CAC screening could provide the clarifying information that will motivate them to double down on their heart health.