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Can a Test be used to Reduce Over-testing? Maybe!
November 7, 2015
Coronary Artery Calcification can be scored by a CT scan (CAC score) and may help determine who may or may not be at risk of having a hard cardiac event (heart attack or sudden cardiac death) in the next year. In fact, as the BRCT shows, of people who have a negative CAC score, only one out of 1000 of them will have a cardiac event in a year, meaning that 999 of them do not have to worry. That is pretty reassuring!
Many patients, and their doctors, are interested in determining if they are at risk for heart attack or sudden cardiac death. We know from ample studies that random EKG’s and stress tests are not helpful in this regard, something that we discuss at length in a chapter of our book. 70-80% of heart attacks occur in blood vessels that are not blocked, and the only purpose of a stress test is to discover arteries that have some blockage in them. Therefore, a normal stress test in no way can reassure a patient that he/she is not at risk for a heart attack; 80% of heart attacks occur in people with a normal stress test. Also, an abnormal stress test does not help people either. If a stress test discovers a blockage and that blockage is fixed (either by stent or bypass surgery), under most circumstances there will be no decrease in the chance of getting a heart attack or cardiac death since most heart attacks do not occur in blocked arteries. And most abnormal stress tests occur in people without blockages; false positives are common, and patients often have to undergo dangerous tests to prove they do not have heart disease.
Is there a better way to ascertain who is at risk? Recently, especially after the publication of two new studies, some attention has been placed on Coronary Calcium Scoring (CAC), a means of determining how much calcium is built up in the heart arteries by means of a very quick and inexpensive ($70) CT scan. Calcium is a marker for blood vessel plaque, and it is the rupture of plaque (primarily in arteries that are not blocked and would thus not show up in an EKG or stress test) that causes heart attacks and sudden death. In people who may be a higher risk of heart disease, such as those with risk factors like diabetes or other vascular disease or a strong family history, CAC scoring may help determine who should be worried about a pending heart attack, and who could be reassured. But how good is CAC scoring at determining real clinical outcome? We reviewed much of the available literature on CAC scoring, and discussed this with a preventive cardiologist who is a prolific researcher in the subject, and are cautiously optimistic.
It turns out that a completely normal CAC test (score of 0) is very helpful. Of people who score 0 and are at some risk of heart disease by Framingham criteria, only 1/1000 progress to a heart event in a year. That means that 99.9% of people will not get a cardiac event. Two recent studies showed that about half of people told that they are at risk for heart disease by Framingham criteria turn out to have a CAC score of 0 and thus can be reassured that they are actually not at risk. Many of them had been told to take statins and aspirin, to get stress tests, to see cardiologists, while in fact the CAC score of 0 would imply that they do not need any of these interventions. Similarly, a low CAC score of 1-10 is similarly reassuring; 5/1000 progress to heart events in a year. Once you get to higher CAC scores the risk of heart disease increases, although it remains low until the CAC is very high. A score over 100 puts 20/1000 at risk in a year, a score over 1000 puts 180/1000 at risk in a year.
Many of these people at high risk do not have any blockages on a stress test, while some people with lower scores may have blockages. The presence of blockages is not as relevant to who is going to get a heart attack as is the presence of plaque. Therefore, simply having a high CAC score does not imply that a person should get a stress test and, if a blockage is found, have it stented or bypassed. That misses the point entirely. One caveat is that people who do have cardiac symptoms such as chest pain, or people with very high CAC scores over 1000, may be at risk for very serious blockages that should be opened (diseases of proximal LAD or Left Main ateries), and thus a doctor has to use judgment as to whether or not a stress test or catheter is indicated based on the individual patient’s presentation. However, modestly high CAC alone should not be the only reason to do more testing or to assume there is a blockage that needs to be opened.
If people are determined to be at risk for cardiac disease, how can that risk be decreased? Certainly diet and exercise are paramount. Reduction of risk factors (poorly controlled blood pressure or diabetes, smoking, obesity) is also crucial. Aspirin may help reduce the risk a bit, and statin cholesterol medicines can reduce risk by as much as a third. Statins work not by lowering cholesterol, but rather by removing and/or stabilizing plaque in the arteries and making them less prone to rupture (which is why measuring cholesterol is not important in the decision of whether to use statins, while a CAC score is much more useful). Thus, if someone has a CAC score of 120, and their risk of heart disease in the next year is approximately 20/1000, the use of statins and asprin may reduce that risk to 10-12/1000. The absolute reduction of risk in this case is 10/1000, or 1% less chance of having a heart attack. It is really up to each individual as to whether that benefit is worth taking those medicines. But more importantly, if someone is told that they should be on statins and aspirin, and they have a CAC score of 0, there is virtually no improvement with the medicines, and thus no justification for taking them. In this way, if it is conducted sensibly and on the correct group of patients who may be at risk of heart disease, normal CAC can lead to a reduction in over-testing and over-treatment. It is not every day that a test can accomplish those results!