Last reviewed by Faculty of Harvard Medical School on November 3, 2012
By Thomas H. Lee, M.D.
Brigham and Women's Hospital
A new generation of computed tomography (CT) scanners is making it possible to take very clear pictures of coronary arteries, including any blockages, without the need for more invasive, more expensive procedures. This is a good development, right? Well, yes and no. The latest technologies are fabulous. They are better than the CT scans that are currently in use. As this new generation of scanners takes over, the information they provide will be good enough to guide treatment for most patients — and prevent many of them from needing cardiac catheterization.
But the more important question is not whether the new CT scans are good enough to diagnose coronary artery disease, but are we ready for them? In other words, will we have the judgment to know when to use these new testing technologies, and when to use common sense instead?
Currently, coronary angiography is the "gold standard" test to determine the presence or absence of coronary artery disease, and how severe the problem is. The test is done by cardiologists, costs a few thousand dollars, and carries a low but real risk of complications such as stroke, heart attack, kidney problems, and even death. Because of these costs and risks, physicians usually start with less invasive tests, such as treadmill stress tests, to evaluate patients with possible coronary artery disease.
CT and MRI scans of the heart have been tantalizing us for years with the potential to take remarkably clear pictures of the inside of the body. However, getting a good look at the coronary arteries (the blood vessels that run across the surface of the heart and feed oxygen and nutrients to the heart muscle cells) presents a special challenge. Since our hearts are constantly contracting and expanding, the movement blurs the images of the arteries on most scans — like photos of a speeding car.
Two factors now make it possible to get images sharp enough to actually see the blockages inside the coronary arteries. First, beta-blockers, such as atenolol and metoprolol, are given to slow down the heart rate. Some patients have medical issues that make these drugs risky to use, but most patients with heart disease should be on them anyway. With beta-blockers, the "speeding car" of a heart can be slowed down so we can take a better look.
The new "high tech" factor is the equivalent of using much faster film to photograph that speeding car. Extremely fast CT scans use multiple scanners spinning around the patient to take literally dozens of snapshots of the body from multiple angles. These simultaneous snapshots are used to reconstruct a complete image of what is going on inside the arteries of the heart. And because the snapshots are simultaneous, the images are not blurred.
Conventional CT machines now in use at most hospitals to look for blood clots and other cardiovascular problems generally have four "scanners." The new ones that are creating the sudden excitement about scanning the heart have as many as 64 scanners. The greater the number of scanners, the better the image that can be obtained.
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What's the Concern?
What's not to like about this new technology? It will show whether or not patients have coronary artery blockages without putting them through a coronary angiogram. After all, this approach will be cheaper and safer. One concern is that all CT scanners are not created equal. Doctors may start to order the test and not realize that the testing facility will not immediately be using the latest generation of scanner. This is likely to be a short-term issue, as this new generation of scanners gets out there. Over time, you can expect that many patients will benefit by having more convenient and safer care.
That brings us to what critics of the new scanners are concerned about: Will the new testing approaches be too convenient? Will they be so convenient that doctors will stop trying to figure out what is going on with a patient through careful histories and physical examinations? Will they simply refer them for scans? And will physicians and hospitals have a financial incentive to refer patients to scanners that they own?
In addition to the concern about costs, there are patient-safety issues. There is considerable radiation exposure associated with a CT scan, and if we all undergo them, there will be some small jump in deaths from cancer that results. In addition, these scans will find partial blockages that some patients will want to "fix" with angioplasty and bypass surgery rather than treat with lifestyle changes and medications. What seemed to be a less costly and safer approach can turn into one that leads to greater expense and procedural complications.
These complications will be tragic, because the fact is that people who do not have symptoms of heart disease have a very good outlook — as long as they do their best to control their cholesterol levels and other risk factors for heart disease. However, Americans tend to have trouble living with uncertainty, and many will undergo cardiac procedures to try to make their arteries "perfect."
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The Bottom Line
The newest CT heart scans are clearly an exciting advance. However, we have to first learn how the test will improve our health. Similar to any diagnostic test, doctors and patients should know what questions they want answered from a heart CT scan. Just to find out if you may have some mild blockages at any given time is not a diagnostic question. It is an unproven screening test.
Ideally, we need well-designed medical studies to determine the best use of this new technology. But the scanners will be available soon, well before we have the data. Doctors, consumers and health policy makers will quickly need to figure out how to make the best use of the new technology.
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Thomas H. Lee, M.D., is the chief executive officer for Partners Community HealthCare Inc. He is a professor of medicine at Harvard Medical School. He is an internist and cardiologist at Brigham and Women's Hospital. Dr. Lee is the chairman of the Cardiovascular Measurement Assessment Panel of the National Committee for Quality Assurance.