Heart-imaging tests, such as cardiac computed tomography (CT) and nuclear stress tests, can save lives. Their highly detailed images of the heart and arteries can help determine heart attack risk or diagnose coronary heart disease. But experts have expressed concerns about the potential cancer risks from the ionizing radiation required to perform them.
Other cardiac screenings, including electrocardiogram (ECG, EKG) and echocardiogram, which don’t use ionizing radiation, have also come under fire lately, but for different reasons. Experts say that too many people who don’t need the tests are undergoing them as part of routine risk assessments.
While those procedures don’t cause physical harm, their overuse can still have a negative impact on patients. That's because those tests, and others like them, have a low but definite percentage of false-positive results—suggesting a problem when there really isn’t one—which can cause patient anxiety and lead to further unnecessary testing.
Doctors must consider radiation risks when ordering cardiac imaging for patients, advises the American Heart Association (AHA) in a scientific statement published in 2014 in the journal Circulation.
The AHA also recommends that doctors clearly explain to patients the reasons they’re suggesting cardiac imaging using CT, radiopharmaceuticals (drugs that contain
radioactive materials), and fluoroscopy (X-ray imaging in real time) as well as the benefits and risks involved. You should also understand any risks that may result if you choose not to undergo imaging.
Although the risks associated with low-dose radiation shouldn’t be overstated, it’s still important to understand that higher cumulative radiation exposure is linked to an increased risk of cancer and cell damage, which can take many years to appear.
Tests employing fluoroscopy can cause radiation-induced skin injury shortly after the procedure. The fluoroscopic beam can burn the area of the skin where it’s aimed. “Large doses of radiation can have significant consequences. While evidence linking cancer to small amounts of radiation, such as doses in CT scans and nuclear medicine exams that use small amounts of radioactive material, is limited, most experts agree that it’s wise to avoid unnecessary exposure,” says James L. Weiss, M.D., professor of cardiology and director of the Heart Station at Johns Hopkins University School of Medicine in Baltimore.
“The radiation risk from a single test or even a few tests is small, and the benefits outweigh risks when testing is warranted,” he says. “But if the test isn’t clinically necessary, no amount of radiation is acceptable.”
Routine risk assessment
Another cause for concern is overuse of certain tests for coronary artery disease on healthy patients who don’t have symptoms. In guidelines appearing in the March 2015 issue of Annals of Internal Medicine, the American College of Physicians (ACP) recommends against routine cardiac screenings for low-risk adults (patients who have a less-than-10-percent risk of having a heart attack or other cardiac event).
The ACP found no evidence that routine screening benefits low-risk patients or improves outcomes. Instead, needless ECGs, echocardiograms, and nuclear stress tests can cause undue anxiety in patients. False-positive results can lead to invasive tests and procedures that can be expensive and potentially harmful.
Exercise ECGs carry a very rare risk (less than one in 10,000) of a heart attack or sudden death. ECGs that use drugs to induce the effects of exercise instead of a treadmill carry a low risk of a heart attack, an erratic heartbeat, or a drop in blood pressure. Nuclear stress tests involve injecting a radioactive substance into the body.
Some doctors prescribe routine screening when it’s not clinically required for several reasons, including pressure from patients, avoidance of malpractice suits for not performing a test, and financial incentives.
Other doctors may overestimate a screening’s value and underestimate its harms.
Before ordering a heart test, your doctor will consider several factors, including the test’s diagnostic accuracy, image quality, availability, comfort and cost. Your doctor should counsel you on the benefits and risks of the test he or she recommends. Be prepared to ask questions about the test so you can make an informed decision about your options.
“You should feel entirely comfortable asking for more information about any tests your doctor recommends,” Weiss says.
Here are some questions to ask:
1. Will this test help diagnose or treat my heart problem? The answer should be “yes.” Cardiac tests can determine the cause of symptoms like chest pain, dizziness, or shortness of breath.
2. What are the consequences of not getting the test? Ask if skipping the test might result in a missed or delayed diagnosis and if it could affect your ultimate outcome.
3. Are there other tests that can be used to obtain the information without using ionizing radiation? If a comparable test that doesn’t use radiation, such as echocardiogram or cardiac magnetic resonance imaging (MRI), can provide the same clinical information, it may be preferred.
4. Have you reviewed my radiation exposure history? Your doctor should check your medical records for past exposure, especially if you’ve had frequent imaging tests or changed healthcare providers.
5. Can a previous imaging test I’ve undergone reveal what you’re looking for? Keep track of your tests and let your doctor know about them to avoid repeat testing.
6. How much radiation will I be exposed to? A CT scan can deliver anywhere from 2 to 10 millisieverts (mSv) of radiation, which is considered low risk. In comparison, people get about 3 mSv of radiation each year just from naturally occurring environmental radiation.
7. Will the radiation dose be adjusted for my body? The facility where you have your imaging done should adjust the radiation dose for your weight, heart size, and age. If it uses the same doses for all patients, find another facility.
8. How might radiation exposure affect my risk of developing cancer? Studies haven’t been able to measure the risk definitively. However, older adults are less susceptible to cancer risks because it can take many years for cancer to develop, and the body tissues of people ages 60 and older are less sensitive to radiation’s effects.
If you’re still uncertain about the benefits and risks of a test, the AHA recommends that you and your doctor consult with an imaging specialist. “While no one should have a procedure he or she doesn’t need,” Weiss says, “a CT scan can be a lifesaving test if it provides your doctor with meaningful information to diagnose or treat heart or vascular problems. A good example of this is the critically important use of CT and MRI to detect and quantify aortic aneurysms.”
If you haven’t been doing so, start keeping track of any radiology exams you’ve undergone. You can get a free patient medical imaging card to use to record the date, type, and location of your exams.