Heart scans not recommended for asymptomatic patients
How much radiation exposure do people get when their doctor orders up a CT heart scan, a technology capable of producing dazzling 3-D images of the heart?
On average, about as strong a dose as that produced by 600 chest X-rays, according to a report published today in the Journal of the American Medical Association.
That’s reason to avoid the scans if you don’t have pre-existing symptoms of heart disease, such as chest pain, shortness of breath or exercise intolerance, according to Dr. Thomas Gerber, one of the authors and a cardiologist at the Mayo Clinic in Florida. For asymptomatic patients, the known risks outweigh the potential benefits.
“There is currently no data, no research that supports the use of coronary CT angiography in patients who have no symptoms of heart disease,” Gerber said.
Radiation exposure is associated with a small but enhanced chance of developing cancer. While acknowledging that estimates of exposure are imprecise, the JAMA study found that radiation doses vary widely between medical centers performing heart scans - from a low of 4.6 millisieverts to a high of 30 millisieverts.
The median exposure was 12 millisieverts, the equivalent of 600 chest X-rays. That’s more that twice as high as the 5 millisieverts typically associated with invasive coronary angiography, an alternative procedure, but about equal to the exposure associated with a nuclear stress test.
Gerber emphasized that the risk is acceptable if someone has signs of potential heart disease, the No. 1 killer in America. Half of people struck for the first time by heart attacks die, he noted. In someone with symptoms, scans can help physicians detect obstructions in coronary arteries and modify treatment regimens.
There is no evidence, however, that detecting plaque in people without symptoms makes a difference in outcomes, Gerber said. Even if physicians modify therapy for patients, such changes have not been shown to prolong people’s lives or significantly reduce the burden of disease.
The findings are important because CT heart scans are being offered widely to patients by hospitals and cardiologists. In the last two years, the number of scanners in cardiology practices has tripled, according to an editorial accompanying the JAMA article.
Anecdotal reports indicate that some physicians are recommending scans for asymptomatic patients in the hope of catching heart disease at a very early stage – despite a lack of evidence supporting the practice.
Also, while the risk of radiation from a single scan may be extremely small, medical scans of all kinds are being used with much greater frequency.
According to an American Heart Association science advisory published Monday in the journal Circulation, radiation doses to the U.S. population from medical tests and procedures increased more than 700 percent between 1980 and 2006.
See this article from last year’s New York Times for more details.