January 10th, 2014
ESC Spotlights Growing Problem of Radiation Exposure in Cardiology
Larry Husten, PHD
Both medical professionals and patients have a general sense that radiation used in medical imaging and procedures carries some danger, but they often underestimate the risk. And certainly most are unaware of the increasingly large proportion of the problem occurring during cardiology procedures.
“Cardiologists today are the true contemporary radiologists,” said Eugenio Picano, lead author of a report from the European Society of Cardiology published in the European Heart Journal. “Cardiology accounts for 40% of patient radiology exposure and equals more than 50 chest X-rays per person per year,” he said in a press release. And cardiologists themselves can be exposed to radiation at two to three times the levels of diagnostic radiologists, according to the report.
The major barrier to recognizing the problem, of course, is that it may take decades before cancers emerge as a result of the radiation. Further, the authors note, “radiation-induced cancer is clinically undistinguishable from a spontaneously occurring cancer.”
Many patients are exposed to high doses of radiation (>50 mSv) for which there is epidemiological evidence showing a link to cancer. The authors estimate that patients exposed to 100 mSv, which is equivalent to about 5000 chest x-rays, will have “an additional risk as high as 1 in 30 or as low as 1 in 300.”
Nuclear cardiologists can receive as much as 2-5 mSv a year while interventional cardiologists and electrophysiologists have an annual exposure of about 5 mSv, which is two to three times higher than the exposure of diagnostic radiologists. This exposure, they calculate, results in “a typical cumulative lifetime attributable risk on the order of magnitude of 1 cancer (fatal and non-fatal) per 100 exposed subjects.”
Children, of course, are at greatest risk, “because they have more rapidly dividing cells and a greater life expectancy.”
“Even in the best centers, and even when the income of doctors is not related to number of examinations performed, 30 to 50% of examinations are totally or partially inappropriate according to specialty recommendations,” said Picano, in the press release. “When examinations are appropriate, the dose is often not systematically audited and therefore not optimized, with values which are 2 to 10 times higher than the reference, expected dose.”
OK so you have our attention, what is the source of the radiation? I assume that the majority of the radiation comes from nuclear stress imaging. Perhaps the next largest dose comes from the cath lab. Correct me please if my assumptions are wrong.
Can we achieve the same or better results with much less stress imaging and much less angiography? I think we can and must.
The literature shows us clearly that revascularization does not reduce heart attacks or coronary death. It does reduce symptoms. It therefore seems a total waste of resources and radiation to ever do a nuclear stress test on an asymptomatic individual.
The literature also shows that medical management is 90% as effective as revascularization in reducing angina long term. It would follow that even in subjects presenting with angina, we should treat medically and reserve stress imaging, angiography, FFR measurements, and stenting only for those who have persistent limiting symptoms after an effective trial of medical management.
Q: So how do we know if a subject’s symptoms are from coronary disease if we don’t do stress testing?
A: Well there is a simple, very low radiation, very accurate test for the diagnosis of coronary disease, it is called calcium imaging. If you are fortunate enough to have access to an EBT imager, the radiation dose is only 0.7 msv. Helical scanners give more radiation but the technology is improving in this realm.
Q: The calcium score does not show soft plaque or degree of obstruction, how can it replace stress imaging?
A: The calcium score is the strongest measure of heart attack risk available, dramatically better than risk factors or stress imaging. Finding obstruction is not a part of stratifying heart attack risk. Individuals with a score of 0 and obstructive disease are very rare and as it happens, remain at low risk for heart attacks and very low risk for coronary death.
Q: SO you would propose abandoning the high radiation stress tests, angiography and stenting in favor of treatment based on coronary calcium?
A: Yes. That is what I do in my practice with great success, reducing stress testing from 7 subjects a week to 3 subjects a year. I still have about 2 patients a year receive stents (a dramatic reduction from years past). In addition my current annual MI rate is < 0.05%, a dramatic reduction from my prior experience using stress testing as part of my protocol.
Ironically, coronary calcium imaging has historically been criticized for being too much radiation. Current studies demonstrate that an extremely small percentage of the coronary vascular industry radiation comes from calcium imaging. Perhaps if we did more low radiation calcium scores, stratified risk accurately, initiated medical management appropriately, we would not only see a reduction in net medical radiation but also a dramatic reduction in heart attacks and coronary death.
Whatever happened to stress-echo as an alternative to nuclear imaging?
In the appropriate patient with good windows – stress echo is a very viable option and my preferred imaging modality.
Dr. Blanchet makes a good point. However, it is applicable to a degree, and only to an asymptomatic patient for purposes of further risk stratification. I would never be comfortable with an anatomical definition of disease as a substitute for a functional evaluation. There is so much more to the stress test than perfusion imaging:
1. Exercise tolerance is the single, most important predictor of cardiovascular and total mortality.
2. Hemodynamic responses are helpful for diagnosis, prognosis and exercise program prescription.
The perfusion imaging must be used according to the APPROPRIATENESS CRITERIA. When done so, it is a valuable and valued tool. The perfusion imaging is different by modality with PET providing a non-invasive FFR that is more predictive of events than invasive FFR. Thus, it is inappropriate to use ‘one-fits-all” approach. The stress echo is known for high specificity and lower sensitivity, a situation completely opposite of perfusion imaging. However, the outcomes of these tests are predicated by pre-test probability more than by anything else. The principle of ALARA (as low as reasonably achievable) is now extrapolated to patients, with advent of new technology and dose reduction.