Patients admitted to hospital for acute myocardial
infarction receive high ionizing radiation dose during stay
Acute myocardial infarction patients received an average
total dose of ionizing radiation equal to 725 chest X-rays from medical tests
during their hospital stay, according to research presented at the American Heart
Association's Scientific Sessions 2009.
In the first large study to examine total radiation dosage
in heart attack patients, researchers found those admitted to academic hospitals
had a cumulative effective radiation dose of 14.5 millisieverts (mSv) - about
one-third the annual maximum accumulation permitted for workers in nuclear power
plants and other ionizing radiation environments.
"It's potentially a new way to consider radiation exposure
and safety," said Prashant Kaul, M.D., lead author of the study and a fellow in
cardiovascular medicine at Duke University Medical Center in Durham, N.C. "We
think physicians should not only have a greater awareness of dose accumulation
from the tests they are ordering, but also understand the testing patterns they
use for common diagnoses."
Total short-term exposure likely counts, he said. A person's
lifetime exposure to ionizing radiation can potentially increase the risk of cancer.
However, risk estimates vary for developing malignancies at specific exposure
levels.
Physicians perform several billion imaging studies annually
worldwide, about one-third of them in cardiovascular patients. The collective
dose received annually from ionizing radiation medical tests increased an estimated
700 percent between 1980 and 2006, according to the American Heart Association.
Kaul urged increased efforts to better determine the
appropriate use of various radiation-based tests when assessing and treating heart
attack patients.
"We should not withhold necessary, appropriate tests
that involve ionizing radiation - they provide very important information," Kaul
said. "What we should do is evaluate and understand the clinical indications for
tests that involve ionizing radiation. We need to be sure they are being done
appropriately."
Researchers analyzed data from 64,074 patients - 23,394
women and 40,680 men - treated for acute heart attack between 2006 and the second
quarter of 2009 at 49 academic hospitals throughout the United States that participate
in the University Health System Consortium and subscribe to their resource manager
database.
Among the study's findings:
- Patients received 276,651 tests that used ionizing radiation, an average
of seven per patient.
- Patients averaged a total accumulation of 14.52 mSv during their hospital
stay.
- Among the nine types of tests analyzed, 83 percent of all patients received
chest X-rays; 77 percent had catheter procedures; 15 percent underwent body computed
tomography (CT) scans; and 12 percent had a head CT.
- Between 1 percent and 6 percent of patients had three other nuclear imaging
tests and chest CT.
Physicians tend to focus on the radiation dose of each
procedure rather than the cumulative dose a patient will receive, he said. "This
makes the risk seem smaller to patients than it actually is. The risk at an individual
level is small with one test, but with multiple tests the risk likely increases.
Additionally, a small individual risk applied to a growing and aging population
could potentially represent a future public health problem, especially if the
trend continues to be increased use of cardiac imaging tests involving ionizing
radiation."
The study has several limitations. For one, the researchers
used estimates of typical effective radiation doses from several sources, including
the American Heart Association Committee on Cardiac Imaging. Thus, their reported
cumulative and radiation dose per patient is an estimate rather than actual measurement.
Moreover, the researchers selected nine tests used in
assessing heart attacks for their study, but physicians may also use others.
Manesh R. Patel, M.D, is co-author of the study.
Author disclosures are on the abstract.
Duke University Division of Cardiovascular Medicine funded
the study.
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