In addition to possible death and myocardial damage, acute heart attack patients routinely accept the additional risk of cardiovascular imaging exposing them to ionizing radiation, according to research presented Nov. 16 at the 2009 American Heart Association meeting in Orlando, FL.
Possibly the first large study to examine total radiation dosage in heart attack patients has determined that patients treated for myocardial infarction in academic hospitals underwent diagnostic imaging and fluoroscopy-guided interventions that exposed them to an average cumulative effective radiation dose of 14.5 mSv, about one-third the annual maximum accumulation permitted for workers in nuclear power plants and other ionizing radiation environments.
"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." said principal investigator Dr. Prashant Kaul, a cardiovascular medicine fellow at Duke University Medical Center in Durham, NC.
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."
Kaul and colleagues analyzed data from 64,074 patients (36% women), who were treated for acute heart attack between 2006 and the second quarter of 2009 at 49 academic hospitals in the U.S. All the facilities 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% of all patients received chest x-rays, 77% had catheter procedures, 15% underwent body computed tomography (CT) scans, and 12% had a head CT.
- Between 1% and 6% 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, according to Kaul.
"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," he said. "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 AHA Committee on Cardiac Imaging. Thus, their reported cumulative and radiation dose per patient is an estimate rather than an actual measurement. Moreover, the researchers selected nine tests used in assessing heart attacks for their study, but physicians may also use others.
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% between 1980 and 2006, according to the AHA.