Abstract 19280: Exposure to Low-Dose Ionizing Radiation from Cardiac Imaging among Patients with Myocardial Infarction in Canada: 10-Year Data from a Large Canadian Longitudinal Cohort
Background: The use of cardiac imaging procedures involving low-dose ionizing radiation (LDIR) is becoming increasingly recognized as a source of significant radiation exposure. Data has emerged to document increasing use of such imaging in the United States (U.S.), however, comparative trends from countries with alternative healthcare systems is largely lacking.
Methods: We created a retrospective longitudinal cohort of 106,803 patients who suffered a myocardial infarction (MI) in Quebec, Canada, between 1996 and 2004, and documented exposure to 3 commonly-used cardiac imaging procedures involving high amounts of LDIR: myocardial perfusion imaging (MPI) with technetium (99mTc) sestamibi and 201thallium isotopes [15.6 mSv], diagnostic cardiac catheterization [7 mSv], and percutaneous coronary intervention (PCI) [15 mSv]. The exposure variable was mean cumulative dosage of LDIR from cardiac imaging, documented in 2 periods: the early post-MI (< 1 month after MI) and stable coronary artery disease (CAD; 1 month to 3 years after MI) periods. Rates were defined as percent of patients receiving one or more test during the specified period (either 1 month or 35 months).
Results: Cumulative exposure to cardiac LDIR increased progressively over the ten years in the early phase post-MI (5.2 to 12.8 mean mSv), whereas a small decrease in LDIR exposure was seen in the stable period. Overall, the heavier-exposed categorical group contained younger patients than the lesser-exposed group. Rates of diagnostic cardiac catheterization and PCI usage in the early phase post-MI increased (30.5% to 65.4% for cardiac catheterization, 12.5% to 47.6% for PCI). Rates of catheterization in the stable CAD phase showed a decreasing trend: 19.8% to 14.0%. Rates of MPI were similarly deceased in both the early (6.9% to 3.9%) and stable (9.5% to 5.4%) periods.
Conclusions: As in the U.S., exposure to LDIR from cardiac imaging among patients with CAD in Canada is rapidly increasing. However, this trend is driven solely by increases in the early use of catheter-based procedures following MI. In contrast to the U.S., rates of MPI usage in Quebec, Canada, are declining. Whether or not this difference in practice patterns affects outcomes raises an important hypothetical question.
- © 2010 by American Heart Association, Inc.