Exposure to low-dose ionizing radiation from cardiac imaging among patients with myocardial infarction.

Patients with first acute myocardial infarction (AMI) constitute a demographic that is exposed to significant amounts of low-dose ionizing radiation (LDIR) over a short period. The aim of this study was to describe cardiac LDIR exposure trends among patients with first AMI over a recent approximately 10-year period. Administrative databases were used to identify a cohort of 106,803 patients who had first AMIs in Quebec, Canada, from 1996 to 2004. These patients were followed through 2007, and the use over time of cardiac imaging procedures associated with LDIR was documented using a cumulative exposure variable. Exposure was documented in 2 periods: the acute phase (<1 month after AMI) and the chronic phase (1 month to 3 years after AMI). The mean dose of cardiac LDIR incurred in the acute post-AMI phase increased twofold during the study period, from 6.8 to 11.8 mSv/patient. However, the mean dose of cardiac LDIR incurred in the chronic post-AMI phase decreased, from 8.3 to 7.3 mSv/patient. Overall, there was a 26.4% increase in cumulative cardiac LDIR exposure, to a mean of 19.1 mSv/patient in the 2 years after AMI, which was driven primarily by an increase in percutaneous coronary interventions. When patients were stratified by cumulative LDIR exposure, several predictors of heavier LDIR exposure were identified among the strata of exposed patients, including younger age and the absence of acute and co-morbid conditions, and the heaviest exposed group subsequently had the lowest overall mortality. In conclusion, among patients experiencing first AMI in Canada, exposure to cardiac LDIR increased over a recent approximately 10-year period. However, the observed trend is toward increasing use of therapeutic procedures with proven mortality benefit undertaken earlier in the disease course and away from diagnostic procedures in the subsequent years after AMI.