A comparison of U.S. and Canadian cardiac catheterization practices in detecting severe coronary artery disease after myocardial infarction: efficiency, yield and long-term implications

OBJECTIVES We sought to compare U.S. and Canada’s post-myocardial infarction (MI) cardiac catheterization practices in the detection of severe coronary artery disease (CAD). BACKGROUND Little is known about the efficiency with which the aggressive post-MI catheterization strategy observed in the U.S. detects severe CAD compared with the more conservative strategy observed in Canada. METHODS From the U.S. and Canadian patients who had participated in the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Arteries trial (n = 22,280, 11.5% Canadian), we examined the frequency of in-hospital cardiac catheterization, the prevalence of severe CAD observed at catheterization (diagnostic efficiency) and the total number of MI patients with severe CAD identified (diagnostic yield). RESULTS The rate of catheterization in the U.S. was more than 2.5 times that in Canada (71% vs. 27%, respectively, p < 0.001). With identical prevalences of severe CAD at catheterization (17%) in the two countries, the higher frequency of catheterization in the U.S. resulted in the identification of more than two and a half times as many cases of severe CAD compared with Canada (12 severe CAD cases identified per 100 post-MI patients in the U.S., vs. 4.6 per 100 in Canada). If considered in isolation, we estimated that these differences in severe disease detection might effect a small long-term survival advantage in favor of the U.S. strategy (estimated 5.0 lives saved per 1,000 MI patients). CONCLUSIONS Canada’s more restrictive post-MI cardiac catheterization strategy is no more efficient in identifying severe CAD than the aggressive U.S. strategy, and may fail to identify a substantial number of post-MI patients with high risk coronary anatomy. The long-term impact of these differences in practice patterns requires further evaluation.