Higher rates of coronary angiography and revascularization following myocardial infarction may be associated with greater survival in the United States than in Canada

BACKGROUND: Significant differences are known to exist, between the United States and Canada with respect to coronary catheterization and intervention . In a post hoc analysis, it was hypothesized that these differences may ha ve the greatest impact on outcome in patients at risk for recurrent events such as those following myocardial infarction (MI). PATIENTS AND METHODS: The hypothesis was tested in a nonrandomized comparis on of the catheterization and revascularization patterns for patients follo wing acute MI in 7029 patients in the United States and 1774 patients in Ca nada who participated in the Coumadin/Aspirin Reinfarction Study (CARS). CA RS tested the effectiveness of low dose warfarin in combination with acetyl salicylic acid (ASA) Versus ASA alone in reducing cardiovascular morbidity and mortality. RESULTS: Before study enrolment (median day 7 to 8), 84.5% of the American patients underwent coronary angiography compared with only 7.7% in Canada ( P<0.01). CARS patients in the United States underwent significantly more fr equent angioplasty during their hospital admission before study enrolment t han their Canadian counterparts (55.8% versus 3.0%, respectively, P<0.01), and there was a more frequent use of intravenous heparin among American CAR S patients (96% versus 88%, respectively, P<0.01) but less frequent adminis tration of thrombolytic therapy (44% Versus 49%, respectively, P<0.01). For follow-up of up to 32 months, American CARS patients had significantly few er primary events (cardiovascular deaths, nonfatal MI, nonfatal ischemic st roke) than Canadian patients. Cumulative estimate of a primary end point co mparing American with Canadian patients was, respectively, 2.0% versus 3.1% at one month, 8.0% versus 11.3% at one year and 11.6% versus 15.0% at two years. Thus, time to the primary event was significantly longer in American patients (P=0.0001). All-cause mortality estimates at 12 months were 2.2% and 4.0%, respectively, for the American and Canadian CARS subgroups. When management for the index MZ (ie, angiography and angioplasty) is included i n the model, the risk of death for Canadian versus American subgroups of CA RS is not statistically different (0.9, 95% CI 0.6 to 1.2, P=0.40). CONCLUSION: Among study participants, American patients experienced a bette r outcome than Canadian patients, which may be attributable to more aggress ive management based on early coronary angiography and angioplasty. However , angioplasty before study enrolment in American patients may have resulted in enrolment of lower risk patients. This selection bias limits the scope of the comparison.