The data

The data are from the Health Person-Oriented Information Database, a linkable version of provincial computerized hospital discharge records from the Canadian Institute for Health Information Discharge Abstract Database. These hospital records have been linked to form patient trajectories.

The provinces included in the analysis were Nova Scotia, New Brunswick, Quebec, Ontario, Manitoba, Saskatchewan and Alberta. Newfoundland and British Columbia were excluded because of anomalous provincial coding practices, and Prince Edward Island was excluded because the province had no revascularization facilities. To ensure a reasonable number of heart attack patients, this study examines only health regions with a population of 100,000 or more—a total of 46.

The analysis focuses on two fiscal years: 1995/1996 (the first year of the Person-Oriented Information Database) and 2003/2004. The year 2003/2004 was the last one for which all provinces involved could be followed up. Patients aged 20 or older were included if they had been admitted to hospital with the most responsible diagnosis being acute myocardial infarction (ICD-9-CM code 410; ICD-10-CA codes I21 or I22),^11, 12 provided that they had not been hospitalized with acute myocardial infarction in the preceding 365 days. The purpose of the one-year “wash-out” period was to start the analysis with a new episode of acute myocardial infarction. For each patient, two events were examined: whether they received revascularization treatment and whether they died in hospital within 30 days of admission. The latter has been shown to be a good estimate of the total mortality rate.¹³  

Revascularization procedures were defined with the algorithm described by the Canadian Institute for Health Information as follows: percutaneous coronary intervention (ICD-9-CM 36.01, 36.02, 36.05 or ICD-10-Canadian Classification of Interventions 1.IJ.26, 1.IJ.50, 1.IJ.57) and coronary artery bypass graft surgery  (ICD-9-CM 36.1 or ICD-10-CCI 1.IJ.76).^11, 12, 14 These procedures are used to treat coronary artery disease, a condition in which fatty deposits accumulate in the cells lining the artery wall and obstruct blood flow. For percutaneous coronary intervention, a large peripheral artery (usually the femoral artery in the leg) is punctured with a needle and a guide wire is threaded through the needle into the arterial system, through the aorta and into the obstructed coronary artery. A catheter with a balloon attached to the tip is threaded over the guide wire and into the obstructed area. The balloon is inflated for several seconds. To keep the artery open, a wire mesh device (stent) may be inserted. Coronary artery bypass graft surgery involves grafting veins (usually from the leg) or arteries (usually from beneath the breastbone) from the aorta to the coronary artery, thus bypassing the obstructed area.

Direct standardization was used for age-sex adjustment. The standard population was acute myocardial infarction patients in the seven provinces in fiscal year 1995/1996, by five-year age group. Only age and sex were used for standardization; previous work has shown that including a co-morbidity index did not substantially change the results.⁸ 

The Postal Code Conversion file was used to identify Census Dissemination Areas from the patient’s residential postal code. Health region (as of 2005) was based on the Census Dissemination Area.

A limitation of the data is that patients cannot be followed across provinces.