2.4. Data linking

Patients in the VHR registry were linked to the 2 administrative databases using unique patient identifiers, and records that could not be linked (out of province residence or invalid patient identifiers recorded in VHR) were removed. For patients with >1 STEMI hospitalization in VHR, only the first instance was retained in the cohort. To define the index STEMI hospitalizations in the administrative data, the patients in VHR were linked to corresponding hospitalizations in the inpatient DAD, as under the VHR protocol most patients are admitted directly and skip the Emergency Department, and so do not have an index record in NACRS. Because VHR includes patients transferred from other hospitals, we accounted for transfers in the administrative data by combining concurrent hospitalization records, into an episode of care. Therefore, the index hospitalization defined by the administrative DAD data sometimes contained >1 DAD record (but with dates overlapping with those recorded in VHR).