LAUSR

Objective To assess the short-term risk of acute myocardial infarction (AMI) associated with procedures performed at outpatient specialised hospital clinics. Methods In this case-crossover, population-based study, we identified first-time AMI cases aged ≥40 years via patient registries and linked them to their surgical intervention in Norway (2008–2016) and Sweden (2001–2014), respectively. The number of individuals with AMI who underwent procedures 0–7 days (hazard period) prior to the AMI diagnosis was compared with cases who were exposed 29–36 days (control period) before the AMI. A total of 6176 patients with AMI who underwent a procedure either during the defined hazard or control period contributed to the analyses. ORs with 95% CIs were computed using conditional logistic regression. Results The mean age of the total population was 74.7 years and 64.6% were male. The relative risk was higher following procedures performed under general/regional anaesthesia for gastrointestinal endoscopy (ORsummary, 4.23, 95% CI 1.58 to 11.31), vascular (ORsummary, 3.12, 95% CI 1.10 to 8.90), urological/gynaecological (ORsummary, 2.30, 95% CI 1.50 to 3.53) and orthopaedic (ORsummary,1.78, 95% CI 1.30 to 2.44) procedures, and for ENT (ear, nose and throat) and mouth procedures (ORsummary, 1.53, 95% CI 1.19 to 1.99) performed under local anaesthesia. Conclusion This large population-based register study from two countries suggests that outpatient procedures are generally safe with regard to the postoperative risk of AMI. However, some procedures, such as gastrointestinal endoscopy, vascular procedures and urological/gynaecological procedures may increase the risk of AMI by twofold or threefold within the first 8 days after the procedures. Further studies are warranted to assess whether the effect is modified by cardiovascular medication or other clinical factors.