Acute Myocardial Infarction in Iceland, is There a Gender Difference in Treatment and Survival?

Methods This is a retrospective observational nationwide study of all patients, aged 18 years and older, who underwent coronary angiography for acute myocardial infarction (AMI) during the study period. All procedures were performed at Landspitali University Hospital, which is a tertiary referral center and the only institution performing coronary angiographies in Iceland. The study period was from January 1, 2008 to December 31, 2018 for ST elevation myocardial infarction (STEMI and from January 1, 2013 to December 31, 2018 for non-ST elevation myocardial infarction (NSTEMI). For multiple admissions, the first was retained.

Information about patient demographics, cardiovascular risk factors, comorbidities, angiography results and treatment were obtained from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR), a Swedish Web-based database also used in Iceland that prospectively record both patient- and procedure-related factors. All data are registered by the treating physician and nurses at the time of the procedure.

Clinical definitions Cases of acute myocardial were defined as STEMI and NSTEMI, according to the current European Society of Cardiology guidelines, and determined by the attending cardiologist [18]. The NSTEMI diagnosis was introduced into the database 2013 and there was also a change in the Troponin analysis used at that time. This is the reason why we chose to have a shorter study period for the NSTEMI patients. We excluded patients that had not significant coronary artery stenoses. Cardiovascular risk factors, including hypertension, diabetes mellitus, smoking status, statin use, body mass index (BMI) and renal function were recorded. Chronic kidney disease (CKD) was staged according to the Kidney Disease Outcome Quality Initiative (KDOQI) classification. Estimated glomerular filtration rate (eGFR) was calculated from serum creatinine measurements using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, and CKD was defined as eGFR < 60 mL/min/1.73 m2 (stage 3-5).

Prior MI, percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG) were recorded as defined in the database. Since these were AMI patients, they were all done urgently but it was also recorded whether they were done acutely as primary PCIs. The results of the coronary angiography were expressed as the number of vessels involved with significant stenoses or left main stem disease based on angiographic results. If PCI was performed, it was recorded whether patients received aspirin (acetylsalicylic acid) or adenosine diphosphate receptor (ADP) inhibitor before or during the procedure. The choice of treatment, medical therapy alone, PCI or CABG, was at the discretion of the attending interventional cardiologist and/or the heart team.

Observed and Expected Survival Data for all-cause mortality were extracted through linkage with Statistics Iceland. Patients were followed up for their vital status after hospitalization, with censoring at the end of follow-up on October 23, 2019. Expected survival was derived from the general population of Iceland matched to observed survival for the study population by sex, age and year of hospitalization.

Statistical analysis All calculations were performed using R software version 3.3.3 (R Foundation for Statistical Computing, Vienna, Austria). All continuous variables were normally distributed and were compared with Student´s t-test and presented as mean ± standard deviation (SD). Categorical variables were compared using Chi-square test if the observed data was over five, otherwise Fisher´s Exact test was performed. Statistical significance was prespecified at 5% (P < 0.05) Kaplan-Meier curve was plotted to assess the estimated long-term survival and the two groups were compared using a log-rank test. To identify independent prognostic factors for survival, a Cox multivariate analysis was used, represented as hazard ratios with 95% confidence intervals.

Relative survival was defined as the observed survival among patients with AMI divided by expected survival in populace of Iceland matched by sex, age and year.

As individual patients were not identified, obtaining individual consent for the study was not obtained.