Acute Myocardial Infarction in Iceland, is There a Gender Difference in Treatment and Survival?
Condition: Acute Myocardial Infarction; Coronary Angiography
MeSH terms: Myocardial Infarction; Infarction
Study type: Observational

Summary: 
      All patients in Iceland with STEMI (2008-2018) and NSTEMI (2013-2018) that underwent coronary
      angiography and had obstructive coronary artery disease were included. Information about
      patients and angiography results and treatment were obtained from the Swedish Coronary
      Angiography and Angioplasty Registry (SCAAR). Survival was estimated with Kaplan-Meier
      method. Cox regression analysis were used to identify significant risk factors for long-term
      mortality. Relative survival was defined as observed survival divided by expected survival of
      the population of Iceland
    

Detailed description: 
      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.
    

Observational model: Other
Time perspective: Retrospective
Sampling method: Non-Probability Sample
Study population: 
        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).
      
Keywords: Acute myocardial infarction; Gender difference; Long-term survival; Excess mortality