Major bleeding complications are common after acute coronary syndromes (ACS) and are associated with increased mortality. Thus, identification of high bleeding risk (HBR) patients during clinical decision making can be lifesaving. The Academic Research Consortium for High Bleeding Risk (ARC-HBR) criteria are recommended for bleeding risk assessment in ACS. This thesis investigated the prevalence of HBR and its association with major bleeding complications and major adverse cardiovascular or cerebrovascular events (MACCE) in ACS patients, with a focus on ST-elevation myocardial infarction (STEMI). Furthermore, bleeding and ischemic risk factors not included in the ARC-HBR criteria were identified. The study population was identified by a database search and data was collected by patient record review.

Study I included 212 suspected non-ST-segment elevation myocardial infarction patients and 209 of these were in study II. Study III included 1564 STEMI patients and the 1367 treated with primary percutaneous coronary intervention (PPCI) were in study IV. The prevalence of HBR among ACS was over 40%. Among STEMI, the 1-year major bleeding incidence in HBR patients was over 10% (3-fold increased risk vs. non-HBR). However, only few individual criteria were independent bleeding predictors. Current smoking was identified as a major bleeding risk factor, and the prevalence was 40.4% among patients classified as non-HBR according to the ARC-HBR. This finding suggests that guideline recommended bleeding risk assessment failed to identify a large proportion of patients who were at HBR, demonstrating the need to consider risk factors not included in the ARC-HBR framework. The 1-year incidence of MACCE after PPCI for STEMI among HBR patients was 19.5%, corresponding to a 3.3-fold risk compared to non-HBR. After accounting for comorbidities such as diabetes and reduced left ventricular ejection fraction, it seems that the higher incidence of MACCE among HBR patients could be explained by underlying conditions and not only bleeding risk status itself. Careful evaluation of ischemic risk factors is warranted, particularly among HBR patients to adequately assess the balance of these opposing risks.