Predictors of arrhythmias, cardiac arrest, and mortality in acute coronary syndrome

Abstract: Background. Patients with acute coronary syndrome (ACS) face a high risk of lethal complications, both during the hospital course and after discharge. The aim of this thesis was to assess patient characteristics and predictors of adverse events in ACS including arrhythmias, cardiac arrest, and mortality as well as the impact of potassium disorders in this setting. Methods and results. Study I: We used data from the Swedish Web-system for Enhancement and Development of Evidence-based care in Heart disease Evaluated According to Recommended Therapies (SWEDEHEART) to assess predictors of in-hospital cardiac arrest in patients admitted with suspected non-ST-elevation ACS (NSTE-ACS). A risk-score model was developed including five variables: systolic blood pressure <100 mmHg, age ≥60 years, heart rate <50 or ≥100 bpm, ST-T abnormalities on the admission ECG, and Killip class ≥II. The risk-score model was temporally validated in SWEDEHEART and externally validated using data from the Myocardial Ischaemia National Audit Project (MINAP). Study II: Using SWEDEHEART and the Swedish Pacemaker and Implantable Cardioverter- Defibrillator (ICD) Registry, we identified patients without a prior ICD, who had undergone in-hospital coronary angiography and were discharged alive after myocardial infarction (MI). Associations between patient characteristics and out-of-hospital cardiac arrest (OHCA) as recorded in the Swedish Cardiopulmonary Resuscitation Registry within 90 days after discharge were assessed. The incidence of OHCA was low (0.29%) compared to previous studies. Six variables (male sex, age ≥60 years, estimated glomerular filtration rate [eGFR] <30 mL/min per 1.73 m2, Killip class ≥II, new-onset atrial fibrillation/flutter, and LVEF categorized as ≥50%, 40-49%, 30-39%, and <30%) were independently associated with OHCA and predicted OHCA as well as non-OHCA death better than an LVEF cut-off of <40% alone. Study III: Patients admitted with suspected ACS and registered in SWEDEHEART and the Stockholm CREAtinine Measurements (SCREAM) project were included. Associations between admission plasma potassium and in-hospital outcomes were assessed. In fully adjusted models, hyperkalemia was associated with mortality, while hypokalemia was associated with cardiac arrest and new-onset atrial fibrillation. No association was observed between potassium and second- or third-degree atrioventricular block. Results were not modified by discharge diagnosis (ACS subtype or non-ACS diagnosis) or baseline characteristics. Study IV: SWEDEHEART and SCREAM were used to identify patients discharged alive after MI. Associations between plasma potassium at discharge and outcomes within one year were assessed. Potassium and eGFR at discharge were found to be independent predictors of hyper- or hypokalemia within one year, which affected 36.5% of the patients. A U-shaped association was observed between discharge potassium and mortality within one year. Conclusion. A five-variable risk score can be used to predict in-hospital cardiac arrest in patients admitted with suspected ACS. In a contemporary cohort of MI patients, the incidence of OHCA within 90 days after discharge was low, but compared to an LVEF cut-off alone which is routinely used, five variables in addition to LVEF predicted OHCA better. Dyskalemias at admission are associated with in-hospital arrhythmic events and mortality across all ACS/non-ACS diagnoses regardless of baseline characteristics. Potassium disorders within the first year following MI are frequently encountered and potassium level and kidney function at discharge strongly predict their occurrence as well as one-year mortality.