Characterization of Arrhythmia-induced Cardiomyopathy

Prospective part Inclusion Criteria: * Diagnostic or suspicion of AiCM as presence of specified keyword in patient's file or as screened by colleagues of the internal medicine or cardiology clinics * Signed study consent Exclusion Criteria: * Patient's active refusal of the general consent of the University Hospital Basel * Age \<18 years old * Temporary exclusion criteria: Acute health condition such as myocardial infarction, patients presenting with a major trauma, a sepsis, patients shortly after cardiac surgery, and patients in shock (\>100 bpm, \<90 systolic BP, evidence of organ dysfunction). * Life expectancy \<1 year (palliative, terminal cancer) Retrospective part Inclusion Criteria: * Patients with a reduced left-ventricular ejection fraction (LVEF ≤50%) or a reduction of 15% in the ejection fraction (EF) between two echocardiographies and a concomitant diagnosis of any arrhythmia likely to lead to AiCM within one year before or after diagnosis of the reduced LVEF from 2010-2021 Exclusion Criteria: * Age \< 18 years old * Patient's active refusal of the general consent of the University Hospital Basel * Acute event clearly leading to an acutely reduced LVEF (massive type I myocardial infarction, cardiogenic shock from a coronary or myocardial etiology, septic shock leading to toxic myopathy, hypovolemic shock with reduced EF, cardiac arrest and/or need for resuscitation). * Patients with life expectancy \<1 year (palliative, terminal cancer)