Genetic Characterization of Patients With Arrhythmia-Induced Cardiomyopathy

Inclusion Criteria: * Presence of atrial fibrillation or atrial flutter not self-limited. * Performance of a cardiac imaging test with systolic function analysis (echocardiogram, magnetic resonance, CT scan) during the clinical course of the arrhythmia, exhibiting a left ventricular ejection fraction (LVEF) \<50%. In order for the test to be representative, the maximum time between the performance of the imaging test and the rhythm control procedure will be 3 months, in the absence of intervening cardiovascular events that may have caused a variation in LVEF. In the event that the patient had a previously known LVEF \<50%, the change with respect to this attributable to tachyarrhythmia has to be ≥10%. * Signature of informed consent. * Ability to understand and accept participation in the study. Exclusion Criteria: * Refusal of informed consent. * Legal or juridical incapacity. * Age \<18 years. * Life expectancy less than 1 year. * Impossibility of a follow-up of at least 6 months. * Presence of a ventricular rate \>140 beats per minute, limiting the validity of imaging measurements. * Presence of known factors causing systolic ventricular dysfunction: * Prior cardiomyopathy diagnosis. * Severe mitral or aortic valve disease. * Non-revascularizable ischemic heart disease. * Context of peri-resuscitation cardiopulmonary care. * Abusive alcohol consumption, defined as \>80 grams of ethanol or \>7 standard alcoholic beverages per day. * Active treatment with chemotherapeutic agents or radiation therapy to the thorax. * Known infection with Trypanosoma cruzi, Borrellia burgdorferi or other infectious agent causing cardiomyopathy.