Thymic Cyst-Induced Left Atrial Compression Associated with Atrial Fibrillation: A Unique Case Report

Abstract Background Atrial fibrillation (AF) is a prevalent and sustained arrhythmia in adults, with an estimated global prevalence of 37.5 million cases in 2017. While it primarily affects elderly individuals with structural heart disease (prevalence >10% after age 80), it can also occur in younger individuals, albeit with a much lower prevalence (<1% in those aged <40 years). Increasing knowledge about the pathophysiology of AF shows that in every patient there may be an underlying cause, which, although it cannot be discovered in all patients, should be explored, especially in young patients without risk factors. Case Summary We present a case of paroxysmal atrial fibrillation (PAF) in a 37-year-old female patient with no cardiovascular risk factors. The PAF was likely associated with an atypically located thymic cyst over the left atrium, which was incidentally discovered during an intracardiac echocardiogram (ICE) performed for pulmonary vein isolation. Subsequently, surgical cyst extraction was performed, resulting in improved episodes of atrial fibrillation. Discussion This case underscores the importance of considering uncommon anatomical variations when evaluating and managing AF. It also highlights the need for further research and understanding of Non-valvular AF, particularly in cases associated with thymic abnormalities, to better inform clinical decision-making and enhance patient outcomes.