Abstract
Cor triatriatum sinistrum (CTs) represents approximately 0.1% of congenital heart disease. The presence of an abnormal, often fenestrated fibromuscular membrane is indicative of CTs and results in a subdivided left atrium that can obstruct pulmonary venous return leading to elevated pulmonary venous and pulmonary artery pressures. We describe a case of CTs presenting well into adulthood with the unusual association of atrial flutter. Given the rarity of CTs, this unique observation with atrial flutter is limited to this case report, but is meant to illustrate the ramifications of this arrhythmia even in this relatively simple congenital heart defect, as our patient's arrhythmia was refractory to treatment and behaved similarly to atrial flutter observed among patients with more complex heart defects. Accurate diagnosis of the abnormal atrial membrane in the setting of other cardiac defects is imperative because pulmonary venous obstruction can occur after surgery for the associated defects. An associated atrial arrhythmia complicates management further and remains an important cause of morbidity and mortality in patients with congenital heart defects regardless of whether or not they have had corrective heart surgery. Atrial flutter is particularly worrisome since its onset is usually associated with clinical deterioration in adult patients with congenital heart defects. Physicians need to be cognizant of this increasing new cardiac patient population particularly after the typical causes of atrial flutter (e.g., ischemic disease, electrolyte disturbances, thyroid disease, and mitral valve disease, etc) have been ruled out.