Cor triatriatum sinistrum: a rare congenital cardiac anomaly presenting in an adult with chronic atrial fibrillation.

Cor triatriatum is a rare congenital cardiac anomaly in which the left atrium is divided into proximal (dorsal or upper) and distal (ventral or lower) chambers by a fibromuscular septum. The upper chamber receives the pulmonary veins and the lower chamber contains the atrial appendage and the mitral valve. The 2 chambers communicate through a defect in the membrane. Cor triatriatum is often associated with other congenital cardiac anomalies. Most frequently, the upper chamber communicates with the right atrium through a patent foramen ovale or atrial septal defect, and the clinical symptoms simulate anomalous pulmonary venous return. Less commonly, the foramen ovale communicates with the distal chamber and the clinical features mimic mitral stenosis. When cor triatriatum is the only abnormality, the clinical findings are also similar to mitral stenosis with development of pulmonary hypertension and subsequent right ventricular hypertrophy and atrial enlargement. The diagnosis is usually made in infancy or childhood, and the lack of treatment results in death in 75% of patients. We report the case of a woman who presented much later in life. The patient was a 57-year-old female with a clinical history of chronic atrial fibrillation who presented to the emergency department because of a "funny sensation" in her chest, though she denied chest pain, nausea, vomiting, or diaphoresis. EKG revealed atrial fibrillation with a rapid ventricular response and a tachycardic rate of 157. She had a therapeutic level of digoxin, and cardiac enzymes were normal. The patient was admitted and placed on Cardizem drip. Serial EKGs remained normal and heart rate control was achieved. On hospital day 2, the patient became dyspneic and cyanotic. She went into cardiac arrest and died.Autopsy revealed cardiomegaly (610 g) with 4-chamber dilatation. A septum divided the left atrium into 2 chambers. The defect in the dividing membrane measured 1 cm in diameter. No other congenital defects were noted. The large size of the defect in the membrane likely accounted for the late onset of symptoms that allowed this patient to survive into adulthood without previous diagnosis or surgical intervention (which is usually required in childhood).