A case of cor triatriatum with an abnormal P wave: the pacemaker action from the specialized tissue in the abnormal septum.

A boy presented with an abnormal P wave shown on an electrocardiogram (ECG) checkup at school. An echocardiogram and contrast-enhanced computed tomography (CT) showed cor triatriatum with a slit-like opening between the accessory chamber and the left atrium located along the interatrial septum. The boy underwent open heart surgery for excision of the anomalous membrane, and a postoperative ECG showed normal P waves. The excised tissue was examined immnunohistopathologically using antihyperpolarization-activated cyclic nucleotide-gated potassium channel 4 (HCN4) antibody and other staining. The authors confirmed the existence of cells positive to HCN4, indicating that they were sinoatrial node cells or at least cells with electrical automaticity.