Inadvertent transvenous left ventricular pacing through an unsuspected atrial septal defect.

A 65-year-old male patient with a long standing history of chronic obstructive lung disease had permanent pacemaker implantation for symptomatic atrioventricular nodal blocks. Preoperative echocardiography showed dilated right heart chambers and moderate pulmonary arterial hypertension without any demonstrable intracardiac shunt. Postoperative twelve-lead ECG showed right bundle branch block configuration of paced complexes. This suggested left ventricular pacing which was confirmed by transthoracic echocardiography. Later, transoesophageal echocardiography showed the lead entering into left atrium from right atrium through a sinus venosus type of atrial septal defect. The patient refused any further intervention and continues to remain asymptomatic with stable pacing on aspirin-anticoagulant therapy at end of four years.