Clinical problem solving: Maneuvering around a narrow complex tachycardia in a patient with Mustard repair for transposition of the great arteries

Case report The patient was initially palliated with balloon atrial septostomy before undergoing Mustard repair at age 1. The subsequent course was complicated by both inferior vena cava baffle stenosis and obstruction to pulmonary venous flow requiring surgical correction. Following these procedures, a dual-chamber permanent pacemaker was implanted for bradycardia at age 22 owing to presumed sinus node dysfunction. Echocardiography confirmed satisfactory systemic (morphologic right) ventricular function with ventriculoarterial discordance noted. There was no evidence of recurrent baffle obstruction. Echocardiographic imaging was consistent with an excellent hemodynamic result from an atrial switch repair for d-TGA. Owing to ongoing symptoms despite sotalol therapy, the patient was referred for an electrophysiology (EP) study. Catheter positions at EP study are shown in Figure 1A. The decapolar catheter was positioned in the systemic atrial appendage because the coronary sinus could not be identified and often empties into the pulmonary venous atrium (detailed surgical notes were not available to confirm this). Figure 1B shows a permanent pacemaker rhythm strip from a typical tachycardia episode (rate 180 beats/min). The electrocardiogram (ECG) during sinus rhythm is shown in