Discordant Junctional Beats and Preexcitation

An 18-year-old woman with Down syndrome and ventricular preexcitation was referred to our center for electrophysiological evaluation. She had no structural heart disease, and her 12-lead ECG showed minimal preexcitation. After obtaining an informed consent, an electrophysiology study was performed under conscious sedation. Via bilateral femoral veins, multipolar diagnostic catheters were introduced and positioned at the His bundle region and coronary sinus. A roving quadripolar catheter was positioned alternatively in the right ventricle, the right atrium appendage, and successively was used for mapping. At the beginning of the procedure, nonpreexcited junctional beats were recorded, a phenomenon compatible with a typical atrioventricular accessory pathway (AP). However, a comprehensive electrophysiology study confirmed the presence of an innocent fasciculoventricular pathway (FVP), showing minimal and fixed preexcitation (ie, the His–ventricular interval) during multisite atrial pacing and at different pacing rates. The effective refractory period …