An interesting response to His-synchronous ventricular stimulation: What is the mechanism of this supraventricular tachycardia?

A20?year?old male with an implantable cardioverter?defibrillator(ICD) that had been implanted 7 years ago due to recurrent and failedablation for fascicular left ventricular tachycardia was referred forseveral inappropriate shocks and an elective replacement indicatoralert. He had no personal or family history of sudden cardiac death orinherited disorders that can cause arrhythmia.