LAUSR

A 79-year old female presented with bradycardia and complaints of recent-onset recurrent pre-syncope and exertional breathlessness. Fig. 1A is the 12-lead ECG of this patient which revealed heart rate of 46 beats per minute (bpm) and a narrow QRS with a leftward axis (mean frontal QRS axis1⁄4 30 ). The diagnosis of Mobitz type II intra-Hisian or infra-Hisian AV block was considered on the basis of constant and normal PR intervals (160ms). She was taken for dual chamber pacemaker implantation with permanent His-bundle pacing [1,2]. The electrogram obtained by the lead at the His-bundle site revealed 2:1 infra-Hisian AV block (Fig. 1B). The pacemaker parameters set were: lower rate 60 bpm, sensed-AV delay 200ms, paced-AV delay 200ms, upper track rate (UTR) 130 bpm, post-ventricular atrial refractory period (PVARP) 340ms and mode switch at 171 bpm. Fig. 2 (Panels A and B) shows the 12-lead ECG on the first post-operative day. What could be the diagnosis?