PMC5528920_01
(a) 12-lead ECG recorded upon admission to our hospital and (b) electrogram (EGM) recorded by the pacemaker in the right ventricle, showing a frequency of 75 bpm. As seen on the marker channel, no pacing occurred, and all QRS were sensed by the ventricular lead (VS: ventricular sense). Only one atrial sense is shown on this part of the marker channel (Ab: Atrial sense in postventricular atrial blanking period). It has to be noted that this printout was made after amiodarone and lidocaine therapy were already started, which explains the low atrial frequency (17 bpm) detected in the atrial-derived EGM (not shown) at that time.
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The ECG (Figure 1(a)) was initially interpreted as atrial fibrillation (122 bpm) with aspects of a right bundle branch block, yet it already appeared atypical to the treating physicians at that time. This, together with the fact that there was no stimulation by the pacemaker, led to the conclusion that the current rhythm was of ventricular origin (Figure 1(b)).