A puzzling overnight change in the QRS morphology

Pacemakers set in a bipolar pacing mode often result in no discernible spikes on surface 12‑lead ECG registrations. In this situation, left axis deviation combined with wide QRS can help to identify the paced ECG morphology. We present a case of a non-pacemaker dependent patient whose normal atrioventricular conduction also appeared as atypical left axis deviation with wide QRS on the ECG. These two depolarization-repolarization morphologies, and the switch between the two raised differential diagnostic questions. The case also illustrates a paced ECG demonstrating the concept of Littmann: a close relationship between leads V2 and aVL.