Paced rhythm with retrograde P waves

Paced Anterograde and Retrograde P waves

ECG shows a wide QRS rhythm with LBBB pattern in I, aVL and V1. Axis is leftward and V6 shows negative QRS complexes, indicating pacing from the right ventricular apex. Pacemaker artefacts or spikes (S) can be seen on close scrutiny in V4-V6, just before the onset of the wide QRS complex. Anterograde P waves (P) are dissociated from the QRS complexes. Hence the basic rhythm was complete heart block which needed a pacemaker.

Retrograde P waves (P’) are seen after the paced QRS complex in the lead II rhythm strip, with a reasonable retrograde conduction time. This is an interesting situation in that anterograde complete heart block co-exists in the presence of fairly intact retrograde ventriculo-atrial conduction.