Junctional (AV‑nodal) bradycardia
Definition and clinical importance
Junctional bradycardia is an escape rhythm originating from the atrioventricular (AV) nodal region that takes over when the sinoatrial (SA) node fails or SA‑to‑AV conduction is impaired. Typical junctional escape rates are 40-60 beats per minute.
In the emergency department it can present as symptomatic bradycardia, occur during acute coronary syndromes or reperfusion, or reflect reversible causes (drugs, electrolytes, ischaemia) or intrinsic conduction disease that may require permanent pacing.
Pathophysiology (concise)
The AV node has latent pacemaker activity; if sinus automaticity or conduction falls below the AV‑nodal rate, the junctional focus assumes pacing. Retrograde atrial activation may produce inverted P waves, absent P waves, or P waves occurring after the QRS.
Faster junctional firing produces an accelerated junctional rhythm (≈60-100 bpm) or junctional tachycardia (>100 bpm). (See Resuscitation Council UK guidance on escape rhythms.)
ECG features (12‑lead)
- Rate: usually 40-60 bpm for classic junctional escape rhythms.
- QRS: usually narrow unless there is pre‑existing intraventricular conduction delay or bundle branch block.
- P waves: absent, inverted in inferior leads, or occurring after the QRS due to retrograde atrial activation.
- PR interval: may be short if a P wave precedes the QRS.
- Rhythm: typically regular; look closely for AV dissociation to distinguish from sinus bradycardia.