Overview
- Tachyarrhythmia caused by increased automaticity in his bundle pacemaking cells
- Occurs when the rate of an AV junctional pacemaker exceeds that of the sinus node
- Arises when there is increased automaticity in the AV node coupled with decreased automaticity in the sinus node
Junctional rhythm classification by rate
- Junctional escape rhythm: 40-60 BPM
- Accelerated junctional rhythm: 60-100 BPM
- Junctional tachycardia: >100 BPM
Junctional rhythm classification by etiology
- Automatic junctional rhythms (e.g. AJR) = due to enhanced automaticity in AV nodal cells
- Re-entrant junctional rhythms (e.g. AVNRT) = due to re-entrant loop involving AV node
ECG Features
- Regularity: regular
- Ventricular rate: 60–100 BPM
- QRS duration: normal (< 120 ms), unless pre-existing bundle branch block or rate-related aberrant conduction
- Retrograde P waves may be present and can appear before, during, or after the QRS complex; usually inverted in the inferior leads (II, III, aVF), upright in leads aVR and V1
- AV dissociation may be present with the ventricular rate usually greater than the atrial rate
- May be associated ECG features of digoxin effect or toxicity
Causes
- Drugs: digoxin toxicity (classic cause of AJR), beta-agonists (e.g. isoprenaline, adrenaline)
- Others: myocardial ischemia, myocarditis, cardiac surgery
Differential Diagnosis
- Rapid AJR may be difficult to distinguish from re-entrant junctional tachycardias (e.g. AVNRT, AVRT)
- Irregularity of rhythm and heart-rate variability are suggestive of automatic junctional tachycardia
- Automatic junctional tachycardia is typically non-responsive to vagal maneuvers; there may be some transient slowing of the ventricular rate, but reversion to sinus rhythm will not occur
- AJR with aberrant conduction may be difficult to distinguish from accelerated idioventricular rhythm; presence of fusion or capture beats indicates a ventricular rather than junctional focus
