Accelerated Junctional Rhythm

Background

  • Accelerated junctional rhythm (AJR) occurs when the rate of an AV junctional pacemaker exceeds that of the sinus node.
  • This situation arises when there is increased automaticity in the AV node coupled with decreased automaticity in the sinus node.

Causes

  • Digoxin toxicity (= the classic cause of AJR)
  • Beta-agonists, e.g. isoprenaline, adrenaline
  • Myocardial ischaemia
  • Myocarditis
  • Cardiac surgery

Terminology

Junctional rhythms are arbitrarily classified by their rate:

  • Junctional Escape Rhythm: 40-60 bpm
  • Accelerated Junctional Rhythm: 60-100 bpm
  • Junctional Tachycardia: > 100 bpm

They may also be classified by their aetiology:

  • 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

Accelerated Junctional Rhythm

ECG Features of AJR

  • Narrow complex rhythm; QRS duration < 120ms (unless pre-existing bundle branch block or rate-related aberrant conduction).
  • Ventricular rate usually 60 – 100 bpm.
  • Retrograde P waves may be present and can appear before, during or after the QRS complex.
  • Retrograde P waves are usually inverted in the inferior leads (II, III, aVF), upright in aVR + V1.
  • AV dissociation may be present with the ventricular rate usually greater than the atrial rate.
  • There may be associated ECG features of digoxin effect or digoxin toxicity.

Differential Diagnosis

Rapid AJR  may be difficult to distinguish from re-entrant junctional tachycardias such as AVNRT or AVRT.

  • Irregularity of rhythm and heart-rate variability are suggestive of automatic junctional tachycardia.
  • Automatic junctional tachycardia is typically non-responsive to vagal manoeuvres — 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.

  • The presence of fusion or capture beats indicates a ventricular rather than junctional focus.

ECG Example

Accelerated Junctional Rhythm

  • Narrow complex tachycardia at 115 bpm.
  • Retrograde P waves — inverted in II, III and aVF; upright in V1 and aVR.
  • Short PR interval (< 120 ms) indicates a junctional rather than atrial focus.

 

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References

  • Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice. 6th Edition. Saunders Elsevier 2008.
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
  • Mattu A, Brady W. ECGs for the Emergency Physician 2, BMJ Books 2008.
  • Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.

Further Reading

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