Definition of Junctional Escape Rhythm
- A junctional rhythm with a rate of 40-60 bpm.
- QRS complexes are typically narrow (< 120 ms).
- No relationship between the QRS complexes and any preceding atrial activity (e.g. P-waves, flutter waves, fibrillatory waves).
Mechanism of Junctional Escape Rhythm
The rate of spontaneous depolarisation of pacemaker cells decreases down the conducting system:
- SA node (60-100 bpm)
- Atria (< 60 bpm)
- AV node (40-60 bpm)
- Ventricles (20-40 bpm)
Under normal conditions, subsidiary pacemakers are suppressed by the more rapid impulses from above (i.e. sinus rhythm). Junctional and ventricular escape rhythms arise when the rate of supraventricular impulses arriving at the AV node or ventricle is less than the intrinsic rate of the ectopic pacemaker.
Atrial fibrillation with 3rd degree AV block and a junctional escape rhythm (“regularised AF”)
- Coarse atrial fibrillation (irregular baseline with atrial complexes at rate > 400 bpm).
- Regular narrow complex rhythm at 60 bpm.
- The combination of atrial fibrillation with a regular rhythm (“regularised AF”) indicates that none of the atrial impulses are conducted to the ventricles, i.e. complete heart block is present.
- The narrow complex rhythm is therefore a junctional escape rhythm.
- Regularised AF is characteristically seen as a consequence of digoxin toxicity.
Terminology of junctional rhythms
- Junctional bradycardia = junctional rhythm at a rate of < 40 bpm.
- Junctional escape rhythm = junctional rhythm at a rate of 40-60 bpm.
- Accelerated junctional rhythm = junctional rhythm at 60-100 bpm.
- Junctional tachycardia = junctional rhythm at > 100 bpm.
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Hampton, JR. The ECG In Practice, 6e
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
- Wagner, GS. Marriott’s Practical Electrocardiography 12e
- Chan, TC. ECG in Emergency Medicine and Acute Care
- Mattu, A. ECG’s for the Emergency Physician
LITFL Further Reading
- ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis –alphabetical diagnostic approach to the ECG
- ECG CLINICAL CASES — ECG’s placed in clinical context with a challenging Q&A approach
- 100 ECG Quiz — Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS — the best of the rest
- LITFL ECG IMAGE Database — Searchable database of LITFL ECG’s
- ECG and Cardiology Eponymous Syndromes — Cheats guide to eponymous emancipation
- ECG Exam Template — a framework for answering ECG exam questions.