Junctional Escape Rhythm

ECG features of Junctional Escape Rhythm

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Mechanism

Pacemaker cells are found at various sites throughout the conducting system, with each site capable of independently sustaining the heart 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.

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Causes

Conditions leading to the emergence of a junctional or ventricular escape rhythm include:

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ECG Examples

Example 1

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

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Example 2

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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

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Advanced Reading

Online

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

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LITFL Further Reading

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