Ventricular Escape Rhythm

AKA “Idioventricular escape rhythm”

Definition

• A ventricular rhythm with a rate of 20-40 bpm.
• QRS complexes are broad (≥ 120 ms) and may have a LBBB or RBBB morphology.

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.

Causes

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

• Severe sinus bradycardia
• Sinus arrest
• Sino-atrial exit block
• High-grade second degree AV block
• Third degree AV block
• Hyperkalaemia
• Drugs: beta-blocker, calcium-channel blocker or digoxin poisoning

 

ECG Examples

Example 1 – Sinus arrest with a ventricular escape rhythm

The ECG shows:

• Sinus pause / arrest (there is a single P wave visible on the 6-second rhythm strip).
• Broad complex escape rhythm with a LBBB morphology at a rate of 25 bpm.
• The LBBB morphology (dominant S wave in V1) suggests a ventricular escape rhythm arising from the right bundle branch.

 

Example 2 – Complete heart block with a ventricular escape rhythm 

The ECG shows:

• Sinus rhythm with 3rd degree AV block.
• Broad complex escape rhythm at around 27 bpm.
• The RBBB (dominant R wave in V1) + left posterior fascicular block (right axis deviation) morphology suggests a ventricular escape rhythm arising from the left anterior fascicle.

 

Example 3 -  Complete heart block with a ventricular escape rhythm 

The ECG shows:

• Sinus rhythm with 3rd degree AV block.
• Extremely slow broad complex escape rhythm (around 15 bpm).
• The RBBB morphology (dominant R wave in V1) indicates a ventricular escape rhythm arising somewhere within the left bundle branch.

 

Related Topics

• Junctional Escape Rhythm

Further Reading

• ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
• ECG Reference Sites on the WEB – the best of the rest

Author Credits

References

• Chan TC, Brady WJ, Harrigan RA, Ornato JP and Rosen PR. ECG in Emergency Medicine and Acute Care. Elsevier 2005.
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice (6th edition), Saunders 2008.