Ventricular Escape Rhythm

Definition

Ventricular Escape Rhythm: A ventricular rhythm with a rate of 20-40 bpm.

• QRS complexes are broad (≥ 120 ms) and may have a LBBB or RBBB morphology.
• Also known as Idioventricular escape rhythm

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

• 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

• 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

• 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

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest

Advanced Reading

• Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
• Wagner GS. Marriott’s Practical Electrocardiography 12e
• Chan TC. ECG in Emergency Medicine and Acute Care
• Rawshani A. Clinical ECG Interpretation
• Mattu A. ECG’s for the Emergency Physician
• Hampton JR. The ECG In Practice, 6e