QS Study

Ventricular Escape

Stimulation of parasympathetic (vagus) nerve decreases the rate of a rhythm of the sinus node and also decreases the notability of AV Junctional fiber slowing the transmission of cardiac impulse into the ventricle. It may be seen in patients with sinus node dysfunction or AV block with inadequate junctional escape rhythm.

Very strong stimulation of the vagi can totally stop the rhythmic contraction of SA node or completely block transmission of cardiac impulse through the A-V junction. As a result, ventricles stop beating for 5-20 seconds. But then some points in Purkinje fibers, typically in the ventricular septal portion of AV bundle develops a rhythm of its own and causes ventricular contraction at a rate of 15 to 40 beats per minute. This is called ventricular escape.

Fig: Ventricular Escape graph 

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

A ventricular escape beat may occur after a sinus pause or as a result of the following conditions:

  • hypoxia
  • excessive vagal effect on SA node/parasympathetic stimulation
  • cardiac: proximal right coronary artery disease that often causes a sinus pause