• Block in Phase 3
• ECG and Block in Phase 3
• Ashman's Phenomenon
• Aberrant Retrograde Bundle Branch Block

Block in Phase 3

Block in Phase 3

• Occurs when a supraventricular impulse reaches a part of the ventricular conduction system
• in the 3rd phase of the action potential (RRP - Relative Refractory Period)
• This supraventricular impulse gets blocked in that part of the conduction system
  
  
• It is the most common cause of aberrant conduction
• It is a temporary disorder of the ventricular conduction system
• It is an abnormal conduction (action potential) through the ventricular conduction system
• It is a physiological response of the conduction system to overload
  
  
• On an ECG, it can appear as
• Right Bundle Branch Block
• It is the most common manifestation of a block in phase 3
• Because the right bundle has a longer absolute refractory period (ARP) than the left
• Left Bundle Branch Block
• Complete AV Block
• Fascicular Block (anterior or posterior)

Ashman's Phenomenon

• Ashman's phenomenon is a phase 3 block that follows a prolonged RR interval
• If a supraventricular impulse travels through the bundle branch during the refractory period, it will be blocked
• The refractory period lengthens with the RR interval
• This is the basic principle of Ashman's phenomenon

Ashman's Phenomenon and Atrial Fibrillation

• Left side shows atrial fibrillation
• The RR interval is almost consistent
• Ashman's phenomenon is not present
• The supraventricular impulse is not blocked in the ventricular conduction system
• Right side shows atrial fibrillation with Ashman's phenomenon
• Following a prolonged RR interval, a short RR interval occurs
• The prolonged RR interval lengthens the subsequent refractory period of the conduction system
• The supraventricular impulse of the short RR interval
• Reaches the conduction system during its refractory period and is blocked
• On the ECG, a QRS complex appears with the pattern of a right bundle branch block (RBBB)
• Because the right bundle has a longer refractory period than the left

Aberrant Retrograde Bundle Branch Block and Ashman's Phenomenon

• Atrial fibrillation
• Ashman's phenomenon
• After a long RR interval, a short RR interval follows
• The short RR interval ends with aberrant conduction showing a pattern of right bundle branch block (rsR)
• It can occasionally trigger Aberrant Retrograde Bundle Branch Block (ARTB):
• The impulse from the first aberrant QRS turns around in the ventricles
• and retrogradely blocks the next impulse in the bundle branch