• Phase 3 of the Action Potential
• Action Potential and Refractory Period
• ECG and Phase 3 Block
• Ashman's Phenomenon
• Refractory Period and RR Interval
• Ventricular Extrasystole and Ashman's Phenomenon

Phase 3 of the Action Potential

• Action potential (impulse) is a rapid change in the electrical voltage of cardiomyocytes
• It arises due to changes in the concentration of intracellular and extracellular ions
• The action potential propagates
• Quickly through the conduction system
• Slowly through the working myocardium

Phase 3 of the action potential

• On the ECG, it is seen as the T wave (ventricular repolarization)
• It is the relative refractory period (RRP)
• If an impulse arrives at a cardiomyocyte (in the conduction system or the myocardium) during the RRP
• Then this impulse will be blocked

ECG and Phase 3 Block

• The right bundle branch (RBB) has a longer absolute refractory period (ARP)
  • than the left bundle branch (LBB)

Physiological Conduction

• Supraventricular impulse
• Passes through the bundle branches
• outside of RRP
• The impulse is not blocked
• QRS complexes are narrow and have a uniform shape

Aberrant Conduction

• Supraventricular extrasystole
• Occurred during the RRP of the right bundle branch
• The extrasystole is blocked only in the right bundle branch
• QRS complex is wide and has the shape of a right bundle branch block
• The impulse is conducted only through the left bundle branch

Refractory Period and RR Interval

• Refractory period prolongs with the RR interval
• This is the fundamental principle of Ashman's phenomenon

Ashman's Phenomenon and Atrial Fibrillation

• Left shows atrial fibrillation
• The RR interval is nearly constant
• Ashman's phenomenon is not present
• The supraventricular impulse is not blocked in the ventricular conduction system
• Right shows atrial fibrillation with Ashman's phenomenon
• After a prolonged RR interval, a short RR interval follows
• The prolonged RR interval prolongs the subsequent refractory period of the conduction system
• The supraventricular impulse of the short RR interval
• Reaches the conduction system during the refractory period and gets 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

Ashman's Phenomenon and Atrial Fibrillation

• Atrial Fibrillation
• After a long RR interval follows a short RR interval
• The short RR interval ends with aberrant conduction showing the pattern of a right bundle branch block

Ventricular Extrasystole and Ashman's Phenomenon

• Ventricular Extrasystole is sometimes mistaken for Ashman's Phenomenon
• Because both conditions produce a wide QRS complex

• QRS Width
• Ventricular Extrasystole (VES) has a wider QRS
• Because the ventricles are slowly activated from an ectopic focus through the myocardium
• In Ashman's Phenomenon, part of the ventricles are activated faster through the conduction system
• Therefore, the QRS is narrower
• QRS Shape
• VES has a bizarre QRS
• Because it originates in an ectopic focus somewhere in the ventricle
• In Ashman's Phenomenon, part of the ventricles are activated through the bundle branch (most often the left)
• Therefore, the QRS has the pattern of a right bundle branch block (RBBB) or a left bundle branch block (LBBB)
• Coupling Interval (the interval between the extrasystole and the preceding QRS)
• In VES, it is the same
• Because each VES is from the same focus
• (rarely, VES can originate from 2 foci, resulting in 2 different coupling intervals)
• Ashman's Phenomenon has a variable coupling interval
• Because the supraventricular impulse is blocked randomly in the refractory period
• Compensatory Pause
• VES has a complete compensatory pause
• Because the impulse from the VES retrogradely blocks the supraventricular impulse in the conduction system
• However, the compensatory pause is assessed during a regular sinus rhythm, not during atrial fibrillation

Ashman Phenomenon and Atrial Fibrillation

• Atrial fibrillation on a 12-lead ECG
• After a long RR interval (green arrow), a short RR interval (red arrow) follows
• The short RR interval is terminated by aberrant conduction (blue arrow)
• with the pattern of a right bundle branch block (RBBB)
• Typical RBBB pattern in leads V1 and V6

Ashman Phenomenon and Atrial Fibrillation

• Atrial fibrillation on a 12-lead ECG
• After a long RR interval, a short RR interval follows
• The short RR interval is terminated by aberrant conduction with the pattern of a right bundle branch block (RBBB)
• Typical RBBB pattern in leads V1 and V6