• Supraventricular Impulse
• Ventricular Conduction and QRS Complex
• Action Potential and ECG
• Action Potential and Refractory Period
• Aberrant Conduction
• ECG and Aberrant Conduction

Supraventricular Impulse

• It is an impulse that occurs during the heart rhythm
• above the ventricles (somewhere in the atria or in the AV junction)
• Supraventricular impulse
• Passes to the ventricles through the AV junction
• The AV junction is the only electrical connection between the atria and ventricles
• Unless an accessory pathway is present (WPW syndrome)
• If the AV junction is interrupted, a third-degree AV block occurs

Action Potential and ECG

• 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
• Action potential propagates
• Quickly through the conduction system
• Slowly through the working myocardium

ECG (lead V6) and Action Potential

• The QRS complex represents ventricular depolarization
• During the QRS complex, a depolarization wave spreads through the ventricles
• The ST segment is an isoelectric line
• During phase 2 of the action potential, the entire myocardial wall is depolarized (-), no electrical vector is generated
• The T wave represents ventricular repolarization
• The electrical vector during repolarization has the same direction as during depolarization
• However, repolarization takes longer, so the T wave is wider than the QRS complex
• The QT interval corresponds to one electrical cardiac cycle:
• Ventricular depolarization and repolarization
• The P wave represents atrial depolarization
• The action potential of the P wave is not shown in the figure
• Atrial repolarization is hidden within the QRS complex

Aberrant Conduction

• It is a temporary disorder of the ventricular conduction system
• It is an abnormal conduction of the impulse (action potential) through the ventricular conduction system
• This is a physiological response of the conduction system to overload (by frequency)
• Causes include:
• Slowed conduction through the conduction system
• Blockage in the conduction system
• On the ECG, it appears as a wide QRS complex (>0.12s)
  
  
• The most common mechanisms of aberrant conduction are:
• Phase 3 Block (Tachycardia-dependent block)
• Ashman phenomenon
• Aberrant retrograde bundle branch block
• Phase 4 Block (Bradycardia-dependent block)

Aberrant Conduction and Sinus Rhythm

• Sinus rhythm
• Heart rate: 75/min
• Continuous lead II (the lowest lead)
• The 6th and 9th QRS complexes are due to atrial extrasystole
• In other leads, the QRS complex has the morphology of a right bundle branch block
• Atrial extrasystoles
• Pass through the right bundle branch during ARP (or RRP)
• Thus, they are blocked in the right bundle branch, and the ventricles are activated only through the left bundle branch
• This is an example of aberrant conduction (abnormal conduction of the impulse through the ventricular conduction system)