• Narrow QRS Complex
• Wide QRS Complex
• Ventricular Conduction Abnormality
• Differential Diagnosis
• Ventricular Rhythm

Narrow QRS Complex

• Occurs when the ventricles are activated through an intact
• ventricular conduction system
• Supraventricular impulse passes to the ventricles through the AV junction
• Then through the conduction system (His bundle branches)
• Very quickly depolarizes the ventricles within 0.1s
• Thus, in the case of an intact ventricular conduction system
• Narrow QRS complex (<0.1s)

Wide QRS Complex

• Occurs with a disruption of impulse conduction in the ventricles
• The ventricles are not depolarized only through the conduction system
• But also through the working myocardium
• The impulse spreads slowly through the myocardium
• Therefore, the ventricular depolarization will be slower (>0.1s)
• The EKG will show a wide QRS complex (>0.1s)
• The most common cause of ventricular conduction disruption is
• Bundle branch blocks (Left Bundle Branch Block (LBBB), Right Bundle Branch Block (RBBB))
• Hemiblocks (Left Anterior Fascicular Block (LAFB), Left Posterior Fascicular Block (LPFB))

Ventricular Conduction Abnormality

• It is a prolonged depolarization of the ventricles during activation by a supraventricular impulse
• QRS width is > 0.1s
• Mechanisms of ventricular conduction abnormality:
• Disruption of the ventricular conduction system
• Bundle branch blocks (Left Bundle Branch Block (LBBB), Right Bundle Branch Block (RBBB))
• Delayed ventricular myocardial depolarization
• Hyperkalemia
• Prolonged depolarization due to myocardial hypertrophy
• Left Ventricular Hypertrophy

Ventricular Rhythm

• In ventricular rhythm, impulses originate
• From an ektopic ventricular focus
• The ventricles are then depolarized from the ventricular focus
• SLOWLY through the myocardium, not through the conduction system
• Results in wide QRS complexes >0.12s (rarely >0.1s)
• Most common causes of ventricular depolarization from an ectopic focus
• Ventricular Tachycardia
• Accelerated Ventricular Rhythm
• Ventricular Rhythm
• Pacemaker
  
  
• If the ventricles are depolarized from an ectopic ventricular focus
• This is not considered a conduction disturbance
• In conduction disturbance, the ventricles must be
• depolarized by a supraventricular impulse

Left Bundle Branch Block (LBBB)

• Wide QRS ≥ 0.12s (≥ 3 small squares)
• Deep S (V1)
• rS configuration
• Dominant R (V6)
• Discordance
• QRS complexes are oriented oppositely to T waves (negative QRS and positive T waves)
• Best evaluated in (V1-V3)
• Left Bundle Branch Block (LBBB)
• It is among the most common causes of ventricular conduction disturbances