Mechanism:

• Block in the left bundle branch resulting in secondary (delayed) excitation of the left ventricle via the right ventricular myocardium

ECG characteristics:

• QRS ≥ 0.12s; discordance of the ventricular repolarization (ST segment and T wave)
  
• Ranging from left axis to marked left axis deviation
  
• QRS configuration : V1/2 – “QS,” V5/6- “R’”
  
• Turning point in V6: > 0.05 s

Etiology:

• CHD, acute myocardial infarction (poor prognosis), heart defects, hypertension, medications that may cause conduction delay, carditis, DCM

Treatment:

• Cessation of medications that may cause conduction delay
  
• In symptomatic patients (syncope) bradycardia: insertion of pacemaker (or in cases of an unknown cause of syncope: electrophysiological study to exclude ventricular arrhythmias)
  
• Conservative in the event of a lack of clinics

Differential diagnosis:

In preexisting bundle branch block:

• Atrial flutter with 3:1 conduction
  
• AV conduction delay with SVES
  
• 2nd or 3rd degree AV block
  
• Prolonged P wave duration with interatrial block

Mechanism:

• Delayed conduction at the AV node with additional block in the left bundle branch resulting in secondary (delayed) excitation of the left ventricle via the right ventricular myocardium

ECG characteristics:

• Complete left bundle branch block with delayed PQ interval (> 0.20 s)

Etiology:

• CHD, acute myocardial infarction (poor prognosis), cardiac defects, hypertension, medications that may cause conduction delay, carditis, DCM

Treatment:

• Cessation of medications that may cause conduction delay
  
• In symptomatic patients (syncope) bradycardia: insertion of pacemaker (or in cases of an unknown cause of syncope: electrophysiological study to exclude ventricular arrhythmias)
  
• Conservative in the event of a lack of clinics

Differential diagnosis:

In preexisting bundle branch block

• Atrial flutter with 3 :1 conduction
  
• AV conduction delay with SVES
  
• 2nd or 3rd degree AV block
  
• Prolonged P wave duration with interatrial block

Differential diagnosis:

In preexisting bundle branch block

• Atrial flutter with 3:1 conduction
  
• AV conduction delay with SVES
  
• 2nd or 3rd degree AV block
  
• Prolonged P wave duration with interatrial block