• Left Bundle Branch Block
• ECG and LBBB
• STEMI and LBBB
• Sgarbossa Criteria
• ECG and Acute STEMI with LBBB
• ECG LBBB vs. LBBB + STEMI
• LBBB and Old Anteroseptal STEMI

Left Bundle Branch Block

• LBBB occurs mainly due to a degenerative process in the conduction system
• Prevalence of LBBB in the population:
• In the 50s, LBBB affects 1% of people
• In the 80s, LBBB affects 17% of people
• Main Left Bundle Branch (LBB)
• Supplied by branches from the LAD
• Often also collateral branches from the RCA and LCx
• LBBB affects the depolarization of the left ventricle
• The entire left ventricle is activated from the right bundle branch
• LBBB can also occur in STEMI infarction due to a proximal occlusion of the LAD
• Up to 50% of patients with LBBB and STEMI
• do not have typical angina symptoms (chest pain)
  
  
• Newly developed LBBB with symptoms of infarction
• is considered a equivalent to STEMI
• The problem is whether the LBBB is newly developed or old?
• Infarction can occur:
• Simultaneously with LBBB
• In the context of pre-existing LBBB

STEMI and LBBB

• In the case of a proximal occlusion, of the LAD
• anterior STEMI (antero-lateral)
• and almost always LBBB
• The left bundle branch is supplied
• through proximal branches of the LAD, and often also through collaterals from the RCA and LCx
• In proximal LAD occlusion, LBBB may not always occur
• Due to collateral supply from the RCA and LCx
  
  
• STEMI can occur:
• Simultaneously with LBBB
• In the context of pre-existing LBBB

ECG and Acute STEMI with LBBB

• 1. Concordant ST elevation > 1mm (V4-V6, aVL, I)
• In leads with positive QRS complex
• 5 points
• 2. Discordant ST elevation ≥ 5mm (V1-V3)
• Or ST elevation > 25% of S wave depth
• In leads with negative QRS complex
• 2 points
• 3. Concordant ST depression > 1mm (V1-V3)
• In leads with negative QRS complex
• 3 points
  
  
• If the total points ≥ 3 (Sgarbossa criteria are met)
• Then the patient has STEMI in the context of
• LBBB
• or ventricular pacing

• ST elevation = 3.2mm
• S wave depth = 10mm
• 3.2/10 = 0.32 (32%)
• ST elevation is 32% of S wave depth
• 2nd criterion is positive
• (2 points)

LBBB and Old Anteroseptal STEMI

• Septal Q wave arises from activation of the septum in lateral leads (V5-V6, I, aVL)
• The Tawar branches are intact
• The septum is activated from left to right (toward the lateral leads)
• The septum is activated from the left Tawar branch
• LBBB without infarction does not create a Q wave in the lateral leads
• Because the septum is activated from right to left (toward the lateral leads)
• The septum is activated from the right Tawar branch (left is interrupted)
• If a Q wave is present in the lateral leads (V5-V6, I, aVL) in the context of LBBB
• Then this Q wave is due to the electrical window after a septal infarction
• Most commonly after an antero-septal infarction (due to proximal RIA occlusion), where LBBB also occurs
• Infarction Q wave occurs approximately 9 hours after STEMI

Acute STEMI and LBBB

• Left Bundle Branch Block
• Concordant ST elevation > 1mm (V4-V6, aVL, I)
• No
• Disconcordant ST elevation ≥ 5mm (V1-V3)
• No
• Concordant ST depression > 1mm (V1-V3)
• Yes (3 points)
• The patient has an STEMI infarction in the context of LBBB

Acute STEMI and LBBB

• Left Bundle Branch Block
• Concordant ST elevation > 1mm (V4-V6, aVL, I)
• Yes - V4 (5 points)
• Disconcordant ST elevation ≥ 5mm (V1-V3)
• Yes - V2 (2 points)
• Concordant ST depression > 1mm (V1-V3)
• No
• The patient has an STEMI infarction in the context of LBBB