Left bundle branch block

Evaluation

• ST Depression and T wave inversion are common
• QRS > 0.12 in limb leads
• Leads
  • Large and wide R waves — leads I, aVL, V5, and V6
  • Small R wave followed by deep S wave —leads II, III, aVF, V1–V3

LBBB

Differential Diagnosis

Wide-complex tachycardia

Assume any wide-complex tachycardia is ventricular tachycardia until proven otherwise (it is safer to incorrectly assume a ventricular dysrhythmia than supraventricular tachycardia with abberancy)

• Regular
  • Monomorphic ventricular tachycardia
  • PSVT with aberrant conduction:
    • PSVT with bundle branch block^
    • PSVT with accessory pathway
    • Atrial flutter with bundle branch block^
  • Sinus tachycardia with bundle branch block^
  • Accelerated idioventricular rhythm (consider if less than or ~120 bpm)
  • Metabolic
    • Hyperkalemia
    • Digoxin toxicity
    • Severe metabolic acidosis
• Irregular
  • Atrial fibrillation/atrial flutter with variable AV conduction AND bundle branch block^
  • Atrial fibrillation/atrial flutter with variable AV conduction AND accessory pathway (e.g. WPW)
  • Atrial fibrillation + hyperkalemia
  • Polymorphic ventricular tachycardia
    • Torsades de pointes
    • Nonsustained ventricular tachycardia

^Fixed or rate-related

See Also

• ECG (Main)
• Sgarbossa's Criteria
• STEMI equivalents

External Links

• emDocs - Left Bundle Branch Block in Myocardial Infarction: An Update

References

• Journal of Electrocardiology. Vol 43 (2010). 40-42.