left bundle branch block

The diagram below shows the typical features of left bundle branch block (LBBB):

One of the most common ways to remember the difference between LBBB and RBBB is WiLLiaM MaRRoW

• in LBBB there is a 'W' in V1 and a 'M' in V6
• in RBBB there is a 'M' in V1 and a 'W' in V6

Left bundle branch block - e Image used on license from Dr Smith, University of Minnesota

ECG showing typical features of LBBB

New LBBB is always pathological. Causes of LBBB include:

• myocardial infarction
  • diagnosing a myocardial infarction for patients with existing LBBB is difficult
  • rhe Sgarbossa criteria can help with this - please see the link for more details
• hypertension
• aortic stenosis
• cardiomyopathy
• rare: idiopathic fibrosis, digoxin toxicity, hyperkalaemia