A 60 year old woman with hypertension.

Atrial fibrillation with pre-existing left bundle branch block

• Sometimes this can be confused with ventricular tachycardia but closer inspection can identify the irregularity.
• Irregularly irregular rhythm - suggesting AF.
• Features of typical left bundle branch block
  • wide QRS >120 ms (3 small squares)
  • no secondary R wave in lead V1
  • no lateral Q waves