20-year old female presenting with palpitations and presyncope, BP 75/50

Describe and interpret this ECG


Main Abnormalities:

  • Irregularly irregular broad complex tachycardia
  • Extremely rapid ventricular rates — up to 300 bpm in places (RR intervals as short as 200ms or 1 large square)
  • Beat-to-beat variability in the QRS morphology, with subtle variation in QRS width

Explanation of ECG Findings:

  • Irregularly irregular rhythm is consistent with atrial fibrillation
  • There is a left bundle branch block morphology to the QRS complexes
  • However, the ventricular rate is far too rapid for this to be simply AF with LBBB
  • The rates of 250-300 bpm and the variability in QRS complex morphology indicate the existence of an accessory pathway between the atria and ventricles


  • Broad complex irregular tachycardia at very rapid rates? -> Suspect AF with WPW!
  • These patients can rapidly become haemodynamically unstable
  • The options for chemical cardioversion are very limited, favouring DC cardioversion

We would recommend immediate DC cardioversion in this patient. Our approach would be:

  • Fluid load with 0.5 – 1L crystalloid bolus
  • Add in a push-dose vasopressor to elevate the BP (e.g. Metaraminol 0.5 – 1mg IV)
  • Sedate with something that has minimal effects on BP (e.g. fentanyl or ketamine in cautious doses)
  • Shock at 200J biphasic. Consider using an AP pad position for maximal 1st shock success

TOP 100 ECG Series

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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