20-year-old male presenting with seizures. BP 80/50. 


Describe and interpret this ECG


Main Abnormalities

What is the diagnosis?

Reveal answer

In the context of seizures and hypotension, the combination of…

  • QRS broadening > 100 ms
  • R’ wave in aVR > 3 mm

… is highly suggestive of poisoning with a sodium-channel blocking agent — e.g. tricyclic antidepressant.

The sinus tachycardia may be due to the anticholinergic effects of the TCA.


In the context of sodium channel blockade:

  • A QRS duration > 100 ms is predictive of seizures
  • A QRS duration > 160 ms is predictive of cardiotoxicity

This patient is already manifesting life-threatening toxicity and needs aggressive resuscitation, including:

  • Serum alkalinisation with NaHCO3 to reverse pH-dependent toxicity
  • Intubation and hyperventilation aiming for alkaline arterial pH (e.g. 7.45 to 7.55)
  • Seizure management with benzodiazepines
  • BP management with fluid boluses +/- pressors

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


  1. It looks to me more like a 2:1 AVB rather than a 1st degree. There are several leads but very clear in Lead II where it looks like a P wave right after the QRS morphology.

  2. True, it resembles 2:1 block, though the PP interval varies.
    My concern is different. Sinus rythm should have positive p waves in leads II, III, aVF and negative in aVR and this ECG in my opinion shows exactly the opposite. Could it be some ectopic atrial rythm than?

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