ECG Case 055

Middle-aged patient presenting with drowsiness. BP 85/50. Pupils dilated. Interpret the ECG.

Describe and interpret this ECG


Main Abnormalities

This is a classic ECG of tricyclic antidepressant toxicity, demonstrating multiple characteristic abnormalities.

Signs of sodium-channel blockade

  • Broad QRS complexes (120 ms, or 3 small squares).
  • Positive R’ wave in lead aVR > 3 mm.
  • Prolonged PR interval (240 ms).
  • Long QT interval (> 1/2 the RR interval).
  • Brugada-like pattern in V1.

Signs of anticholinergic toxidrome

  • Sinus tachycardia (~ 110 bpm), with P waves embedded in each T wave.
R wave aVR
Positive R’ wave in aVR > 3mm

TCA long PR
P waves visible in V2 with long PR interval

Pseudo-Brugada pattern in V1
Pseudo-Brugada pattern in V1

This patient had taken a life-threatening overdose of dosulepin (a Tricyclic antidepressant TCA).

How to Spot Sodium-Channel Blockade

  • QRS prolongation (> 100ms or 2.5 small squares), typically measured in lead II.
  • A terminal or secondary R wave (R’ wave) in aVR > 3 mm.
  • An R’/S ratio in aVR > 0.7.

Prognostic Value of the ECG

In patients with TCA overdose, the degree of QRS prolongation correlates with the degree of clinical toxicity:

  • QRS width > 100 ms is predictive of seizures.
  • QRS width > 160 ms is predictive of cardiotoxicity (e.g. broad-complex dysrhythmias, hypotension).


The combination of PR prolongation and sinus tachycardia with TCA overdose often makes the P waves difficult to see, and may lead the rhythm to be incorrectly identified as VT. This patient needs bicarbonate and hyperventilation, not electricity and amiodarone!

The clinical significance of a TCA-induced Brugada ECG pattern remains controversial — i.e. is it purely a manifestation of severe sodium-channel blockade, or does it represent “unmasking” of underlying Brugada syndrome? These issues are discussed here.


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

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