ECG Case 055

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

TOP 100 ECG QUIZ LITFL 055

Describe and interpret this ECG

ECG ANSWER and INTERPRETATION

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).

CLINICAL PEARLS

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.


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 |

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