Carbamazepine Cardiotoxicity

  • Massive carbamazepine overdose (>> 50mg/kg) is associated with cardiotoxicity due to fast sodium channel blockade.
  • This may be detectable on the ECG as subtle QRS widening or 1st degree AV block.
  • The ECG changes are not usually as dramatic as those seen in the context of TCA overdose.

ECG Examples

Example 1a

  • This first ECG was taken several hours after massive carbamazepine overdose (150-200 mg/kg), by which time the patient was beginning to manifest clinical signs of cardiotoxicity (hypotension requiring noradrenaline).
  • Carbamazepine level around that time was 33 mg/L.
  • There is subtle ECG evidence of fast sodium channel blockade: Note the QRS widening (135 ms), 1st degree heart block (PR 240ms) and small secondary R wave in aVR.

Example 1b 

  • This second ECG was taken several hours after intubation and treatment with hyperventilation (to pH 7.50) and haemofiltration.
  • Carbamazepine level is now down to 17 mg/L and haemodynamic instability has resolved.
  • Note the QRS duration and PR interval have now normalised, while the secondary R wave in aVR has reduced in amplitude.

 

Example 2

  • This ECG demonstrates more obvious cardiotoxicity following a massive carbamazepine overdose.
  • QRS complexes are broad and there is a large R’ wave in aVR.

 

Related Topics

Further Reading

Author Credits

References

  • Murray L, Daly F, Little M, Cadogan M. Toxicology Handbook (second edition). Elsevier, 2011.
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