Carbamazepine Cardiotoxicity Overview
- 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.
- 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.
- 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.
- This ECG demonstrates more obvious cardiotoxicity following a massive carbamazepine overdose.
- QRS complexes are broad and there is a large R’ wave in aVR.
- Beta-blocker toxicity
- Calcium-channel blocker toxicity
- Quetiapine toxicity
- Tricyclic overdose (sodium-channel blocker toxicity)
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e