Carbamazepine Cardiotoxicity

Massive carbamazepine overdose (> 50mg/kg) is associated with cardiotoxicity due to fast sodium channel blockade. ECG changes are not usually as dramatic as those seen in TCA overdose.

ECG features of Carbamazepine Cardiotoxicity

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

• Beta-blocker toxicity
• Calcium-channel blocker toxicity
• Quetiapine toxicity
• Tricyclic overdose (sodium-channel blocker toxicity)

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Yellow Belt online course: Become an ECG expert. Medmastery
• Wiesbauer F, Kühn P. ECG Blue Belt online course: Learn to diagnose any rhythm problem. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Hampton J. The ECG Made Practical 7e, 2019
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

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