Carbamazepine Cardiotoxicity

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.

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