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ECG Disease Patterns

ECG: Sodium Channel Blockade

February 15th, 2021


A wide variety of medications achieve a therapeutic effect by blocking sodium channels. Toxicity of these medications can produce characteristic ECG findings.
Sodium channel blockers prevent influx of sodium into cardiac myocytes during phase 0 of the action potential, resulting in widening of the QRS complex.
  • ECG Findings in Sodium Channel Blocker Toxicity

  • QRS widening >100ms
  • Ventricular arrhythmias - ventricular tachycardia, ventricular fibrillation
  • Common Sodium Channel Blockers

  • Class Ia/Ic antiarrhythmics - quinidine, procainamide, flecainide
  • Tricyclic antidepressants - amitryptiline, nortriptyline
  • Local anaesthetics - bupivacaine, lidocaine, ropivacaine
  • Hydroxychloroquine
  • Carbamazepine
  • Propranolol
  • Quinine
  • Cocaine
Each of the classes of medications may be associated with other effects, for example due to concomitant sympathomimetic or anticholinergic actions of the drugs.
Tricyclic antidepressants tend to also cause sinus tachycardia and right axis deviation.
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