What Type of Toxicity?

What type of toxicity is associated with the attached EKG?  What would be the management?  


TCA Overdose (Sodium Channel Blockade) - Notice the terminal "tall" R wave in aVR, suggestive for sodium channel blockade which can be caused by TCA overdose.

TCAs cause a multitude of pharmacological effects that result in their toxic profile.  The most important life-threatening effect is cardiotoxicity from cardiac sodium channel blockade.  Sodium channel blockade initially manifests itself as QRS prolongation and terminal 40 milliseconds right axis deviation (terminal R wave in lead aVR and S wave in lead I), but ultimately may cause ventricular dysrhythmias and death.

Patients with a QRS duration greater than 100ms are at risk for seizures and ventricular dysrhythmias.  QRS prolongation should prompt immediate intravenous sodium bicarbonate administration. 

Given that patients may exhibit agitation and/or experience seizures, these symptoms can be treated with benzos; patients require close observation and consideration for early airway protection should be given.

CONTRAINDICATED: Physostigmine - Case Reports of bradycardia --> asystole.

Similar EKG changes can also be seen with other sodium channel blockers:

  • Tricyclic antidepressants (= most common)
  • Type Ia antiarrhythmics (quinidine, procainamide)
  • Type Ic antiarrhythmics (flecainide, encainide)
  • Local anaesthetics (bupivacaine, ropivacaine)
  • Antimalarials (chloroquine, hydroxychloroquine)
  • Dextropropoxyphene
  • Propranolol
  • Carbamazepine
  • Quinine
  • Benadryl
  • Cocaine