Back to Basics: TCA Toxicity - EKG Findings

Tricyclic Antidepressant Mechanism of Action:

Na-channel blockade:
PR and QRS prolongation, ventricular dysrhythmias, myocardial suppression: bradycardia= bad sign, hypotension
Potassium channel inhibition:
QTc prolongation- from inhibition of potassium channels
Muscarinic (M1), Alpha-adrenergic and histaminic (H1) blockade:

tachycardia, seizures, anticholinergic syndrome, coma

EKG Findings:

R-axis deviation of QRS
Terminal R wave in aVR:
o R/S ratio >0.7
S wave in I and aVL
QRS widening/Intraventricular conduction delay:
o>100 ms associated w/ seizures
o>160 ms associated w/ cardiac dysrhythmias (VT, VF)
Sinus tachycardia
PR prolongation/AV-block (p-waves often buried) 
Right BBB
Brugada Pattern



1) Harrigan RA, Brady WJ. ECG abnormalities in tricyclic antidepressant ingestion. The American Journal of Emergency Medicine 1999; 17:387-393.


2) Scott Weingart. Podcast 98 – Cyclic (Tricyclic) Antidepressant Overdose. EMCrit Blog. Published on May 14, 2013. Accessed on May 4th 2017. Available at [ ].


3) Welsh L, et al. Section IX. environmental complains: tricyclic antidepressant toxicity. EM Fundamentals: The Essential Handbook for Emergency Medicine Residents 2016: 154-155.