Back to Basics: TCA Toxicity - EKG Findings
Mon, 05/15/2017 - 5:00am
Tricyclic Antidepressant Mechanism of Action:
–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
•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)
•PR prolongation/AV-block (p-waves often buried)
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 [https://emcrit.org/podcasts/tricyclic-antidepressant-overdose/ ].
3) Welsh L, et al. Section IX. environmental complains: tricyclic antidepressant toxicity. EM Fundamentals: The Essential Handbook for Emergency Medicine Residents 2016: 154-155.