UMEM Educational Pearls

Title: Tricyclic Antidepressant Cardiotoxicity

Posted: 8/10/2014 by Semhar Tewelde, MD
Click here to contact Semhar Tewelde, MD

- Toxic effects of tricyclic antidepressants (TCA) are result of the following 4 pharmacologic properties:

1. Inhibition of norepinephrine & serotonin reuptake --> resultant seizure

2. Anticholinergic activity --> resultant altered mental status, tachycardia, mydriasis, ileus

3. Direct alpha-adrenergic blockade --> resultant hypotension

4. Cardiac myocyte sodium channel blockade --> resultant widened QRS

- A QRS interval greater than 100 milliseconds has ~30% chance of developing seizures and ~15% chance of developing a life-threatening cardiac arrhythmia.

- A QRS interval greater than 160 milliseconds increases the chance of ventricular arrhythmias to greater than 50%.

- Clinical pearl: A very wide complex ventricular rhythm, concomitant hypotension and/or seizure disorder is suspicious for toxic ingestion and standard ACLS algorithm will not suffice, treatment must address the underlying culprit (i.e. TCA --> Tx. fluids, vasopressors, sodium bicarbonate, and intravenous lipid emulsion).

References

Kerr GW, McGuffie AC, Wilkie S. Tricyclic antidepressant overdose: a review. Emerg Med J. Jul 2001;18(4):236-41.