TCA Toxicity and Bicarbonate: Mechanism

Sodium bicarbonate has become the mainstay treatment for arrhythmias caused by TCA toxicity.

The cardiotoxic effects of TCA work via blockade of the rapid sodium channels (see below- stage 0).

There will be a characteristic prolongation of the QRS. Potentiating hemodynamic instability.

HOW DOES BICARBONATE HELP?

The benefit of sodium bicarbonate (NaHCO3) is primarily related the sodium component. Increasing the extracellular sodium concentration results in an increase of the electrochemical gradient across cardiac cell membranes. This in effect works to attenuate the TCA-induced blockade of rapid sodium channels.

Also the alkalization of the blood from bicarbonate shifts TCA towards its non-ionized form, reducing its ability to bind sodium channels.

REFERENCES

1. Sasyniuk BI, Jhamandas V. Mechanism of reversal of toxic effects of amitriptyline on cardiac Purkinje fibers by sodium bicarbonate. J Pharmacol Exp Ther. 1984;231(2):387.
2. Bruccoleri RE, Burns MM. A Literature Review of the Use of Sodium Bicarbonate for the Treatment of QRS Widening. J Med Toxicol. 2016 Mar;12(1):121-9.