In many toxicologic emergencies, the ECG is not just diagnostic. It is a resuscitation monitor.
This is especially true in sodium channel blocker toxicity.
Fast sodium channels are essential for phase 0 depolarization in cardiac myocytes. When these channels are blocked, ventricular depolarization slows.
On the ECG, this appears as QRS widening. The wider the QRS, the more unstable the conduction system becomes.
Severe sodium channel blockade can lead to ventricular dysrhythmias, hypotension, seizures, and cardiac arrest.