How do I distinguish metabolic from toxic causes of wide-complex PEA?

Summary

Distinguishing metabolic causes (e.g., hyperkalemia) from drug-induced, clinically significant concentration causes (such as sodium channel blocker toxicity) in wide‐complex PEA relies on context, history, ECG nuances, and laboratory data. In metabolic disturbances like hyperkalemia, you often see a history of renal dysfunction or acidosis with associated ECG findings (peaked T waves progressing to widening) and lab confirmation, whereas in sodium channel blocker toxicity you may have a history suggestive of overdose, markedly prolonged QRS duration sometimes with a rightward axis, and a pattern that improves with sodium bicarbonate administration ^1 ^2.

At-a-glance

Feature	Metabolic (e.g. Hyperkalemia)	Drug Toxicity (Sodium Channel Blocker Overdose)
Clinical History	Often patients with renal failure, acidosis, or known electrolyte disturbances	History of ingestion/overdose or exposure to sodium channel blockers
ECG Characteristics	Gradual QRS widening with preceding peaked T waves; may show other hyperkalemic features	Markedly widened QRS with potential rightward axis deviation; sometimes very pronounced widening
Laboratory Evaluation	Elevated serum potassium corroborates the diagnosis	Drug levels (if available) and supportive toxicology consistent with overdose
Treatment Approach	Calcium administration (e.g., calcium gluconate), insulin-dextrose, and measures to shift potassium intracellularly	Sodium bicarbonate is central for reversing sodium channel blockade; supportive care tailored to toxin
Contextual Clues	Occur in a metabolic crisis scenario	Toxicological exposure context with corresponding clinical findings

References

LI
Pulseless Electrical Activity from Life in the Fast Lane
EMD
R.E.B.E.L. EM – Beyond ACLS: A New Pulseless Electrical Activity Algorithm from emDocs
WIK
Wide-complex tachycardia from WikEM
EMC
The Case of the Indiscriminate Waveform from EMCrit
EMO
Beyond the guidelines: an approach to cardiac arrest in the Emergency Department from EMOttawa

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