QRS widening / NaV1.5

Interaction at a glance

• Fast cardiac Na+ channel block slows conduction

Mechanism

• Fast cardiac Na+ channel block slows conduction
• QRS widens as ventricular depolarization slows

Clinical consequence

• Marked widening predicts severe toxicity
• This is distinct from hERG/QTc prolongation

Management

• TCA overdose is the classic example

Self-check

• What does marked QRS widening suggest?
  Severe toxicity.
• What classic overdose causes NaV1.5-mediated QRS widening?
  TCA overdose.

Drugs in this interaction (63)

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