Antiarrhythmic Agent Overdose

KEY FEATURES

• Class Ia antiarrhythmic agents

  • Quinidine

  • Disopyramide

  • Procainamide

• Class Ic antiarrhythmic agents

  • Flecainide

  • Propafenone

• These drugs have membrane-depressant effects on the sodium-dependent channel responsible for cardiac cell depolarization

CLINICAL FINDINGS

• Arrhythmias

• Syncope

• Hypotension

DIAGNOSIS

• Blood levels of quinidine and procainamide (and active metabolite NAPA) are generally available from hospital laboratory

• ECG monitoring for QRS and QT interval prolongation

  • Widening of the QRS complex (> 100–120 ms)

  • With type Ia drugs, a lengthened QT interval and atypical or polymorphous ventricular tachycardia (torsades de pointes) may occur

TREATMENT

• Activated charcoal

  • Administer 60–100 g orally or via gastric tube, mixed in aqueous slurry for ingestions within 1–2 hours

  • Do not use for comatose or convulsing patients unless they are endotracheally intubated

  • Repeated doses may be given to ensure gastrointestinal absorption or to enhance elimination of some drugs

• Consider gastric lavage for recent (1 hour) large ingestions

• Assist ventilation as needed

• Perform continuous cardiac monitoring

• Consider whole bowel irrigation for ingestion of sustained-release formulations

• Treat cardiotoxicity (hypotension, QRS interval widening) with intravenous boluses of sodium bicarbonate, 50–100 mEq

• Torsades de pointes ventricular tachycardia may be treated with intravenous magnesium or overdrive pacing