Antiarrhythmics — Vaughan-Williams Classification

Also known as Antiarrhythmics · Vaughan-Williams · Class I sodium channel blockers · Class II beta-blockers · Class III potassium channel blockers · Class IV calcium channel blockers · Amiodarone · Lidocaine · Procainamide · Flecainide · Adenosine · Digoxin · Sicilian Gambit

Antiarrhythmics — the Vaughan-Williams classification: Class I (the sodium channel blockers — Ia quinidine/procainamide [prolong AP + QT], Ib lidocaine/phenytoin [shorten AP, ischaemic-tissue selectivity], Ic flecainide/propafenone [markedly slow conduction, AVOID in structural heart disease — CAST]); Class II (the beta-blockers — metoprolol/esmolol/bisoprolol — slow AV node, reduce sympathetic); Class III (the potassium channel blockers — amiodarone [multichannel, half-life ~60 days, multi-organ toxicity], sotalol, ibutilide, dofetilide, dronedarone); Class IV (the calcium channel blockers — verapamil/diltiazem, non-dihydropyridine only); and the others (digoxin, adenosine, magnesium). Includes the Singh-Vaughan Williams mechanism, the Sicilian Gambit, each drug's indication/dose/adverse effects/contraindications/QT risk, and a full amiodarone toxicity deep dive (pulmonary, thyroid, hepatic, skin).

high35 referencesUpdated 19 Aug 202618 min readSource-verified · Oct 2026

Checked against its sources on 1 Oct 2026

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8 MCQs

Meet the patient

A 68-year-old man on day 4 of ICU for pneumonia has just gone into fast atrial fibrillation — ventricular rate 148, irregularly irregular, BP 88/54 on a low-dose noradrenaline, K+ 3.2, Mg2+ 0.55. He is borderline shocked, sweaty, mildly confused. The question lands before the rhythm strip finishes printing: do you shock him, drug him, or both — and which drug? ^[1]

The three questions that decide the answer are the same three that decide every ICU arrhythmia: is the patient stable? (shock, ischaemic pain, pulmonary oedema, coma → synchronised DC cardioversion), what is the rhythm? (atrial vs ventricular, narrow vs broad, regular vs irregular), and is there structural heart disease? (bars flecainide and the other Class Ic agents). Hold those three questions and the rest of the page slots into place.^[1]

References35Show

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