A four-class system organizing antiarrhythmics by mechanism: Class I (sodium channel blockers, e.g. lidocaine), Class II (beta blockers, e.g. esmolol), Class III (potassium channel blockers, e.g. amiodarone), Class IV (calcium channel blockers, e.g. diltiazem) — with Class IV agents contraindicated in pre-excited AF.
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