Antiarrhythmics

Antiarrhythmics are medicines used to treat abnormal heart rhythms by altering the electrical activity of the heart. They can decrease automaticity, slow conduction, or prolong repolarization, thereby suppressing abnormal impulses and restoring or maintaining a regular rhythm. They are used for atrial and ventricular arrhythmias, including atrial fibrillation, atrial flutter, ventricular tachycardia, and supraventricular tachycardia.

The major clinical framework for these drugs is the Vaughan Williams classification, which groups agents by mechanism. Class I are sodium channel blockers that slow depolarization; they are subdivided into IA (quinidine, procainamide), IB (lidocaine, mexiletine), and IC (flecainide, propafenone). Class II comprises beta-adrenergic blockers (metoprolol, atenolol, propranolol, esmolol) that reduce automaticity and AV nodal conduction. Class III agents prolong repolarization by blocking potassium channels (amiodarone, sotalol, dofetilide, ibutilide). Class IV agents are non-dihydropyridine calcium channel blockers (diltiazem, verapamil) that slow AV nodal conduction. Amiodarone is frequently used but has multiple mechanisms and effects beyond a single class.

In addition to these classes, other agents include adenosine for acute termination of AV-node–dependent SVT; digoxin for rate control in atrial fibrillation and heart failure; and magnesium sulfate for torsades de pointes or hypomagnesemia-related arrhythmias. Antiarrhythmics may be used for rhythm control or rate control and can be given orally or intravenously.

Safety and monitoring are essential. Proarrhythmia risk (including torsades de pointes), hypotension, bradycardia, and conduction block can occur. Therapy is individualized, with attention to underlying heart disease, electrolyte balance, renal and hepatic function, and potential drug interactions.