How to use antiarrhythmic drug what are the indication and contraindications
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Here is a comprehensive guide to antiarrhythmic drugs (AADs), organized by the Vaughan Williams Classification.
Antiarrhythmic Drugs (AADs)
Overview
AAD use is based on careful assessment of risks and potential benefit for each individual patient. Efficacy and side effects are not fully predictable and must be assessed by individual therapeutic trial. Importantly, most AADs have multiple effects — they act on more than one channel or receptor simultaneously. (Harrison's, p. 7068)
⚠️ Proarrhythmia Risk: A major concern with ALL antiarrhythmic drugs is that they can increase the frequency of existing arrhythmias or cause new ones. Aggravation of bradyarrhythmias is also common.
Vaughan Williams Classification (Harrison's, p. 6940)
| Class | Target | Primary Action | Key Drugs |
|---|---|---|---|
| I | Na⁺ channels | Membrane stabilization | Ia: Quinidine, Procainamide, Disopyramide |
| Ib: Lidocaine, Mexiletine | |||
| Ic: Flecainide, Propafenone | |||
| II | β-adrenergic receptors | Sympathetic blockade | Metoprolol, Atenolol, Esmolol, Propranolol |
| III | K⁺ channels | Prolongs repolarization | Amiodarone, Sotalol, Dofetilide, Ibutilide |
| IV | Ca²⁺ channels (L-type) | Slows AV node conduction | Verapamil, Diltiazem |
Class-by-Class: Indications & Contraindications
Class I — Sodium Channel Blockers
Class Ia (Moderate Na⁺ block + K⁺ block → prolongs QRS & QT)
| Drug | Indications | Contraindications |
|---|---|---|
| Quinidine | AF/AFL (rhythm control), VT, WPW | Heart failure, QT prolongation, complete AV block, digoxin toxicity |
| Procainamide | AF/VT (acute IV), WPW with AF | SLE-like syndrome risk (long-term), heart failure, QT prolongation, torsades history |
| Disopyramide | AF/VT, vagally-mediated AF (negative inotropy used in HCM) | Uncompensated HF (strong negative inotrope), urinary retention, glaucoma, prolonged QT |
Class Ib (Weak Na⁺ block → shortens action potential; mainly in ventricles)
| Drug | Indications | Contraindications |
|---|---|---|
| Lidocaine | Acute ventricular arrhythmias (VT/VF), post-MI VT (IV only) | Sinoatrial disorder, AV block (without pacemaker), severe hepatic failure |
| Mexiletine | Chronic ventricular arrhythmias (oral), adjunct in long QT syndrome (LQT3) | Cardiogenic shock, 2nd/3rd degree AV block |
Class Ic (Strong Na⁺ block → markedly slows conduction, widens QRS)
| Drug | Indications | Contraindications |
|---|---|---|
| Flecainide | Paroxysmal AF/AFL (rhythm control), SVT, AVNRT | Structural heart disease (post-MI, HF, LV dysfunction) — risk of proarrhythmia/death (CAST trial) |
| Propafenone | Paroxysmal AF, SVT, WPW | Structural heart disease, severe COPD/asthma (has mild β-blocking activity), decompensated HF |
Class II — Beta-Blockers
Mechanism: Reduce automaticity of the SA node, slow AV nodal conduction, decrease sympathetic drive.
Indications:
- Rate control in atrial fibrillation/flutter
- SVT (AVNRT, AVRT)
- Post-MI arrhythmia prophylaxis
- Catecholaminergic polymorphic VT (CPVT) — first-line
- Long QT syndrome (LQT1, LQT2)
- Heart failure with reduced EF (carvedilol, metoprolol succinate)
- Thyrotoxicosis-related arrhythmias
Contraindications:
- Severe bradycardia or sick sinus syndrome (without pacemaker)
- High-degree AV block (2nd or 3rd degree, without pacemaker)
- Decompensated heart failure (acute phase)
- Severe reactive airway disease (non-cardioselective agents)
- Cocaine-induced arrhythmias (risk of unopposed alpha stimulation)
Class III — Potassium Channel Blockers
Mechanism: Prolong repolarization (action potential duration), prolong QT interval.
| Drug | Indications | Contraindications |
|---|---|---|
| Amiodarone | AF/AFL (rhythm control), VT/VF (first-line in cardiac arrest), HF with arrhythmia | Thyroid disease (relative), pulmonary toxicity risk, iodine allergy; bradycardia, QT prolongation, liver disease |
| Sotalol | AF rhythm control, VT suppression | Renal failure (dose-adjusted), bradycardia, QTc >500 ms, hypokalemia, asthma (has β-blocking activity) |
| Dofetilide | AF/AFL (rhythm control) — especially with HF | Renal impairment, baseline QTc >440 ms, drug interactions (multiple CYP3A4 inhibitors) |
| Ibutilide | Acute conversion of AF/AFL (IV only) | Prolonged baseline QT, hypokalemia, hypomagnesemia, prior torsades de pointes |
Class IV — Calcium Channel Blockers (Non-Dihydropyridine)
Mechanism: Block L-type Ca²⁺ channels → slow SA/AV nodal conduction.
| Drug | Indications | Contraindications |
|---|---|---|
| Verapamil | Rate control in AF/AFL, termination of AVNRT/AVRT, idiopathic left VT (Belhassen VT) | Pre-excitation (WPW) with AF (can accelerate accessory pathway conduction → VF), HF with reduced EF, cardiogenic shock, AV block, concurrent beta-blocker use (IV) |
| Diltiazem | Rate control in AF/AFL, AVNRT | Same as verapamil; less negative inotropy |
Other Agents (Outside Vaughan Williams)
| Drug | Indications | Contraindications |
|---|---|---|
| Adenosine | First-line for acute termination of SVT (AVNRT/AVRT) | 2nd/3rd degree AV block, sick sinus syndrome, severe asthma; use caution in WPW |
| Digoxin | Rate control in AF (especially with HF, sedentary patients) | WPW, hypertrophic obstructive cardiomyopathy, AV block, renal failure (accumulation) |
| Atropine | Symptomatic bradycardia, AV block (acute) | Narrow-angle glaucoma, urinary obstruction, tachycardia |
| Magnesium sulfate | Torsades de pointes, digoxin toxicity, refractory VF | Renal failure, hypermagnesemia |
General Principles of Use
- Match drug to arrhythmia mechanism — atrial vs. ventricular, re-entry vs. automaticity.
- Assess structural heart disease first — Class Ic agents are contraindicated in structural/ischemic heart disease.
- Monitor QT interval — Class Ia, Ic, and III agents can all prolong QT → risk of torsades de pointes.
- Electrolyte correction — hypokalemia and hypomagnesemia potentiate drug-induced arrhythmias.
- Drug interactions — amiodarone raises levels of warfarin, digoxin, and many others.
- Renal/hepatic dosing — sotalol and dofetilide require renal adjustment.
- Proarrhythmia surveillance — in-hospital initiation is often required (especially dofetilide, sotalol, IV ibutilide).
Sources: Harrison's Principles of Internal Medicine, 21st Edition, pp. 6940 & 7068
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