Arrhythmias are abnormal heart rhythms caused by disturbances in impulse formation or conduction. Management includes antiarrhythmic drugs (AADs), electrical interventions (cardioversion, pacemakers), and catheter ablation. Proper selection of antiarrhythmic therapy depends on the type of arrhythmia, hemodynamic stability, and underlying heart disease.
2. Classification of Antiarrhythmic Drugs (Vaughan-Williams Classification)
| Class | Mechanism of Action | Examples | Indications |
|---|---|---|---|
| Class I (Sodium Channel Blockers) | Slows depolarization (Phase 0) | Quinidine, Procainamide, Lidocaine, Flecainide | SVT, VT, AF (not first-line) |
| Class II (Beta-Blockers) | Decreases SA & AV node activity | Metoprolol, Esmolol, Propranolol | AF, SVT, rate control |
| Class III (Potassium Channel Blockers) | Prolongs repolarization (Phase 3) | Amiodarone, Sotalol, Dofetilide | AF, VT, VF prevention |
| Class IV (Calcium Channel Blockers) | Blocks AV node conduction | Verapamil, Diltiazem | SVT, rate control in AF |
| Class V (Others) | Mixed actions | Digoxin, Adenosine, Magnesium | AF rate control (Digoxin), SVT (Adenosine), Torsades (Magnesium) |
🚨 Amiodarone has broad-spectrum activity but high toxicity.
🚨 Class I and III agents are proarrhythmic—use with caution in structural heart disease.
3. Common Arrhythmias and Their Management
(A) Atrial Fibrillation (AF)
🔹 Irregularly irregular rhythm, no P waves
🔹 Management goals: Rate control, rhythm control, stroke prevention
| Stable AF | Unstable AF (Hypotension, Shock, HF) |
|---|---|
| Rate Control (Beta-blockers, CCBs, Digoxin) | Immediate DC Cardioversion |
| Rhythm Control (Amiodarone, Flecainide, Sotalol) | Consider IV Amiodarone |
| Anticoagulation (CHA₂DS₂-VASc ≥2) | Anticoagulation post-cardioversion |
(B) Supraventricular Tachycardia (SVT)
🔹 Narrow QRS tachycardia, regular rhythm
🔹 Causes: AV nodal re-entry, WPW, atrial tachycardia
| Stable SVT | Unstable SVT (Hypotension, Shock, Ischemia) |
|---|---|
| Vagal Maneuvers (Carotid massage, Valsalva) | Immediate Synchronized DC Cardioversion |
| Adenosine (6mg → 12mg IV push) | Beta-blockers or Calcium Channel Blockers if needed |
| Beta-blockers, Verapamil (Maintenance therapy) | Consider Ablation for Recurrent SVT |
(C) Ventricular Tachycardia (VT)
🔹 Wide QRS tachycardia
🔹 Causes: Ischemia, electrolyte imbalance, structural heart disease
| Stable VT | Unstable VT (Hypotension, Shock, Pulmonary Edema, Chest Pain) |
|---|---|
| Amiodarone IV (150mg over 10 min) | Immediate Synchronized DC Cardioversion |
| Lidocaine (if Amiodarone contraindicated) | Magnesium (if Torsades de Pointes) |
| Consider ICD for Secondary Prevention | Long-term: Beta-blockers, Amiodarone |
🚨 If VT is polymorphic (Torsades de Pointes), give Magnesium Sulfate!
(D) Ventricular Fibrillation (VF) / Pulseless VT
🚨 Cardiac arrest! Immediate CPR and defibrillation required
| Immediate Actions | If VF/VT Persists |
|---|---|
| Defibrillation (200J biphasic or 360J monophasic) | Epinephrine 1mg IV every 3-5 mins |
| High-Quality CPR | Amiodarone (300mg IV, then 150mg) |
| Shockable Rhythm? → Repeat Defibrillation | Consider Lidocaine if refractory |
(E) Bradyarrhythmias (Sinus Bradycardia, AV Block)
🔹 Causes: Ischemia, drug toxicity (beta-blockers, digoxin), sick sinus syndrome
| Stable Bradycardia | Unstable (Hypotension, Syncope, Shock) |
|---|---|
| Monitor, stop offending drugs | Atropine 0.5mg IV (repeat every 3-5 min, max 3mg) |
| Pacemaker if persistent symptomatic bradycardia | Transcutaneous pacing if Atropine ineffective |
🚨 Third-degree (complete) heart block needs a pacemaker.
4. Non-Pharmacological Interventions
| Procedure | Indication |
|---|---|
| Electrical Cardioversion | Unstable AF, SVT, VT |
| Ablation Therapy | Recurrent SVT, WPW, some VT cases |
| Implantable Cardioverter-Defibrillator (ICD) | Secondary prevention in VT/VF survivors |
| Pacemaker (PPM/CRT) | Symptomatic bradycardia, AV block, HF with LBBB |
5. Summary Table: Antiarrhythmic Drug Selection by Arrhythmia Type
| Arrhythmia | First-Line Treatment | Alternative Therapy |
|---|---|---|
| Atrial Fibrillation (Rate Control) | Beta-blockers, Verapamil/Diltiazem | Digoxin (in HF patients) |
| Atrial Fibrillation (Rhythm Control) | Amiodarone, Flecainide, Sotalol | Catheter Ablation |
| SVT (Acute Termination) | Adenosine | Beta-blockers, Verapamil |
| Ventricular Tachycardia (Stable) | Amiodarone | Lidocaine, Beta-blockers |
| Torsades de Pointes | Magnesium Sulfate | Isoproterenol, Pacing |
| Ventricular Fibrillation | CPR + Defibrillation | Epinephrine, Amiodarone |
| Bradycardia / Heart Block | Atropine | Pacemaker if persistent |
6. Key Takeaways
✅ Beta-blockers and calcium channel blockers are preferred for rate control.
✅ Amiodarone is broad-spectrum but has long-term toxicity (thyroid, lungs, liver).
✅ Adenosine is first-line for SVT but should not be used in WPW + AF.
✅ Torsades de Pointes is treated with Magnesium, NOT antiarrhythmics.
✅ ICD implantation is essential for preventing sudden cardiac death in VT/VF patients.
Further Reading
- NHS Overview of Arrhythmia Management: NHS UK
- European Society of Cardiology (ESC) Guidelines: ESC Guidelines
