What is the first line antiarrhythmic (arrhythmia) drug?

First-Line Antiarrhythmic Drug Selection

The first-line antiarrhythmic drug depends critically on the specific arrhythmia type and underlying cardiac pathology, but adenosine is the first-line agent for acute supraventricular tachycardia, while beta-blockers represent the safest and most evidence-based first-line choice for most chronic arrhythmia management, particularly in patients with structural heart disease. 1, 2

Acute Supraventricular Tachycardia (SVT)

For acute SVT termination, adenosine is the definitive first-line drug after vagal maneuvers fail. 1, 2

• Dosing: 6 mg rapid IV bolus with saline flush; if ineffective after 1-2 minutes, give 12 mg (may repeat once). 2
• Adenosine works specifically for AV nodal re-entrant tachyarrhythmias with a very short half-life, making it unlikely to reach fetal circulation in pregnancy. 1
• Critical caveat: Must be administered in a monitored environment as it causes transient complete heart block; contraindicated in asthmatics due to bronchospasm risk. 2

Second-line options if adenosine fails include:

• Beta-blockers (metoprolol or propranolol IV) are reasonable alternatives, particularly in pregnancy where they have extensive safety data. 1
• Verapamil (5-10 mg IV over 60 seconds) may be used but carries higher hypotension risk than adenosine and is absolutely contraindicated if beta-blockers have been given or in Wolff-Parkinson-White syndrome. 2

Ventricular Tachycardia (VT)

For stable VT with pulse, lidocaine (lignocaine) is the first-choice antiarrhythmic. 2

• Dosing: 50 mg IV over 2 minutes, repeated every 5 minutes to total 200 mg, followed by maintenance infusion at 2 mg/min. 2
• Alternative dosing: 1-3 mg/kg IV bolus (not exceeding 100 mg), then 2-4 mg/min infusion. 2

For refractory or recurrent VT (VT storm):

• Amiodarone becomes first-line: 150 mg IV over 10 minutes, then 1.0 mg/min for 6 hours, then 0.5 mg/min maintenance. 2, 3
• Beta-blockers IV are the single most effective therapy for polymorphic VT storm. 3

Critical distinction: For unstable VT with pulse, immediate synchronized cardioversion (100J, 200J, 360J) takes precedence over pharmacotherapy. 2

Atrial Fibrillation (AF) - Rhythm Control

Safety considerations dictate first-line selection more than efficacy, as most antiarrhythmics have similar effectiveness. 1

In Structurally Normal Hearts (No CAD, No Heart Failure, No LVH):

Flecainide or propafenone are first-line agents for maintaining sinus rhythm. 1, 4

• These class IC agents have the lowest proarrhythmic risk and organ toxicity in normal hearts. 5
• Absolute contraindication: Never use in ischemic heart disease or heart failure due to life-threatening ventricular arrhythmia risk. 1
• Require pre-treatment with beta-blocker, verapamil, or diltiazem to prevent high ventricular rates from AF converting to 1:1 atrial flutter. 1

In Coronary Artery Disease:

Sotalol is preferred as first-line due to substantial beta-blocking activity and less long-term toxicity than amiodarone. 1

• Beta-blockers alone may be considered first but lack convincing efficacy data for maintaining sinus rhythm post-cardioversion. 1
• Amiodarone is reserved for second-line or when heart failure coexists. 1

In Heart Failure:

Amiodarone or dofetilide are the only safe first-line options. 1, 4

• These are the only agents proven safe in randomized trials of heart failure patients. 1
• Dronedarone is absolutely contraindicated in recently decompensated heart failure due to increased mortality. 1

In Hypertensive Heart Disease with LVH:

Propafenone or flecainide are first-line if no marked LVH and no CAD. 1

• Avoid QT-prolonging agents (sotalol, dofetilide) due to increased torsades de pointes risk with LVH. 1
• Amiodarone becomes first-line when marked LVH is present despite QT prolongation, as it carries very low ventricular proarrhythmia risk. 1

Chronic Prophylaxis and Mortality Reduction

Beta-blockers are the only antiarrhythmic class definitively proven to reduce sudden arrhythmic death and overall mortality. 4, 6

• This benefit is most pronounced post-myocardial infarction and in heart failure patients. 4, 7
• Beta-blockers should be considered first-line for maintaining sinus rhythm in AF patients with MI, heart failure, or hypertension. 7
• Metoprolol CR/XL has specific evidence for maintaining sinus rhythm after AF cardioversion. 7

Critical Safety Principles

The overarching principle: Safety trumps efficacy in antiarrhythmic selection. 1

• Most antiarrhythmic drugs have similar modest efficacy (approximately doubling sinus rhythm maintenance vs. no therapy). 1
• Quinidine and disopyramide are associated with increased all-cause mortality and should be avoided as first-line agents. 1
• Class I drugs (except in structurally normal hearts) and class III drugs carry significant proarrhythmic risk that often outweighs benefits. 4, 5
• Amiodarone, while highly effective, causes frequent extracardiac toxicity (thyroid, pulmonary, hepatic) and is relegated to second-line therapy except in heart failure. 1