What are the antiarrhythmic drugs used to treat ventricular tachycardia?

Treatment of Ventricular Tachycardia with Antiarrhythmic Drugs

For hemodynamically stable VT, intravenous amiodarone (150 mg over 10 minutes, followed by 1.0 mg/min for 6 hours, then 0.5 mg/min maintenance) combined with beta-blockers is the preferred first-line therapy, while lidocaine serves as an alternative particularly when VT is ischemia-related. 1, 2

Hemodynamic Assessment Determines Treatment Strategy

The critical first step is determining pulse presence and hemodynamic stability—specifically checking for hypotension (systolic BP ≤90 mmHg), chest pain, heart failure, or extreme heart rate. 3, 4 This assessment dictates whether electrical or pharmacological intervention takes priority.

For Hemodynamically Unstable VT (with pulse but hypotensive):

• Immediate synchronized DC cardioversion is mandatory (100J, 200J, 360J escalation) with sedation if the patient is conscious. 1, 3, 4
• Pharmacological therapy is secondary in this scenario. 3

For Hemodynamically Stable VT:

Proceed with antiarrhythmic drug therapy as outlined below.

First-Line Antiarrhythmic Therapy

Amiodarone (Preferred Agent)

Amiodarone is the preferred antiarrhythmic for severe, symptomatic, sustained VT, particularly in patients with heart failure or structural heart disease. 5, 1

Dosing regimen:

• Loading dose: 150 mg IV over 10 minutes 1, 2
• Maintenance infusion: 1.0 mg/min for 6 hours 1, 2
• Continued maintenance: 0.5 mg/min thereafter 1, 2
• For breakthrough VT episodes: Repeat the 150 mg loading dose 1, 2

The FDA approves amiodarone for initiation of treatment and prophylaxis of frequently recurring VF and hemodynamically unstable VT in patients refractory to other therapy. 2 Most patients require 48-96 hours of IV therapy before transitioning to oral amiodarone. 2

Combination with beta-blockers: The European Society of Cardiology specifically recommends combining IV amiodarone with beta-blockers for VT storm, as beta-blockers represent the single most effective therapy for polymorphic VT storm. 1

Lidocaine (Alternative First-Line Agent)

Lidocaine is recommended as an alternative or adjunct to amiodarone, particularly when VT is thought to be ischemia-related. 1, 3, 4

Dosing regimen:

• Initial bolus: 1.0-1.5 mg/kg IV (typically 50-100 mg) 1, 3
• Supplemental boluses: 0.5-0.75 mg/kg every 5-10 minutes to maximum total loading dose of 3 mg/kg (or 200 mg total) 1, 3
• Maintenance infusion: 2-4 mg/min 1, 3, 4

Critical dosing adjustments:

• Reduce infusion rates in elderly patients, those with heart failure, or hepatic dysfunction to avoid toxicity. 1
• The half-life increases over time, so reduce infusion after 24-48 hours. 3
• Monitor for CNS toxicity (drowsiness, perioral numbness, confusion, seizures). 3

Second-Line Antiarrhythmic Options

Procainamide

For VT refractory to amiodarone or lidocaine, procainamide is a reasonable alternative. 1, 4

Dosing regimen:

• Loading infusion: 20-30 mg/min up to 12-17 mg/kg 1
• Maintenance infusion: 1-4 mg/min 1
• Dose adjustment: Reduce infusion rates in patients with renal dysfunction. 1

Dofetilide

Dofetilide is mentioned as an alternative option for patients with heart failure and ventricular arrhythmias, though it requires careful monitoring. 5

Special Situations

Torsades de Pointes

Administer magnesium 8 mmol (2 grams) IV for torsades de pointes, especially if hypomagnesemia is suspected. 1, 3 Follow with maintenance infusion of 2.5 mmol/hour. 3

VT Storm (Recurrent/Incessant VT)

• Aggressive beta-blockade is the single most effective therapy for polymorphic VT storm. 1
• Combine IV amiodarone with beta-blockers as first-line. 1
• Consider overdrive pacing, general anesthesia, or spinal cord modulation for refractory cases. 1
• Address underlying causes: treat heart failure aggressively, manage myocardial ischemia, and consider coronary revascularization if acute ischemia is evident. 1

Drug-Refractory Polymorphic VT

Implement aggressive measures to reduce myocardial ischemia: maximize beta-blockade, consider intra-aortic balloon pump, and evaluate for emergency revascularization (PTCA/CABG). 1

Critical Contraindications and Precautions

Avoid calcium channel blockers (verapamil, diltiazem) in VT patients, especially those with myocardial dysfunction, as they can precipitate VT/VF or profound hypotension. 3

Amiodarone is contraindicated in:

• Cardiogenic shock 2
• Marked sinus bradycardia 2
• Second- or third-degree AV block without functioning pacemaker 2
• Known hypersensitivity to amiodarone or iodine 2

Monitor closely for:

• Hypotension (slow infusion rate, add vasopressors or volume expansion as needed) 2
• Bradycardia and AV block (slow or discontinue infusion) 2
• Myocardial depression with all antiarrhythmics, especially in already compromised patients 3, 4

What NOT to Do

The routine use of antiarrhythmic agents for asymptomatic premature ventricular complexes or non-sustained VT is not justified. 5 Reserve antiarrhythmic therapy for severe, symptomatic, sustained VT. 5

Class IC agents (flecainide, propafenone) and class IA agents (quinidine, procainamide, disopyramide) can theoretically accelerate tachycardia in some anatomically determined circuits, making individual monitoring essential. 6

Practical Administration Tips

• Always administer IV drugs with a 20 mL saline bolus to aid delivery to central circulation. 3, 4
• When no venous access is available, drugs (particularly epinephrine) may be delivered via endotracheal route in double or triple doses. 3
• Correct electrolyte abnormalities (potassium, magnesium) before and during antiarrhythmic therapy. 5, 3