What antiarrhythmic should I give a 60-year-old hemodynamically stable female with idiopathic ventricular tachycardia and frequent supraventricular tachycardia (every 1 minute 30 seconds), already receiving bisoprolol and magnesium with potassium >4 mmol/L, who is awaiting ablation next week?

Intravenous Amiodarone for Bridging to Ablation

For your hemodynamically stable 60-year-old patient with idiopathic VT and frequent SVT already on bisoprolol, intravenous amiodarone is the most appropriate antiarrhythmic to bridge her to ablation next week, given its efficacy for both ventricular and supraventricular arrhythmias and acceptable safety profile in structurally normal hearts. 1, 2

Rationale for Amiodarone Selection

Amiodarone is uniquely suited for this clinical scenario because it suppresses both ventricular tachycardia and supraventricular tachycardia through its multi-class antiarrhythmic effects. 2 Unlike class Ic agents (flecainide, propafenone) which are contraindicated in structural heart disease, or sotalol which requires careful QT monitoring, amiodarone can be used safely in idiopathic VT while simultaneously controlling the SVT episodes. 3

The 2015 ACC/AHA/HRS guidelines support intravenous amiodarone for acute rate control in supraventricular arrhythmias when beta blockers are ineffective or contraindicated (Class IIa recommendation). 3 Since your patient continues to have breakthrough SVT every 90 seconds despite bisoprolol, amiodarone represents the logical next step. 3

For ventricular tachycardia specifically, amiodarone is recommended for hemodynamically stable monomorphic VT, particularly in non-ischemic cardiomyopathy. 3, 4 The 2010 International Consensus on Resuscitation supports amiodarone for stable VT with or without heart failure. 3

Dosing Protocol

Administer the standard FDA-approved loading regimen: 1

• Loading dose: 150 mg IV over 10 minutes (diluted in 100 mL D5W) 4, 1
• Early maintenance: 1 mg/min infusion for 6 hours (360 mg total) 4, 1
• Late maintenance: 0.5 mg/min for the remaining 18 hours (540 mg total) 4, 1
• Total first 24 hours: Approximately 1000 mg 1

For breakthrough VT episodes: Give supplemental 150 mg boluses over 10 minutes, not exceeding 2.2 g total in 24 hours. 4, 1

Continue the maintenance infusion at 0.5 mg/min until ablation (up to 2-3 weeks is safe based on clinical trial data). 1

Critical Administration Requirements

Use a central venous catheter if amiodarone concentration exceeds 2 mg/mL to prevent peripheral vein phlebitis. 4, 1 Administer only in D5W (never normal saline), use an in-line filter, and employ a volumetric infusion pump—drop counters can underdose by up to 30%. 1

Monitoring Imperatives Given Concurrent Bisoprolol

This is the most important caveat: Your patient is already on bisoprolol, which creates additive AV nodal suppression with amiodarone. 4

Mandatory continuous ECG monitoring for: 4

• Heart rate (bradycardia occurs in 4.9% of patients on IV amiodarone alone) 4
• PR interval prolongation
• Development of second- or third-degree heart block (absolute contraindication to continued therapy without pacemaker) 4
• QT prolongation

If heart rate drops by ≥10 beats per minute, reduce the infusion rate immediately. 4 Hypotension occurs in 16-26% of patients, so continuous blood pressure monitoring is essential. 4

Consider reducing the bisoprolol dose by 50% when starting amiodarone to minimize the risk of excessive bradycardia, though this is not explicitly mandated in guidelines. 4 The full interaction effect peaks around 6 weeks due to amiodarone's long half-life, but acute effects can occur. 4

Why Not Other Antiarrhythmics?

Procainamide is an alternative for stable monomorphic VT but has no efficacy for SVT and requires infusion at 20-50 mg/min with frequent hypotension. 4 It would not address her SVT episodes. 3

Sotalol could theoretically treat both arrhythmias but requires careful QT monitoring and dose titration, making it impractical for acute bridging therapy. 3 It also has significant proarrhythmic risk. 3

Lidocaine is ineffective for SVT and only addresses the VT component. 3

Class Ic agents (flecainide, propafenone) are reasonable for SVT but should be avoided in VT without confirming absence of structural heart disease. 3

Expected Timeline of Effect

The antiarrhythmic effect typically appears within 20-30 minutes after the loading dose, but maximal suppression often requires 6-8 hours and at least 1 g cumulative dose. 4 This delayed onset is acceptable given her hemodynamic stability and the one-week timeline to ablation. 4

Common Pitfalls to Avoid

• Do not use evacuated glass containers for mixing—they cause precipitation. Use glass or polyolefin bottles only. 1
• Do not exceed 30 mg/min initial infusion rate—faster rates have caused hepatocellular necrosis and acute renal failure. 1
• Do not combine with other QT-prolonging antiarrhythmics (Class IA or III agents) due to additive proarrhythmic risk. 5
• Verify potassium remains >4 mmol/L throughout therapy—hypokalemia increases proarrhythmic risk despite your patient's current adequate level. 3

Drug Interactions to Address

If your patient is on warfarin, reduce the dose by one-third to one-half immediately and check INR at least weekly—amiodarone predictably doubles anticoagulation effects. 4 If on digoxin, reduce the dose by 50% as digoxin levels will double. 4