How should amiodarone be dosed and used in a patient with paroxysmal supraventricular tachycardia, and what are the first‑line treatments?

Amiodarone for PSVT: A Third-Line Agent Reserved for Refractory Cases

Amiodarone should NOT be used as a first-line treatment for PSVT; it is reserved exclusively for refractory cases after failure of vagal maneuvers, adenosine, calcium channel blockers, and beta-blockers, or when these safer alternatives are contraindicated. 1, 2

First-Line Treatment Algorithm for Acute PSVT

Step 1: Vagal Maneuvers

• Attempt Valsalva maneuver or carotid sinus massage immediately, which terminates up to 25% of PSVT episodes 1
• Valsalva is safer and more efficacious than carotid massage, especially in elderly patients 3

Step 2: Adenosine (Primary Pharmacologic Agent)

• Administer 6 mg IV rapid push through a large antecubital vein followed by 20 mL saline flush 1
• If no conversion within 1-2 minutes, give 12 mg rapid IV push using the same technique 1
• Adenosine has faster onset and fewer severe side effects than calcium channel blockers 1
• Have a defibrillator available due to risk of precipitating atrial fibrillation with rapid ventricular response in WPW patients 1, 2

Step 3: Calcium Channel Blockers or Beta-Blockers

• If adenosine fails, use IV diltiazem (15-20 mg over 2 minutes) or verapamil (2.5-5 mg over 2 minutes) as reasonable alternatives with Class IIa recommendations 1, 2
• Diltiazem achieves 64-98% conversion rates in clinical trials 2
• IV beta-blockers (metoprolol, esmolol) are also reasonable Class IIa alternatives 1, 2
• Never combine IV calcium channel blockers with IV beta-blockers without careful monitoring due to potentiated hypotension and bradycardia risk 2

Step 4: Electrical Cardioversion

• Synchronized cardioversion is mandatory for hemodynamically unstable patients when pharmacologic therapy fails or is not feasible 1
• Also indicated for stable patients when all pharmacologic options have failed 1

When Amiodarone May Be Considered

Clinical Scenarios for Amiodarone Use

• Refractory PSVT after documented failure of adenosine, calcium channel blockers, and beta-blockers 1, 2
• Patients with structural heart disease or left ventricular dysfunction where calcium channel blockers are contraindicated 1, 2, 4
• Heart failure patients requiring rhythm control, as amiodarone has low pro-arrhythmic risk and neutral mortality effects in reduced LVEF 4

Amiodarone Dosing for Acute PSVT

• IV amiodarone: 5 mg/kg infused over 15-20 minutes 1, 5
• In one electrophysiology study, this regimen terminated PSVT in 7 of 9 patients (78% success rate) 1
• Alternative dosing: 300 mg IV over 1 hour, or in life-threatening situations, over 15 minutes with possible repeat after 1 hour 1
• Mean effective dose in clinical studies was 220 mg for PSVT (lower than the 340 mg needed for atrial fibrillation) 6
• Mean time to conversion: 1.2 ± 1.2 hours for PSVT 6

Loading Regimen for Ongoing Management

• Oral loading: 600 mg/day for one month OR 1000 mg/day for one week 1
• Maintenance dose: 200-400 mg/day 1
• Amiodarone prevented recurrence and inducibility in all patients after 66 ± 24 days of treatment in one study 1

Critical Safety Considerations

Why Amiodarone Is Not First-Line

• Slower onset of action compared to adenosine (30 minutes vs. seconds) 1
• Potential pro-arrhythmic risks favor safer alternatives 1
• Substantial long-term toxicity: pulmonary fibrosis, hepatic injury, bradycardia, heart block, QT prolongation 4
• 18% discontinuation rate due to adverse effects after mean 468 days 1, 4

Amiodarone Safety Profile

• Low torsades de pointes risk (<2%) despite QTc prolongation, making it the safest antiarrhythmic in structural heart disease 4
• No significant adverse effects in acute use except transient first-degree AV block in 2% of patients 6
• Safe in acute myocardial infarction and heart failure where other antiarrhythmics are contraindicated 6

Contraindications and Pitfalls

• Do not use amiodarone as first-line when safer, more effective agents are available 2
• Never delay synchronized cardioversion in unstable patients to administer amiodarone 2
• Avoid in patients who can tolerate calcium channel blockers or beta-blockers, as these have better safety profiles 1

Ongoing Management Hierarchy

For patients requiring chronic suppression who are not candidates for catheter ablation:

1. First-line oral agents: verapamil, diltiazem, or beta-blockers (Class I recommendation) 1
2. Second-line: flecainide or propafenone in patients without structural heart disease (Class IIa) 1
3. Third-line: sotalol or dofetilide (Class IIb) 1
4. Last-resort: digoxin or amiodarone (Class IIb) due to toxicity profiles 1

Catheter ablation of the slow pathway achieves 96.1% success with only 1% risk of AV block, making it the definitive treatment for recurrent PSVT 1