What is the role of Amiodarone (antiarrhythmic medication) in the treatment of Supraventricular Tachycardia (SVT)?

Amiodarone for SVT: A Last-Resort Agent

Amiodarone should be reserved as a last-line therapy for SVT only when patients cannot undergo catheter ablation and have failed all other pharmacological options including beta blockers, calcium channel blockers (diltiazem/verapamil), and class Ic agents (flecainide/propafenone). 1

Position in Treatment Algorithm

First-Line Therapies (Use These First)

• Vagal maneuvers should be attempted initially for acute episodes 1
• Adenosine is the preferred acute pharmacological treatment 1
• Catheter ablation is the definitive treatment and should be strongly considered before committing to long-term drug therapy 1

Second-Line Pharmacological Options (Before Amiodarone)

• Beta blockers, diltiazem, or verapamil for ongoing management 1
• Flecainide or propafenone in patients without structural heart disease 1
• Sotalol or dofetilide if the above are ineffective 1

When Amiodarone May Be Considered (Class IIb Recommendation)

Oral amiodarone receives only a Class IIb recommendation (may be considered) with Level C-LD evidence for ongoing SVT management, indicating weak support for its use. 1

The specific criteria are:

• Patient is not a candidate for catheter ablation OR refuses ablation 1
• AND all of the following have failed or are contraindicated: beta blockers, diltiazem, verapamil, flecainide, propafenone, sotalol, AND dofetilide 1

Why Amiodarone Is Not Preferred for SVT

Limited Efficacy Evidence

• Evidence for amiodarone in SVT comes only from small retrospective studies showing effectiveness in suppressing AVNRT 1
• The ACC/AHA/HRS guidelines explicitly state that amiodarone is a "second-line agent" due to toxicity concerns 1

Significant Toxicity Profile

The long-term toxicity burden makes amiodarone particularly problematic for SVT, which is typically not life-threatening:

Common adverse effects (occurring in 50-69% of patients): 2, 3, 4

• Tremor or ataxia (35%) 2
• Nausea and anorexia (8%) 2
• Visual disturbances - halos or blurring (6%) 2
• Thyroid dysfunction (6-17%) 2, 4
• Pulmonary interstitial infiltrates (5%) 2

Serious toxicity requiring drug discontinuation: 3, 4

• 10-26% of patients must stop amiodarone due to adverse effects 2, 3
• Interstitial pneumonitis 4
• Hepatitis 4
• Proarrhythmia (incessant ventricular tachycardia) 4
• Sinus node arrest when combined with digoxin 4

Long-term tolerance is poor:

• Only 19% of patients remain alive and continuing amiodarone therapy at 50 months 3
• While effective, "few patients tolerated the drug on a long-term basis" 3

Drug Interactions

• Increases digoxin levels significantly 4
• Potentiates warfarin anticoagulation 4

Special Populations

Pregnant Patients

Intravenous amiodarone receives Class IIb recommendation for acute treatment in pregnancy, but only for potentially life-threatening SVT when other therapies fail. 1

Critical concerns in pregnancy:

• Fetal hypothyroidism occurs in approximately 17% of cases 1
• Multiple adverse fetal effects reported 1
• Should only be used for short-term intravenous infusion in life-threatening situations 1
• Oral amiodarone for ongoing management may be considered only when highly symptomatic, recurrent SVT requires treatment and all other therapies have failed 1

Pediatric Patients

Amiodarone may be considered for refractory SVT in children with careful hemodynamic monitoring during slow IV infusion. 1

However, important caveats exist:

• 71% of children experience cardiovascular side effects (dose-related) 1
• Rare but serious complications include bradycardia, hypotension, cardiovascular collapse, and polymorphic VT 1
• Procainamide had significantly higher success rates than amiodarone for refractory pediatric SVT with equal adverse effects 1
• Most pediatric studies showing amiodarone effectiveness involved postoperative junctional tachycardia, limiting generalizability to typical SVT 1

Adult Congenital Heart Disease (ACHD)

Amiodarone may be reasonable for prevention of recurrent atrial tachycardia or atrial flutter in ACHD patients when other medications and catheter ablation are ineffective or contraindicated (Class IIb). 1

Specific concerns in ACHD:

• Thyroid disorders occur in 13-36% of ACHD patients on amiodarone 1
• Risk factors for thyrotoxicosis include female sex, cyanotic heart disease, low BMI, prior Fontan procedure, or doses >200 mg daily 1
• Use minimal effective chronic dosage 1
• Recommended for short-term use only or when no alternative exists 1

Clinical Pitfalls to Avoid

1. Do not use amiodarone as first-line therapy - The guidelines are clear that multiple other agents should be tried first 1

2. Do not overlook catheter ablation - This provides definitive cure and should be discussed before committing patients to long-term amiodarone with its toxicity burden 1

3. Do not combine with digoxin without monitoring - Risk of sinus node arrest with depression of escape foci 4

4. Do not use in pregnancy except for life-threatening situations - The 17% fetal hypothyroidism risk is unacceptable for routine SVT management 1

5. Do not forget that SVT is rarely life-threatening - The risk-benefit calculation for amiodarone's significant toxicity profile does not favor its use in most SVT cases 1, 5

Practical Recommendation

For the vast majority of SVT patients, amiodarone should never be reached in the treatment algorithm. Catheter ablation offers >90% success rates with minimal risk and should be pursued before subjecting patients to amiodarone's toxicity burden. 1 If a patient truly cannot undergo ablation and has failed all other medications, amiodarone may be considered, but this represents an uncommon clinical scenario. 1

The one exception where amiodarone has a more established role is in acute heart failure with poorly tolerated SVT where it may be preferred for rate control and is generally well tolerated hemodynamically in the acute setting. 1