What medication can prevent Supraventricular Tachycardia (SVT) without causing bradycardia?

Medication Options for SVT Prevention Without Causing Bradycardia

Flecainide is the optimal medication for preventing SVT without causing significant bradycardia in patients without structural heart disease. 1, 2

First-Line Options

Flecainide

• Dosing: Start with 50mg twice daily, can be increased to 100-200mg twice daily as needed 2
• Mechanism: Class Ic antiarrhythmic that slows conduction in cardiac tissues
• Efficacy:
  • Significantly increases time to first recurrence of SVT 1
  • 87% of PSVT patients show symptomatic improvement 3
  • 82% of patients remain free from arrhythmic attacks during long-term therapy 4
• Advantages:
  • Minimal effect on sinus node function (less likely to cause bradycardia) 2
  • Long-term efficacy maintained or improved over time 4
  • Can be used as "pill-in-the-pocket" approach for infrequent episodes 1

Propafenone

• Dosing: 150mg every 8 hours (immediate release) or 225mg every 12 hours (extended release) 1
• Mechanism: Class Ic antiarrhythmic with mild beta-blocking properties
• Efficacy: Reduces recurrence rate to one-fifth of placebo 1
• Caution: May have slightly higher risk of bradycardia than flecainide due to beta-blocking properties

Critical Precautions with Class Ic Agents

1. Absolute contraindications:

   • Structural heart disease
   • Coronary artery disease
   • Left ventricular dysfunction
   • Heart failure
   • Brugada syndrome 1

2. ECG monitoring: Watch for QRS widening >25% from baseline

3. Concomitant therapy: Often combined with AV nodal blocking agents to prevent 1:1 conduction if atrial flutter develops 1

Alternative Options (If Class Ic Agents Contraindicated)

Calcium Channel Blockers

• Diltiazem: Initial dose 15-20mg IV (0.25mg/kg), maintenance 5-15mg/hr IV 1
• Verapamil: Initial dose 2.5-5mg IV over 2 minutes, may repeat 5-10mg every 15-30 minutes 1
• Caution: More likely to cause bradycardia than Class Ic agents, especially in patients with pre-existing conduction disease

Beta Blockers

• Metoprolol: 5mg IV over 1-2 minutes, repeated to maximum 15mg 1
• Atenolol: 5mg IV over 5 minutes, repeat 5mg in 10 minutes if needed 1
• Caution: High risk of bradycardia, especially with higher doses

Amiodarone

• Dosing: 150mg over 10 minutes, followed by 1mg/min infusion for 6 hours 1
• Consideration: Complex side effect profile but can be used in structural heart disease
• Caution: May cause bradycardia, especially with long-term use

Decision Algorithm

1. Assess for structural heart disease:

   • If absent → Flecainide or propafenone (first-line)
   • If present → Consider amiodarone or catheter ablation

2. Assess frequency of episodes:

   • Frequent episodes → Daily prophylactic therapy
   • Infrequent but prolonged episodes → "Pill-in-the-pocket" approach

3. Monitor for efficacy:

   • If inadequate response at initial dose → Increase dose within safe range
   • If continued failure → Switch to alternative agent or consider ablation

Definitive Management

Catheter ablation should be considered for definitive treatment with success rates of 94-98% 5. This approach eliminates the need for chronic medication and associated risks of bradycardia.

Pitfalls to Avoid

1. Never use Class Ic agents in patients with structural heart disease due to increased mortality risk 1, 6

2. Avoid combining multiple AV nodal blocking agents (beta blockers, calcium channel blockers) as this significantly increases bradycardia risk 5

3. Don't use verapamil or diltiazem in patients with pre-excited atrial fibrillation as this can accelerate ventricular response 1

4. Monitor for proarrhythmic effects with all antiarrhythmic medications, especially at higher doses 2