What is the next best step for a patient with supraventricular tachycardia (SVT) who continues to experience palpitations despite being on flecainide (Flecainide) 75mg twice daily (BID) and Cardizem (Diltiazem) 120mg daily?

Management of Breakthrough SVT on Flecainide and Diltiazem

The next best step is to refer this patient for catheter ablation, which has a >95% success rate and <5% recurrence rate, as this represents failure of optimal medical therapy. 1

Why Current Therapy Has Failed

Your patient is on suboptimal doses of both medications:

• Flecainide 75mg BID is below the typical therapeutic range for SVT. The FDA-approved dosing for paroxysmal supraventricular arrhythmias starts at 50mg BID and can be increased to a maximum of 300mg/day (150mg BID). 2
• Diltiazem 120mg daily is also subtherapeutic for ongoing SVT management, though specific optimal dosing for chronic SVT prevention varies by patient. 3

Immediate Management Options

Option 1: Optimize Current Medical Therapy (If Ablation Declined)

Increase flecainide dose incrementally:

• Increase by 50mg BID every 4 days until efficacy is achieved, up to maximum 150mg BID (300mg/day total). 2
• Most patients with SVT respond to doses between 100-150mg BID. 1, 4
• Monitor for proarrhythmic effects and conduction abnormalities with each dose increase. 2
• Critical prerequisite: Confirm patient has NO structural heart disease or ischemic heart disease, as flecainide is contraindicated in these populations due to proarrhythmia risk. 1

Consider increasing diltiazem dose:

• Standard chronic dosing for rate control can range from 120-360mg daily (extended-release formulations). 3
• The combination of flecainide with diltiazem or a beta-blocker increases efficacy to >90% in preventing symptomatic SVT. 1

Option 2: Switch to Alternative Combination Therapy

If flecainide optimization fails or is not tolerated:

• Switch to propafenone 450-900mg/day (divided doses), which has 86% probability of 12-month effective treatment. 1
• Propafenone also requires absence of structural/ischemic heart disease. 1

If Class IC agents are contraindicated or ineffective:

• Sotalol (80-160mg BID) may be reasonable and can be used in patients with structural heart disease, though it carries proarrhythmic risk requiring careful monitoring. 1
• Dofetilide is another option but requires inpatient initiation due to QT prolongation risk. 1

Option 3: Catheter Ablation (Strongly Recommended)

This is the definitive treatment and should be strongly considered now:

• Success rate: 95% for AVNRT and AVRT. 1, 5
• Recurrence rate: <5%. 5
• Risk of inadvertent heart block: <1%. 5
• Ablation is preferred over escalating antiarrhythmic therapy in symptomatic patients, especially when initial medical therapy fails. 1

Critical Safety Considerations

Before increasing flecainide, verify:

• No structural heart disease (echocardiogram if not recently done). 1
• No ischemic heart disease (stress test or coronary evaluation if risk factors present). 1
• Normal renal function (flecainide is renally cleared; dose adjustment needed if CrCl <35 mL/min). 2
• Baseline ECG to assess QRS duration (flecainide causes dose-dependent QRS widening). 2

Monitor during dose escalation:

• ECG after each dose increase to assess QRS widening (discontinue if QRS increases >25% from baseline). 2
• Plasma trough flecainide levels if available (therapeutic range 200-500 ng/mL). 2

Patient Education

Teach vagal maneuvers for acute episode termination:

• Valsalva maneuver in supine position (forceful exhalation against closed airway for 10-30 seconds, equivalent to 30-40 mmHg). 1
• Ice-cold wet towel to face (diving reflex). 1
• These maneuvers have 27.7% overall success rate and may avoid emergency visits. 3

Common Pitfalls to Avoid

• Do not use flecainide in patients with structural heart disease (CAST trial showed increased mortality in post-MI patients with ventricular arrhythmias). 4
• Do not combine multiple AV nodal blocking agents without careful monitoring (diltiazem + beta-blocker can cause excessive bradycardia). 3
• Do not delay ablation referral in highly symptomatic patients—quality of life improves dramatically post-ablation. 6, 7
• Avoid using calcium channel blockers if Wolff-Parkinson-White syndrome is suspected (can precipitate ventricular fibrillation in pre-excited atrial fibrillation). 1, 3