What is the long-term medical management with dosing for a patient with recurrent paroxysmal supraventricular tachycardia (PSVT)?

Long-Term Medical Management of Recurrent Paroxysmal Supraventricular Tachycardia

For patients with recurrent PSVT who prefer medical management over catheter ablation, start with a nondihydropyridine calcium channel blocker (verapamil 360-480 mg/day) or beta-blocker (propranolol 240 mg/day or metoprolol 25-50 mg twice daily), and if these fail in patients without structural heart disease, escalate to flecainide 200-300 mg/day or propafenone 300 mg three times daily. 1, 2

First-Line Therapy: AV Nodal Blocking Agents

Standard initial therapy consists of three equally effective options:

• Verapamil 360-480 mg/day (divided dosing) has demonstrated efficacy in reducing episode frequency and duration in randomized trials, with higher doses trending toward greater effectiveness 1
• Propranolol 240 mg/day showed equivalent efficacy to verapamil in controlled studies for reducing PSVT frequency and duration 1
• Metoprolol 25-50 mg twice daily (maximum 100 mg twice daily) is recommended as a first-line beta-blocker option, particularly useful in pregnant patients 2
• Diltiazem 30-90 mg three to four times daily (typical maintenance 240 mg/day) serves as an alternative calcium channel blocker 2
• Digoxin 0.375 mg/day demonstrated similar efficacy to verapamil and propranolol in small trials, though it is less commonly used today 1

Critical safety warning: Never use calcium channel blockers (diltiazem/verapamil) in patients with pre-excitation (Wolff-Parkinson-White syndrome) or pre-excited atrial fibrillation, as this can precipitate ventricular fibrillation 2

Second-Line Therapy: Class Ic Antiarrhythmics (Patients Without Structural Heart Disease)

For patients who fail AV nodal blocking agents and have no structural heart disease:

• Flecainide 200-300 mg/day (divided dosing) completely suppressed episodes in 65% of patients and demonstrates superior long-term efficacy compared to verapamil, with 30% achieving complete symptomatic suppression versus 13% with verapamil 1
• Propafenone 300 mg three times daily (900 mg/day total) reduced recurrence rates to one-fifth that of placebo, with a relative risk of treatment failure for placebo versus propafenone of 6.8 1, 2, 3
• Starting dose for flecainide in PSVT is 50 mg every 12 hours, increased in 50 mg twice daily increments every four days until efficacy is achieved, with a maximum dose of 300 mg/day 4

Absolute contraindication: Class Ic agents (flecainide and propafenone) are strictly contraindicated in patients with structural heart disease, recent myocardial infarction, or ischemic heart disease due to increased risk of ventricular arrhythmias and proarrhythmic effects 1, 2

Important practice point: Class Ic drugs are often combined with beta-blocking agents to enhance efficacy and reduce the risk of one-to-one AV nodal conduction if atrial flutter develops 1

Third-Line Therapy: Class III Antiarrhythmics (Reserved for Specific Situations)

Class III drugs should generally be avoided due to toxicity concerns, but may be considered in select cases:

• Sotalol demonstrated superiority over placebo in prolonging time to PSVT recurrence in placebo-controlled trials 1
• Dofetilide 500 mcg twice daily showed 50% probability of complete symptomatic suppression over 6 months versus 6% with placebo, with no proarrhythmic events in the trial 1
• Amiodarone 200-400 mg/day (after loading dose of 400-600 mg daily for 2-4 weeks) is safe in patients with structural heart disease or reduced ejection fraction, where other agents are contraindicated 1, 2

Routine use of class III drugs should be avoided due to toxicities including proarrhythmia (torsades de pointes) 1

Obsolete Therapies to Avoid

Class Ia drugs (quinidine, procainamide, disopyramide) have limited appeal due to multidosing regimens, modest efficacy, and adverse/proarrhythmic effects, and are rarely used today 1

Alternative Strategy: "Pill-in-the-Pocket" Approach

For patients with infrequent but prolonged, well-tolerated episodes:

• Single-dose flecainide (approximately 3 mg/kg) can be used for acute termination when vagal maneuvers fail 1
• This approach requires patients to be free of significant LV dysfunction, sinus bradycardia, or pre-excitation 1
• This strategy obviates chronic drug exposure between rare arrhythmic events 1

Dosing Adjustments for Special Populations

In patients with severe renal impairment (creatinine clearance <35 mL/min/1.73m²), flecainide dosing requires adjustment 4

In children, flecainide dosing is weight-based: under 6 months start at 50 mg/m² body surface area daily divided into 2-3 doses; over 6 months may increase to 100 mg/m² per day, with maximum 200 mg/m² per day 4

Critical Monitoring Requirements

For flecainide therapy:

• Steady-state plasma levels may not be achieved until 3-5 days of therapy at a given dose due to the long half-life (12-27 hours) 4
• Increase dosage no more frequently than every four days 4
• Therapeutic plasma levels are 200-500 ng/mL in children, occasionally requiring up to 800 ng/mL 4

When to Abandon Medical Management

Catheter ablation should be strongly considered as it represents definitive first-line therapy with success rates of 94.3-98.5% and <1% risk of AV block, eliminating the need for chronic pharmacological therapy 5, 6, 7

Atypical AVNRT (fast-slow) represents only 5-10% of cases and may be more resistant to conventional pharmacological therapy with success rates <50%, making ablation particularly attractive in these patients 5

Predictors of drug-refractory AVNRT include hypertension, valvular heart disease, atrial vulnerability, long-lasting echo zone, and relatively slow AVNRT, warranting early electrophysiology referral 5