Chronic Supraventricular Tachycardia: Evaluation and Treatment
Initial Diagnostic Evaluation
All patients with suspected chronic SVT must have a 12-lead ECG recorded during tachycardia, as this single step determines all subsequent treatment decisions. 1, 2
Critical ECG Features to Document
- QRS duration: Narrow (<120 ms) confirms SVT; wide (≥120 ms) requires differentiation from ventricular tachycardia 2
- P wave location: Buried in QRS suggests AVNRT; early ST segment suggests AVRT 2
- RP interval: Short (<90 ms) indicates typical AVNRT or AVRT; long RP suggests atrial tachycardia 2
- Rhythm regularity: Regular rhythm indicates AVNRT, AVRT, or atrial tachycardia; irregular suggests atrial fibrillation 2
- Pre-excitation (delta waves): Presence on resting ECG with any palpitation history mandates immediate electrophysiology referral due to sudden death risk 1, 2
Essential Clinical History Elements
- "Neck pounding" or "shirt flapping": Highly specific for AVNRT due to cannon A-waves 2
- Syncope during episodes: Occurs in 4% overall but more common in elderly; requires urgent cardiology referral 2
- Driving history: 57% experience episodes while driving; 14% have syncope while driving 2
- Irregular palpitations with baseline pre-excitation: Strongly suggests atrial fibrillation episodes requiring immediate electrophysiology evaluation 1, 2
Mandatory Additional Testing
- Transthoracic echocardiography: Required in all patients with documented sustained SVT to exclude structural heart disease not detectable by physical exam or ECG 1, 2
- Ambulatory monitoring strategy: 24-hour Holter if episodes occur several times per week; event/loop recorder for less frequent episodes; implantable loop recorder for rare symptoms (<2 episodes/month) with severe hemodynamic instability 1, 2
Immediate Referral Criteria
Refer immediately to cardiac electrophysiology for any of the following: 1, 2
- Pre-excitation on resting ECG with any palpitation history
- Wide complex tachycardia of unknown origin
- Syncope during tachycardia or with exercise
- Drug resistance or intolerance
- Patient preference to avoid chronic drug therapy
Acute Management
Hemodynamically Unstable Patients
Synchronized cardioversion is first-line treatment when vagal maneuvers or adenosine are ineffective or not feasible. 1
Hemodynamically Stable Patients
Follow this stepwise algorithm: 1
Vagal maneuvers (Class I recommendation): Valsalva maneuver in supine position for 10-30 seconds at 30-40 mmHg, or ice-cold wet towel to face 1
Adenosine (Class I recommendation): 95% effective for AVNRT; first-line pharmacologic agent due to rapid onset and short half-life 1, 3
Intravenous diltiazem or verapamil (Class IIa recommendation): 64-98% success rate if adenosine fails 1, 3
Intravenous beta blockers (Class IIa recommendation): Reasonable alternative if calcium channel blockers contraindicated 1
Synchronized cardioversion: If pharmacological therapy ineffective or contraindicated 1
Critical caveat: Never administer verapamil or diltiazem for wide-complex tachycardia or pre-excited atrial fibrillation, as this may cause hemodynamic collapse or ventricular fibrillation 1
Ongoing Management Strategy
Electrophysiological study with catheter ablation is the definitive first-line treatment for chronic symptomatic SVT, with 94.3-98.5% single-procedure success rate. 1, 2 This recommendation prioritizes quality of life and avoids chronic medication side effects.
When Ablation is Preferred or Declined
If patient prefers pharmacologic management or ablation is not accessible, use this medication hierarchy: 1
First-Line Pharmacologic Therapy (Class I)
- Oral beta blockers, diltiazem, or verapamil: For patients without ventricular pre-excitation 1
- Verapamil studied up to 480 mg/day with documented reduction in episode frequency and duration 1
- Patient education on vagal maneuvers: Should be taught to all patients for self-termination 1
Second-Line Options (Class IIa)
- Flecainide or propafenone: For patients without structural heart disease or ischemic heart disease 1
- Flecainide 100-300 mg/day or propafenone 450-900 mg/day shows 86-93% probability of 12-month effective treatment 1
- Absolute contraindication: Structural heart disease or ischemic heart disease due to proarrhythmia risk 1, 4
- FDA warning: Flecainide causes proarrhythmic events in 4% of SVT patients, including 2 ventricular arrhythmias (one fatal VT/VF) 4
Third-Line Options (Class IIb)
Use only when first and second-line agents ineffective or contraindicated: 1
- Sotalol: May be reasonable 1
- Dofetilide: May be reasonable 1
- Amiodarone: Consider only after all other options exhausted 1
- Digoxin: May be reasonable in patients without pre-excitation 1
Flecainide Dosing Protocol (If Used)
Start 50 mg every 12 hours; increase by 50 mg twice daily every 4 days until efficacy achieved; maximum 300 mg/day for SVT. 4 Steady-state levels require 3-5 days, so dose increases must not occur more frequently than every 4 days 4. Higher initial doses increase proarrhythmic events and heart failure risk 4.
Common Pitfalls to Avoid
- Misdiagnosing wide-complex tachycardia as SVT: Treat as ventricular tachycardia unless proven otherwise; misdiagnosis can be fatal 1, 2
- Using adenosine without caution in unclear diagnosis: May produce ventricular fibrillation in coronary artery disease patients or accelerate ventricular rate in pre-excited tachycardias 1
- Prescribing flecainide/propafenone without excluding structural heart disease: Requires echocardiography first 1, 4
- Delaying referral for pre-excitation: These patients require immediate electrophysiology evaluation regardless of symptom frequency 1, 2
- Initiating flecainide in outpatient setting for sustained VT: Must be hospital-initiated with rhythm monitoring 4