What are the treatment options for Supraventricular Tachycardia (SVT)?

Treatment of Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers as first-line treatment, specifically the modified Valsalva maneuver in the supine position with legs raised, followed by adenosine 6 mg IV push if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients. 1, 2, 3

Acute Management Algorithm

Step 1: Vagal Maneuvers (First-Line)

• Perform the modified Valsalva maneuver: Patient bears down against a closed glottis for 10-30 seconds (equivalent to 30-40 mm Hg intrathoracic pressure), then immediately lies flat with legs raised 1, 2, 4
• The modified technique achieves 43% conversion rate compared to only 17% with standard Valsalva 4, 5
• Alternative vagal maneuvers include carotid sinus massage (5-10 seconds of steady pressure after confirming absence of bruit) or applying ice-cold wet towel to face 1, 3
• Switching between vagal maneuver techniques increases overall success to 27.7% 1, 3
• Critical pitfall: Never apply pressure to the eyeball—this practice is dangerous and abandoned 3

Step 2: Adenosine (First-Line Medication)

• Administer 6 mg rapid IV bolus through large antecubital vein followed by 20 mL saline flush 1, 2
• If no conversion within 1-2 minutes, give 12 mg rapid IV push 1
• Adenosine terminates AVNRT in 90-95% of patients 1, 2, 3
• Dose adjustments: Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access 1
• Larger doses may be required for patients with significant theophylline, caffeine, or theobromine levels 1
• Contraindication: Do not give to patients with asthma 1
• Have defibrillator available when administering adenosine due to possibility of initiating atrial fibrillation with rapid ventricular rates in patients with WPW 1

Step 3: Alternative Pharmacologic Agents (If Adenosine Fails)

• IV diltiazem or verapamil are particularly effective for converting AVNRT to sinus rhythm in hemodynamically stable patients 1, 3
• IV beta blockers are reasonable but less effective than calcium channel blockers 1, 3
• Critical contraindications: Avoid diltiazem, verapamil, and beta blockers in patients with suspected VT, pre-excited AF, or systolic heart failure—these patients may develop ventricular fibrillation 1, 3

Step 4: Synchronized Cardioversion

• For hemodynamically unstable patients: Perform synchronized cardioversion immediately when adenosine and vagal maneuvers fail or are not feasible 1, 3
• For hemodynamically stable patients: Use synchronized cardioversion when pharmacological therapy fails or is contraindicated 1
• Initial biphasic energy dose: 50-100 J for SVT (120-200 J for atrial fibrillation), increase stepwise if initial shock fails 1
• Monophasic waveforms should begin at 200 J 1

Special Populations and Considerations

Pre-Excitation/WPW Syndrome

• Avoid all AV nodal blocking agents (verapamil, diltiazem, beta-blockers, adenosine for sustained arrhythmias) as they may accelerate ventricular rate and cause ventricular fibrillation 3
• For hemodynamically stable pre-excited AF: Use IV procainamide or ibutilide 2, 3
• For hemodynamically unstable pre-excited AF: Immediate synchronized cardioversion 3

Pregnancy

• Vagal maneuvers remain safe and first-line 2
• Adenosine is safe due to short half-life 2
• Synchronized cardioversion can be performed safely at all stages of pregnancy if necessary 2

Long-Term Management

Pharmacologic Prevention

• Beta blockers are first-line for long-term prevention of recurrent SVT 2, 3
• Calcium channel blockers (diltiazem or verapamil) are alternative first-line agents 2, 3
• For patients without structural heart disease who are not ablation candidates: Flecainide or propafenone are reasonable alternatives 3, 6
• Critical warning: Flecainide has proarrhythmic effects (13-26% incidence in sustained VT patients) and should be reserved for patients without structural heart disease, recent MI, or chronic atrial fibrillation 6

Catheter Ablation (Definitive Treatment)

• Curative option with high success rates and low complication frequency 2, 3
• Indications include: frequent symptomatic episodes, poor medication tolerance or ineffectiveness, patient preference for non-pharmacological approach, or occupational requirements 2, 3
• Provides potential cure without need for chronic pharmacological therapy 3

Patient Education

• Teach proper vagal maneuver techniques for self-management of future episodes 3
• Specifically instruct on modified Valsalva: forcefully exhale against closed airway for 10-30 seconds in supine position, then lie flat with legs raised 2, 3

Critical Diagnostic Caveat

• Always obtain 12-lead ECG to differentiate tachycardia mechanisms before treatment 2, 3
• Essential to distinguish SVT with aberrancy from ventricular tachycardia before initiating treatment 2
• Automatic tachycardias (ectopic atrial tachycardia, MAT, junctional tachycardia) are not responsive to cardioversion and require rate control with AV nodal blocking agents 1