What are the guidelines for managing supraventricular tachycardia (SVT) in a patient?

Management of Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers immediately in hemodynamically stable patients, followed by IV adenosine if unsuccessful, and proceed directly to synchronized cardioversion for any patient showing hemodynamic instability. 1

Initial Assessment and Stabilization

Assess hemodynamic stability first by evaluating for altered consciousness, hypotension (systolic BP <90 mmHg), chest pain, acute heart failure symptoms, or signs of shock. 2, 1 Obtain a 12-lead ECG immediately to differentiate the tachycardia mechanism and confirm whether the AV node is part of the reentrant circuit. 1, 3

For Hemodynamically Unstable Patients

Perform immediate synchronized cardioversion - this is a Class I recommendation with the highest level of evidence. 2, 1 Cardioversion successfully restores sinus rhythm in 100% of hemodynamically unstable SVT patients who failed vagal maneuvers and pharmacological therapy. 2 Do not delay for medication trials when the patient shows signs of shock, hypotension, altered mental status, or acute heart failure. 2

Acute Management for Hemodynamically Stable Patients

First-Line: Vagal Maneuvers

The modified Valsalva maneuver is the most effective vagal technique and should be performed first. 1, 4 Have the patient lie supine, bear down against a closed glottis for 10-30 seconds (generating at least 30-40 mmHg intrathoracic pressure), then immediately lie flat with legs raised. 2, 3, 4 The modified Valsalva has a 5.47-fold higher success rate compared to carotid sinus massage. 4

Alternative vagal maneuvers include:

• Carotid sinus massage: After confirming absence of carotid bruit, apply steady pressure over the carotid sinus for 5-10 seconds. 2
• Diving reflex: Apply an ice-cold, wet towel to the face. 2

The overall success rate when switching between vagal techniques reaches 27.7%. 2

Second-Line: Adenosine

IV adenosine is the first-line pharmacological agent with a 90-95% conversion rate for AVNRT and orthodromic AVRT. 1, 3 Administer 6 mg as a rapid IV bolus followed immediately by saline flush. 3 If unsuccessful after 1-2 minutes, give 12 mg, then another 12 mg if needed. 1 Adenosine serves both therapeutic and diagnostic purposes, terminating AVNRT in approximately 95% of patients and unmasking atrial activity in other arrhythmias like atrial flutter. 2

Third-Line: Calcium Channel Blockers or Beta Blockers

IV diltiazem or verapamil are highly effective alternatives, terminating SVT in 64-98% of patients. 2 These agents are particularly useful for patients who cannot tolerate beta blockers or experience recurrence after adenosine conversion. 2 Administer slowly over up to 20 minutes to minimize hypotension risk. 2

Critical contraindications for calcium channel blockers:

• Ventricular tachycardia (may cause hemodynamic collapse) 2, 1
• Pre-excited atrial fibrillation (may accelerate ventricular rate leading to ventricular fibrillation) 2, 1
• Systolic heart failure 2, 1
• Severe conduction abnormalities 2, 1

IV beta blockers are reasonable alternatives with an excellent safety profile, though evidence shows diltiazem is more effective. 2

Fourth-Line: Synchronized Cardioversion

For stable patients refractory to pharmacological therapy, synchronized cardioversion is highly effective and should be performed after adequate sedation or anesthesia. 2 Most stable patients respond to medications (80-98% success rate), but cardioversion becomes necessary in rare resistant cases. 2

Long-Term Management

First-Line: Catheter Ablation

Catheter ablation is recommended as first-line therapy for recurrent symptomatic SVT, with single-procedure success rates of 94.3-98.5%. 1, 5 This curative approach is preferred for patients with frequent symptomatic episodes, medication intolerance or ineffectiveness, or patient preference for non-pharmacological treatment. 3, 5

Pharmacological Suppression

Beta blockers are the first-line oral medication for long-term prevention in patients without ventricular pre-excitation. 1, 3 Calcium channel blockers (diltiazem or verapamil) serve as alternatives. 1, 3

For paroxysmal SVT in patients without structural heart disease, flecainide may be used starting at 50 mg every 12 hours, increased in 50 mg increments every 4 days up to a maximum of 300 mg/day. 6 However, flecainide carries proarrhythmic risk and should be reserved for cases where benefits outweigh risks. 6

Special Populations

Pregnancy

Vagal maneuvers and adenosine are first-line treatments during pregnancy due to adenosine's short half-life and safety profile. 1, 3 Synchronized cardioversion can be performed safely at all stages of pregnancy when medications fail. 1, 3

Pre-Excited Atrial Fibrillation (Wolff-Parkinson-White)

Avoid AV nodal blocking agents (adenosine, calcium channel blockers, beta blockers, digoxin) as they may accelerate ventricular rate and precipitate ventricular fibrillation. 1

For hemodynamically unstable patients: Immediate synchronized cardioversion. 1

For hemodynamically stable patients: IV ibutilide or procainamide. 1

Congenital Heart Disease

Flecainide is contraindicated due to increased risk of proarrhythmia and sudden death. 1

Multifocal Atrial Tachycardia (MAT)

Verapamil is preferred for ongoing management as it does not exacerbate pulmonary disease. 2 Diltiazem is reasonable but lacks data in MAT patients. 2 Metoprolol is reasonable after correction of hypoxia and acute decompensation, even in patients with severe pulmonary disease. 2

Common Pitfalls

• Never use calcium channel blockers or beta blockers if VT cannot be excluded - this may cause cardiovascular collapse. 2
• Never use AV nodal blockers in pre-excited atrial fibrillation - this accelerates ventricular rate. 1
• Do not delay cardioversion in unstable patients to attempt medication trials. 2
• Avoid eyeball pressure - this technique is potentially dangerous and abandoned. 2
• Ensure proper Valsalva technique - the modified version with leg raise significantly improves success rates over standard technique. 4