What is the initial approach to managing Supraventricular Tachycardia (SVT) in the Emergency Department (ED)?

Initial Management of Supraventricular Tachycardia in the Emergency Department

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

Immediate Assessment

Upon presentation, obtain a 12-lead ECG to confirm regular SVT and rule out ventricular tachycardia or pre-excited atrial fibrillation, as administering AV nodal blockers in these conditions can cause hemodynamic collapse or ventricular fibrillation. 1

Critical distinction: Ensure QRS duration is <120 ms and verify the patient does not have pre-excitation (delta waves), as calcium channel blockers or beta blockers are contraindicated in pre-excited atrial fibrillation. 1

Hemodynamic Status Determines Pathway

Hemodynamically Unstable Patients

Proceed immediately to synchronized cardioversion if the patient exhibits hypotension, altered mental status, signs of shock, chest pain, or acute heart failure symptoms. 1

• Cardioversion successfully restores sinus rhythm in 100% of hemodynamically unstable SVT cases when vagal maneuvers and adenosine have failed or are not feasible. 1
• Do not delay cardioversion attempting multiple pharmacologic interventions in unstable patients. 1

Hemodynamically Stable Patients

Follow this stepwise algorithm:

Step 1: Vagal Maneuvers (Class I Recommendation)

Attempt vagal maneuvers first—they are quick, safe, and achieve conversion in approximately 31% of cases. 1, 2

• Valsalva maneuver: Patient bears down against closed glottis for 10-30 seconds (equivalent to 30-40 mm Hg intrathoracic pressure) in the supine position. 1
• Carotid sinus massage: After confirming absence of carotid bruit, apply steady pressure over right or left carotid sinus for 5-10 seconds. 1
• Ice water immersion: Apply ice-cold wet towel to face (diving reflex), particularly effective in infants. 1, 3
• Valsalva is more successful than carotid massage (27.7% overall success when switching between techniques). 1

Step 2: Adenosine (Class I Recommendation)

If vagal maneuvers fail, adenosine is the next intervention with 90-95% conversion rate for AVNRT and AVRT. 1

Dosing strategy: Recent evidence suggests starting with 12 mg adenosine is more effective than 6 mg (54.2% vs 40.6% conversion rate, p=0.03), though traditional guidelines recommend 6 mg initially. 2 Given the higher efficacy and similar safety profile, consider 12 mg as initial dose in stable patients.

• Administer as rapid IV bolus via proximal vein followed immediately by saline flush. 1
• Record continuous ECG during administration to distinguish failure to convert versus immediate reinitiation. 1
• Have cardioversion equipment immediately available as adenosine may precipitate atrial fibrillation with rapid ventricular response. 1
• Common transient side effects (<1 minute): chest discomfort, dyspnea, flushing—but serious adverse effects are rare. 1

Step 3: Alternative Pharmacologic Agents (Class IIa Recommendation)

If adenosine fails or is contraindicated in stable patients:

• IV diltiazem or verapamil: Highly effective for AVNRT conversion (80-98% success). 1
  • Critical caveat: Absolutely contraindicated if any possibility of VT, pre-excited AF, or systolic heart failure—can cause ventricular fibrillation or hemodynamic collapse. 1
• IV beta blockers: Reasonable alternative with excellent safety profile, though less effective than calcium channel blockers. 1

Step 4: Synchronized Cardioversion

If pharmacologic therapy is ineffective or contraindicated in stable patients, proceed to synchronized cardioversion with appropriate sedation. 1

Common Pitfalls to Avoid

• Documentation failure: Only 26% of ED cases document attempted vagal maneuvers, suggesting underutilization of this first-line intervention. 2
• Incorrect adenosine technique: 44% of administrations use improper technique (not rapid bolus, wrong IV site, inadequate flush). 2
• Misidentifying rhythm: 20% of cases misidentify the rhythm—always obtain 12-lead ECG before treatment. 2
• Delaying cardioversion in unstable patients: Median time to cardioversion in simulation studies was 8.9 minutes when it should be immediate—delays occur from failure to assess perfusion and mental status. 4
• Using AV nodal blockers in pre-excited AF: This can accelerate ventricular rate and cause ventricular fibrillation—always check for delta waves. 1

Post-Conversion Management

After successful conversion, be prepared for immediate reinitiation of SVT from atrial or ventricular premature complexes—may require antiarrhythmic drug to prevent recurrence. 1

Educate patients on performing vagal maneuvers for future episodes and arrange cardiology follow-up for consideration of catheter ablation, which has 94.3-98.5% single-procedure success rates. 1, 5