What is the management approach for Supraventricular Tachycardia (SVT) with aberrancy?

Management of SVT with Aberrancy

Treat SVT with aberrancy (wide-complex SVT) as ventricular tachycardia until proven otherwise, and if the patient is hemodynamically unstable, proceed immediately to synchronized cardioversion at 50-100J. 1, 2

Critical First Step: Distinguish Hemodynamic Stability

The immediate management hinges entirely on whether the patient shows signs of hemodynamic compromise:

• Hemodynamically unstable (hypotension, altered mental status, shock, chest pain, acute heart failure): Proceed directly to synchronized cardioversion without delay 1, 2
• Hemodynamically stable: You have time for diagnostic evaluation and stepwise pharmacologic intervention 1, 2

Hemodynamically Unstable Patients

Synchronized cardioversion is mandatory and should be performed immediately without attempting vagal maneuvers or pharmacologic therapy first. 1, 2

• Initial energy: 50-100J for SVT 2
• Success rate: Essentially 100% in restoring sinus rhythm 1, 2
• Perform after adequate sedation/anesthesia when time permits, but do not delay if the patient is critically unstable 1

Critical Pitfall

If adenosine was attempted before recognizing instability and the rhythm converts to atrial fibrillation with rapid ventricular response, this can precipitate ventricular fibrillation, especially if an accessory pathway is present. 1, 2 Electrical cardioversion equipment must be immediately available whenever adenosine is administered. 1

Hemodynamically Stable Patients

Step 1: Obtain 12-Lead ECG During Tachycardia

This is essential before administering any AV nodal blocking agents. 2, 3 You must identify:

• QRS duration >120 ms (confirms wide-complex tachycardia) 2
• Evidence of pre-excitation or accessory pathway conduction 1, 2
• Regularity of rhythm 1, 2

Step 2: Attempt Vagal Maneuvers

• Modified Valsalva maneuver: 31-43% success rate 2, 3
• Overall success rate for vagal maneuvers: 27.7% 2
• Safe initial intervention that avoids medication risks 2, 3

Step 3: Adenosine (If Vagal Maneuvers Fail)

Adenosine 6 mg IV rapid bolus through a proximal/large vein, followed immediately by saline flush 2, 3

• If ineffective, give 12 mg IV rapid bolus (significantly higher conversion rate: 54.2% vs 40.6% for 6 mg, p=0.03) 3
• Success rate for AVNRT/AVRT: 90-95% 1, 2, 3
• Expected side effects (30% of patients): chest discomfort, shortness of breath, flushing, lasting <1 minute 1, 4

Critical Warnings for Adenosine

Do NOT use adenosine if you suspect pre-excited atrial fibrillation (irregular wide-complex tachycardia with varying QRS morphology). 2, 3 Adenosine can precipitate atrial fibrillation that conducts rapidly down an accessory pathway, potentially causing ventricular fibrillation. 1, 2

Step 4: Alternative Pharmacologic Agents (If Adenosine Fails)

For regular wide-complex tachycardia of uncertain etiology, avoid AV nodal blocking agents (verapamil, diltiazem, beta-blockers) until you definitively exclude ventricular tachycardia or pre-excited AF. 1, 2, 3

If you are certain the rhythm is SVT with aberrancy (not VT):

• IV diltiazem or verapamil: 64-98% success rate 1, 2
  • Administer slowly over 20 minutes to minimize hypotension 1
  • Contraindicated in systolic heart failure 1
• IV beta-blockers (metoprolol, esmolol): Reasonable alternative with excellent safety profile 1, 3
  • Less effective than calcium channel blockers but safer in uncertain diagnoses 1

Absolute Contraindications to AV Nodal Blockers

Never give verapamil, diltiazem, or beta-blockers if:

• You cannot definitively exclude VT (may cause hemodynamic collapse) 1, 2, 3
• Pre-excited AF is possible (may accelerate ventricular rate and precipitate ventricular fibrillation) 1, 2

Step 5: Synchronized Cardioversion (If Medications Fail)

Even in hemodynamically stable patients, if pharmacologic therapy is ineffective or contraindicated, proceed to synchronized cardioversion. 1

Special Consideration: Pre-Excited Atrial Fibrillation

If the wide-complex tachycardia is irregular and you suspect pre-excited AF:

Hemodynamically Unstable

• Immediate synchronized cardioversion 1, 2

Hemodynamically Stable

• Ibutilide or IV procainamide are the drugs of choice 1, 2
• These agents slow conduction over the accessory pathway and may terminate AF 1
• Absolutely avoid: adenosine, diltiazem, verapamil, beta-blockers 1, 2

Post-Conversion Management

After successful cardioversion (electrical or pharmacologic):

• Patients often have atrial or ventricular premature complexes that may reinitiate tachycardia 1
• An antiarrhythmic drug may be required to prevent acute reinitiation 1
• Arrange cardiology follow-up for consideration of catheter ablation (94.3-98.5% single-procedure success rate) to prevent recurrence 3, 5

Common Pitfalls in SVT with Aberrancy

1. Assuming all wide-complex tachycardias are VT: While this is the safest assumption, true SVT with aberrancy exists, particularly in patients with known bundle branch block or post-cardiac surgery (e.g., tetralogy of Fallot repair with baseline RBBB) 1

2. Giving calcium channel blockers empirically: This can be fatal if the rhythm is actually VT or pre-excited AF 1, 2, 3

3. Delaying cardioversion in unstable patients: Median time to cardioversion in simulation studies was 8.9 minutes, far exceeding recommended immediate intervention 6

4. Failing to assess hemodynamic status properly: 60% of providers in simulation failed to assess perfusion, and 30% failed to assess mental status 6