What is the management algorithm for Supraventricular Tachycardia (SVT)?

Management Algorithm for Supraventricular Tachycardia (SVT)

Initial Assessment: Hemodynamic Stability

The first and most critical decision point is determining hemodynamic stability—if the patient is unstable (hypotensive, syncope, myocardial ischemia, or severe heart failure), proceed immediately to synchronized cardioversion without attempting vagal maneuvers or medications. 1, 2

Hemodynamically Unstable Patients

• Perform immediate synchronized cardioversion starting with 50-100 J biphasic energy, increasing stepwise if initial shock fails 2
• Do not delay for vagal maneuvers or adenosine—sinus rhythm must be promptly restored 1
• Provide adequate sedation/anesthesia before cardioversion in conscious patients 2
• Have resuscitation equipment immediately available 2

Hemodynamically Stable Patients

For stable patients, follow this stepwise algorithm:

Step 1: Vagal Maneuvers (First-Line)

The modified Valsalva maneuver (MVM) is the most effective vagal technique and should be attempted first 2, 3, 4

• Modified Valsalva technique: Patient bears down against closed glottis for 10-30 seconds (generating 30-40 mm Hg intrathoracic pressure) while supine, then immediately lies flat with legs elevated 1, 2
• MVM achieves 43.7% initial success rate and 28.1% sustained rhythm at 5 minutes—significantly superior to standard Valsalva (24.2% initial, 6.1% sustained) and carotid sinus massage (9.1% initial, 3% sustained) 3, 4
• Alternative vagal maneuvers if MVM fails: carotid sinus massage (after confirming no bruit, apply steady pressure for 5-10 seconds) or ice-cold wet towel to face 1
• Critical pitfall: Avoid eyeball pressure—this is dangerous and abandoned 1

Step 2: Adenosine (If Vagal Maneuvers Fail)

Adenosine is the next intervention with 90-95% effectiveness for terminating SVT 1, 2

• Dosing: 6 mg rapid IV push through large peripheral vein, followed immediately by 20 mL saline flush 2
• If unsuccessful, give 12 mg, then another 12 mg if needed 2
• Dose adjustments required:
  • Reduce to 3 mg for patients on dipyridamole, carbamazepine, or with transplanted heart 2
  • Larger doses needed with theophylline, caffeine, or theobromine 2
• Absolute contraindication: Asthma patients (risk of severe bronchoconstriction) 2
• Have electrical cardioversion equipment immediately available during administration 2

Step 3: Alternative Pharmacologic Agents

If adenosine fails or is contraindicated, use IV calcium channel blockers or beta blockers 1

• IV diltiazem or verapamil are reasonable alternatives with 80-98% success rates in stable patients 1
• IV beta blockers (e.g., esmolol) have excellent safety profile but are less effective than diltiazem 1
• Critical safety warnings:
  • Never use verapamil or diltiazem in wide-complex tachycardia or known accessory pathways—this can precipitate ventricular fibrillation 2
  • Avoid calcium channel blockers in systolic heart failure 1, 2
  • Must distinguish VT from SVT with aberrancy before administering AV nodal blockers 1

Step 4: Synchronized Cardioversion (If Pharmacotherapy Fails)

Synchronized cardioversion is highly effective (>95%) when medications fail in stable patients 1

• Provide adequate sedation before procedure 2
• Start with 50-100 J biphasic, increase if needed 2
• This is appropriate only for sustained SVT—not for rhythms that break or recur spontaneously 1

Special Considerations and Pitfalls

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

• If wide-complex tachycardia with known or suspected accessory pathway: Use IV procainamide if stable, or immediate cardioversion if unstable 5
• Never use AV nodal blockers (adenosine, calcium channel blockers, beta blockers)—these can cause ventricular fibrillation 2, 5

Automatic Tachycardias

• Ectopic atrial tachycardia, multifocal atrial tachycardia, and junctional tachycardia are not responsive to cardioversion 2
• These require rate control with AV nodal blocking agents, not rhythm conversion 2

Diagnostic Considerations

• Record 12-lead ECG to differentiate tachycardia mechanisms 1
• Adenosine serves dual purpose: therapeutic (terminates AVNRT/AVRT) and diagnostic (unmasks atrial activity in flutter/AT) 1
• Prehospital ECG diagnostic accuracy is 90.7%, with dangerous misdiagnosis (e.g., VT) occurring in <2% of cases 6

Unstable Patients: Adenosine vs Cardioversion Debate

• While European guidelines recommend immediate ECV for unstable patients, recent evidence suggests adenosine may be attempted first in unstable patients before ECV, potentially reducing sedation-related risks 6
• However, the ACC/AHA/HRS guidelines prioritize immediate cardioversion for hemodynamically unstable patients 1, 2, which remains the safest approach to avoid delays in rhythm restoration