What is the initial treatment for a patient with supraventricular tachycardia (SVT)?

Initial Treatment for Supraventricular Tachycardia

Begin with vagal maneuvers as first-line therapy, specifically the modified Valsalva maneuver performed in the supine position, followed immediately by IV adenosine if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients. 1, 2

Immediate Assessment and First-Line Intervention

Vagal Maneuvers (Class I Recommendation)

• Perform vagal maneuvers first in all hemodynamically stable patients with SVT 1, 2
• The modified Valsalva maneuver (mVM) is superior to standard techniques, achieving a 43.7% initial success rate and maintaining sinus rhythm in 28.1% of patients at 5 minutes 3, 4
• Technique: Patient lies supine, bears down against a closed glottis for 10-30 seconds (generating 30-40 mm Hg intrathoracic pressure), then immediately lies flat with legs elevated 1, 2
• Alternative maneuvers include carotid sinus massage (only after confirming absence of carotid bruits by auscultation) and applying ice-cold wet towel to the face (diving reflex) 1, 2
• Never apply pressure to the eyeball—this practice is dangerous and abandoned 1, 2

Pharmacological Treatment When Vagal Maneuvers Fail

Adenosine (Class I Recommendation)

• Administer IV adenosine immediately if vagal maneuvers fail in hemodynamically stable patients 1, 2
• Adenosine terminates AVNRT in 95% of patients and orthodromic AVRT in 90-95% of patients 1, 2
• Start with 12 mg IV adenosine rather than 6 mg—the 12 mg dose achieves significantly higher conversion rates (54.2% vs 40.6%) 5
• Have synchronized cardioversion immediately available, as adenosine may precipitate atrial fibrillation that could conduct rapidly down an accessory pathway 1

Alternative Pharmacological Agents (Class IIa Recommendation)

• If adenosine is ineffective or contraindicated, use IV diltiazem or IV verapamil 1, 2
• IV beta-blockers are also Class IIa but less effective than calcium channel blockers 1, 2
• IV amiodarone is Class IIb if other agents fail 1

Critical Pitfalls to Avoid

Pre-Excitation Recognition

• Before administering any AV nodal blocking agent, ensure the patient does not have pre-excited atrial fibrillation (irregular wide-complex tachycardia with varying QRS morphology) 1, 2
• Never give verapamil, diltiazem, beta-blockers, or adenosine to patients with pre-excited AF—these can accelerate ventricular rate and cause ventricular fibrillation 1, 2
• For hemodynamically stable pre-excited AF, use IV procainamide or ibutilide (Class I) 1, 2
• For hemodynamically unstable pre-excited AF, proceed directly to synchronized cardioversion (Class I) 1, 2

Hemodynamically Unstable Patients

Perform immediate synchronized cardioversion for any hemodynamically unstable patient with SVT 1, 2

• This is Class I recommendation when vagal maneuvers and adenosine fail or are not feasible 1
• Synchronized cardioversion is highly effective in terminating all forms of SVT 1
• Do not delay cardioversion in unstable patients to attempt multiple pharmacological agents 1

Treatment Algorithm Summary

1. Assess hemodynamic stability first 1
2. If unstable: immediate synchronized cardioversion 1
3. If stable: modified Valsalva maneuver in supine position 1, 3, 4
4. If vagal maneuvers fail: IV adenosine 12 mg 1, 2, 5
5. If adenosine fails: IV diltiazem or verapamil (unless pre-excitation suspected) 1, 2
6. If all pharmacological therapy fails: synchronized cardioversion 1

The success rate of vagal maneuvers alone is only 26-31% in real-world practice, so clinicians should be prepared to rapidly escalate to adenosine 5, 4. Documentation of vagal maneuver attempts is frequently inconsistent, but proper technique significantly impacts success rates 5.