Management of SVT Non-Responsive to Adenosine
For hemodynamically stable patients with SVT that fails to convert after 3 doses of adenosine, the next step is intravenous calcium channel blockers (diltiazem or verapamil) or IV beta blockers, followed by synchronized cardioversion if pharmacologic therapy fails. 1
Immediate Assessment
First, reassess hemodynamic stability – if the patient has become unstable (hypotension, altered mental status, chest pain, signs of shock, or acute heart failure), proceed immediately to synchronized cardioversion without further pharmacologic attempts. 1, 2
Verify the rhythm is truly regular narrow-complex SVT – adenosine's failure may indicate misdiagnosis (atrial fibrillation, atrial flutter, or atrial tachycardia rather than AVNRT/AVRT). 3 The transient AV block from adenosine should have unmasked the underlying atrial rhythm on the rhythm strip. 3
Ensure defibrillator availability before proceeding with any additional pharmacologic therapy. 3
Pharmacologic Options for Stable Patients
First-Line After Adenosine Failure
Intravenous calcium channel blockers are the preferred next step:
Diltiazem or verapamil (Class IIa recommendation) can be effective for acute treatment in hemodynamically stable SVT. 1
Slow infusion of calcium channel blockers demonstrates 98% conversion rates and superior efficacy compared to adenosine in some studies. 4
Critical contraindication: Never use calcium channel blockers if there is any evidence of ventricular pre-excitation (delta waves, WPW syndrome) on prior ECGs, as this can precipitate ventricular fibrillation in pre-excited atrial fibrillation. 5, 2
Intravenous beta blockers are reasonable alternatives (Class IIa recommendation) for acute treatment in hemodynamically stable patients. 1
Considerations for Adenosine-Refractory Cases
Higher adenosine doses (18-36 mg) may be considered in consultation with cardiology/electrophysiology, particularly in patients with impaired venous return (right heart failure, pulmonary hypertension) where standard dosing may be inadequate. 6, 7 However, this is not guideline-recommended and requires expert consultation.
Verify IV access quality – intraosseous administration of adenosine is unreliable and may explain apparent treatment failure. 8
Synchronized Cardioversion
If pharmacologic therapy is ineffective or contraindicated, synchronized cardioversion is recommended (Class I recommendation) for hemodynamically stable patients. 1
Cardioversion is highly effective in terminating SVT and avoids complications of additional antiarrhythmic drugs. 1
Perform after adequate sedation/anesthesia in stable patients. 1
Be prepared for atrial or ventricular premature complexes immediately post-cardioversion that may reinitiate tachycardia, potentially requiring antiarrhythmic drugs to prevent recurrence. 1
Critical Pitfalls to Avoid
Never use AV nodal blockers in irregular wide-complex tachycardia or suspected pre-excited atrial fibrillation – this can accelerate ventricular rate and cause ventricular fibrillation. 5, 3
Do not delay cardioversion in unstable patients to attempt additional pharmacologic interventions. 1
Obtain 12-lead ECG in sinus rhythm after conversion to evaluate for pre-excitation patterns (delta waves) that would change ongoing management. 5, 2
Post-Conversion Management
Refer all symptomatic patients to cardiac electrophysiology for consideration of catheter ablation, which has 94-98% success rates and provides definitive treatment. 5, 2
Consider oral beta blockers, diltiazem, or verapamil for ongoing management if ablation is not pursued, ensuring no ventricular pre-excitation is present. 1, 2