What is the next step in treatment for a 58-year-old female patient with a history of mitral valve repair and Supraventricular Tachycardia (SVT), who presents to the Emergency Department (ED) with an episode of SVT that is unresponsive to adenosine?

Next Step in SVT Management After Failed Adenosine

After adenosine fails to convert SVT in a hemodynamically stable patient, administer intravenous calcium channel blockers (diltiazem or verapamil) or beta-blockers as the next-line therapy. 1

Immediate Assessment

First, confirm the patient's hemodynamic stability. Look for:

• Hypotension (systolic BP <90 mmHg)
• Altered mental status or signs of shock
• Chest pain or acute heart failure
• Heart rate >150 bpm 2

If the patient becomes hemodynamically unstable at any point, proceed immediately to synchronized cardioversion rather than additional pharmacologic therapy. 1, 2

Pharmacologic Management for Stable Patients

Calcium Channel Blockers (Preferred)

Intravenous diltiazem or verapamil are particularly effective second-line agents with conversion rates of 80-98% for hemodynamically stable SVT. 2

• These agents work by blocking AV nodal conduction, either terminating reentrant SVT or controlling ventricular rate 1
• Diltiazem has proven more effective than beta-blockers (such as esmolol) in head-to-head comparisons 1
• Both agents have longer duration of action than adenosine, providing more sustained rhythm control 1

Beta-Blockers (Alternative)

Intravenous beta-blockers are reasonable alternatives with an excellent safety profile, though they show lower efficacy than calcium channel blockers. 1

• Evidence for beta-blocker efficacy in terminating AVNRT is more limited compared to calcium channel blockers 1
• They remain a viable option, particularly in patients where calcium channel blockers may be contraindicated 1

Critical Safety Considerations

Pre-excitation Warning

Never administer calcium channel blockers or beta-blockers if there is any suspicion of pre-excitation (Wolff-Parkinson-White syndrome) on ECG, as these agents can precipitate ventricular fibrillation and death. 3, 2

• These drugs may enhance conduction over the accessory pathway 3
• If WPW is suspected, proceed directly to synchronized cardioversion or consult cardiology 1

Contraindications to Avoid

• Do not use calcium channel blockers if ventricular tachycardia is suspected, as this can cause hemodynamic collapse 1
• Avoid diltiazem or verapamil in patients with suspected systolic heart failure due to negative inotropic effects 1
• Ensure the rhythm is truly SVT and not VT with aberrancy before administering AV nodal blocking agents 1

If Pharmacologic Therapy Fails

Synchronized cardioversion is highly effective and recommended when pharmacologic therapy fails to terminate SVT in hemodynamically stable patients. 1

• Start with 0.5-1 J/kg, increasing to 2 J/kg if initial attempt unsuccessful 1
• Provide sedation when possible before cardioversion 1
• Cardioversion has proven safety and effectiveness in patients who fail vagal maneuvers and intravenous pharmacologic therapy 1

Special Consideration: Higher Adenosine Dosing

While not standard guideline recommendation, recent evidence suggests that if repeat adenosine is considered before moving to other agents, higher doses up to 24-36 mg may be effective in refractory cases, though this requires cardiology consultation 4. However, the 2025 multi-center study found that starting with 12 mg adenosine (rather than 6 mg) achieved significantly higher conversion rates (54.2% vs 40.6%), suggesting the initial adenosine dosing may have been suboptimal 5.

Long-term Management

After acute conversion, this patient with recurrent SVT and history of mitral valve repair should be:

• Monitored for recurrence 1
• Considered for oral AV nodal blocking agents (diltiazem, verapamil, or beta-blockers) for ongoing management 1, 2
• Referred to cardiology for evaluation of catheter ablation, which has 94-98% success rates for definitive treatment 2