What is the next step for a patient in Supraventricular Tachycardia (SVT) who does not respond to adenosine?

Management of SVT After Failed Adenosine Response

For patients with SVT who do not respond to adenosine, synchronized cardioversion is recommended if the patient is hemodynamically unstable, while intravenous calcium channel blockers (diltiazem or verapamil) or beta blockers are recommended for hemodynamically stable patients. 1, 2

Assessment of Hemodynamic Status

• Hemodynamically unstable (presence of any of the following):

  • Hypotension
  • Altered mental status
  • Signs of shock
  • Chest pain
  • Acute heart failure symptoms

• Hemodynamically stable (absence of above symptoms)

Treatment Algorithm

For Hemodynamically Unstable Patients:

1. Immediate synchronized cardioversion (Class I, LOE B-NR) 1, 2
   • Highly effective in terminating SVT
   • Shown to successfully restore sinus rhythm in all patients who failed pharmacological therapy 1

For Hemodynamically Stable Patients:

1. Intravenous calcium channel blockers (Class IIa, LOE B-R) 1

   • Diltiazem: 15-20 mg (0.25 mg/kg) IV over 2 minutes; if needed, in 15 minutes give additional 20-25 mg (0.35 mg/kg) 1
   • Verapamil: 2.5-5 mg IV bolus over 2 minutes (3 minutes in older patients); may repeat with 5-10 mg every 15-30 minutes to maximum 20 mg 1
   • Effectiveness: 64-98% termination rate for SVT 1

2. Intravenous beta blockers (Class IIa, LOE C-LD) 1, 2

   • Less effective than calcium channel blockers but have excellent safety profile 2
   • Options include esmolol, metoprolol, or propranolol

3. Higher doses of adenosine (if initial standard doses failed)

   • Consider doses of 18-24 mg if standard doses (6 mg, 12 mg) failed 3
   • Case reports document successful conversion with doses up to 36 mg in refractory cases 3

4. Synchronized cardioversion (Class I, LOE B-NR) 1

   • Indicated when pharmacological therapy is ineffective or contraindicated
   • Should be performed after adequate sedation or anesthesia in stable patients

Important Considerations and Precautions

Contraindications and Cautions:

• Calcium channel blockers (diltiazem/verapamil):

  • Avoid in patients with:
    • Suspected systolic heart failure
    • Hypotension
    • Pre-excited atrial fibrillation (can accelerate ventricular rate) 1, 2
    • Ventricular tachycardia (can cause hemodynamic collapse)

• Beta blockers:

  • Use cautiously in patients with:
    • Severe conduction abnormalities
    • Sinus node dysfunction
    • Bronchospastic disease

Diagnostic Considerations:

• Failure of adenosine may indicate:
  • Atrial flutter or atrial tachycardia (adenosine rarely terminates these) 1, 2
  • Incorrect diagnosis (not SVT)
  • Need for higher doses 3

Success Rates and Factors:

• Overall adenosine response rate is approximately 86% 4
• Factors associated with successful adenosine response:
  • History of previous SVT episodes
  • Older age 4

Follow-up Management

• After successful conversion, monitor for recurrence
• Consider long-term management options:
  • Oral medications (beta blockers, calcium channel blockers)
  • Catheter ablation for definitive treatment (95% success rate for AVNRT) 2

Remember that synchronized cardioversion is highly effective and should not be delayed in unstable patients or when pharmacological therapy fails repeatedly.