What is the recommended management for a patient with paroxysmal supraventricular tachycardia who remains in tachycardia after an adequate dose of adenosine?

Management of PSVT Refractory to Adenosine

If adenosine fails to convert PSVT after appropriate dosing (6 mg followed by up to two 12 mg boluses), the next step is to administer a longer-acting AV nodal blocking agent—specifically intravenous diltiazem (15–20 mg over 2 minutes) or a beta-blocker (metoprolol 2.5–5 mg every 2–5 minutes)—provided the patient remains hemodynamically stable and does not have contraindications such as heart failure, hypotension, or pre-excited atrial fibrillation. 1

Initial Considerations Before Escalating Therapy

• Verify adequate adenosine administration: Adenosine must be given as a rapid IV push through a large proximal vein (antecubital preferred) followed immediately by a 20 mL saline flush to reach the heart before its <10-second half-life expires. 2
• Confirm appropriate dosing sequence: The standard protocol is 6 mg, then 12 mg (if no conversion within 1–2 minutes), then a second 12 mg dose if needed—yielding a maximum cumulative dose of 30 mg. 2
• Consider patient-specific factors that reduce adenosine efficacy: Patients taking theophylline, caffeine, or theobromine may require higher doses; conversely, those on dipyridamole or carbamazepine, or with transplanted hearts, require reduced initial doses (3 mg). 2
• Reassess hemodynamic stability: If the patient develops hypotension, altered mental status, chest pain with ischemic changes, or acute heart failure at any point, proceed immediately to synchronized cardioversion rather than additional pharmacologic therapy. 3

Second-Line Pharmacologic Options for Adenosine-Refractory PSVT

Calcium Channel Blockers (Preferred Alternative)

• Intravenous diltiazem is the most effective second-line agent, achieving conversion in 64–98% of PSVT cases, particularly AVNRT. 2
• Dosing: Administer 15–20 mg (approximately 0.25 mg/kg) IV over 2 minutes; the FDA label indicates peak therapeutic effects occur within 3–5 minutes. 4
• Verapamil is an acceptable alternative: Give 2.5–5 mg IV over 2 minutes, with effects appearing within 3–5 minutes. 1, 5
• Critical safety warnings for calcium channel blockers:
  • Do NOT use if ventricular tachycardia cannot be excluded (wide-complex tachycardia of uncertain origin). 2
  • Do NOT use in pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White syndrome), as AV nodal blockade can enhance accessory pathway conduction and precipitate ventricular fibrillation. 1, 3
  • Do NOT use in patients with suspected systolic heart failure or severe left ventricular dysfunction, as negative inotropic effects can precipitate cardiovascular collapse. 2, 3

Beta-Blockers (Alternative Option)

• Intravenous metoprolol: Administer 2.5–5 mg every 2–5 minutes up to a total of 15 mg over 10–15 minutes. 1
• Intravenous esmolol is useful for short-term control, particularly when concurrent hypertension is present. 2
• Caution: Beta-blockers are less effective than calcium channel blockers for PSVT conversion and should be avoided in hemodynamically unstable patients due to risk of worsening hypotension. 2, 3

Synchronized Cardioversion for Pharmacologic-Resistant Cases

• If both adenosine and longer-acting AV nodal blockers fail, or if pharmacologic therapy is contraindicated, proceed to elective synchronized cardioversion. 2
• Cardioversion achieves near-100% termination of AVNRT and AVRT in hemodynamically stable patients. 2
• Initial energy: Use 50–100 J for the first shock. 3
• Provide procedural sedation if the patient is conscious. 3

Diagnostic Considerations During Management

• Obtain a 12-lead ECG during tachycardia to differentiate PSVT mechanisms and exclude ventricular tachycardia or pre-excited atrial fibrillation. 2
• Adenosine has diagnostic value even when it fails to convert: It may unmask underlying atrial flutter or atrial tachycardia by transiently blocking the AV node, revealing the underlying atrial rhythm. 2
• If adenosine reveals atrial flutter or atrial tachycardia, a longer-acting AV nodal blocker (diltiazem or beta-blocker) is appropriate for rate control rather than rhythm conversion. 1, 2

Common Pitfalls and How to Avoid Them

• Pitfall: Using calcium channel blockers in wide-complex tachycardia of uncertain origin. Always assume ventricular tachycardia until proven otherwise; calcium channel blockers can cause hemodynamic collapse in VT. 2
• Pitfall: Administering AV nodal blockers in pre-excited atrial fibrillation. This can be fatal—if you suspect WPW syndrome (delta waves on baseline ECG, young patient with recurrent PSVT), avoid adenosine, calcium channel blockers, beta-blockers, and digoxin. Use procainamide or cardioversion instead. 1, 3
• Pitfall: Inadequate adenosine administration technique. Distal IV sites or slow pushes result in drug degradation before reaching the heart; always use proximal access and rapid push with immediate saline flush. 2
• Pitfall: Failing to have cardioversion equipment immediately available. Adenosine can precipitate atrial fibrillation (1–15% incidence) that may conduct rapidly in patients with accessory pathways, potentially triggering ventricular fibrillation. 6

Post-Conversion Management

• Monitor continuously for recurrence: Patients commonly experience premature atrial or ventricular complexes post-conversion that may reinitiate PSVT. 2
• If immediate recurrence occurs, consider prophylactic antiarrhythmic therapy or a longer-acting AV nodal blocker to prevent acute reinitiation. 2, 3
• Long-term management: After acute conversion, discuss definitive therapy options with the patient, including catheter ablation (first-line for preventing recurrence) versus chronic pharmacologic therapy with oral beta-blockers, diltiazem, or verapamil. 2

Special Populations

• Pregnancy: Adenosine remains safe and effective; if adenosine fails and the patient is hemodynamically stable, calcium channel blockers are reasonable. If unstable, proceed to cardioversion. 2, 6
• Asthma/COPD: Adenosine is absolutely contraindicated due to risk of severe bronchospasm. Use IV diltiazem (15–20 mg over 2 minutes) as first-line pharmacologic therapy instead. 2
• Heart transplant recipients: Require reduced initial adenosine dose (3 mg) due to denervation hypersensitivity; if adenosine fails, calcium channel blockers are appropriate if no contraindications exist. 2