What is the first-line treatment for supraventricular tachycardia (SVT) using adenosine?

First-Line Treatment for Supraventricular Tachycardia with Adenosine

Adenosine 6 mg rapid IV push is the recommended first-line pharmacologic treatment for hemodynamically stable SVT after vagal maneuvers fail, with an approximately 95% success rate in terminating AVNRT. 1

Treatment Algorithm

Step 1: Initial Non-Pharmacologic Intervention

• Vagal maneuvers are the absolute first-line intervention before any medication is given 1
• Perform Valsalva maneuver (bearing down against closed glottis for 10-30 seconds at 30-40 mm Hg pressure) with patient supine 1
• If Valsalva fails, attempt carotid sinus massage for 5-10 seconds after confirming absence of bruit 1
• Alternative: apply ice-cold wet towel to face (diving reflex) 1
• Success rate of vagal maneuvers is only 27.7% when switching between techniques 1

Step 2: Adenosine Administration Protocol

Initial dose: 6 mg IV push (not 12 mg) 2

• Administer via large proximal vein as rapid bolus followed immediately by 20 mL saline flush 2
• If no conversion within 1-2 minutes, give 12 mg IV push 2
• If still no conversion, give second 12 mg IV push 2
• Success rates: 73% respond to 6 mg, 88% respond after second dose (12 mg), 99% respond after third dose 3

Why start at 6 mg instead of 12 mg? The dose-dependent side effects (flushing, chest discomfort, dyspnea) are significant, and 70% of patients convert with 6 mg or less 2. However, recent prehospital data suggests starting with 12 mg may reduce re-dosing and improve conversion rates, though guidelines still recommend 6 mg initially 4.

Step 3: Dose Modifications for Special Populations

Reduce initial dose to 3 mg for: 2

• Patients taking dipyridamole or carbamazepine
• Heart transplant recipients
• Central venous access administration

Increase dose requirements for: 2

• Patients with significant theophylline, caffeine, or theobromine blood levels

Safe in pregnancy: Adenosine is recommended as first-line pharmacologic treatment for pregnant patients with SVT 1, 2

Step 4: Monitoring and Equipment

• Have defibrillator immediately available when administering adenosine, especially if Wolff-Parkinson-White syndrome is a consideration, due to risk of precipitating atrial fibrillation with rapid ventricular rates 2
• Continuous ECG recording during administration helps distinguish drug failure from successful termination with immediate reinitiation 2

Critical Contraindications

Do NOT give adenosine to patients with: 2

• Asthma or bronchospastic lung disease (risk of severe bronchospasm)
• Second or third-degree AV block
• Sick sinus syndrome

Common Pitfalls and Side Effects

Expected transient side effects (resolve in <60 seconds): 2, 3

• Chest tightness (83% of patients) 3
• Flushing (39.4% of patients) 3
• Dyspnea 2
• Sense of impending death (7% of patients) 3

Warn patients these symptoms are coming and will resolve quickly to prevent panic.

Post-Conversion Management

• Monitor for recurrence after successful conversion 2
• If SVT recurs, re-treat with adenosine or consider longer-acting AV nodal blocking agent (diltiazem or beta-blocker) 2
• If adenosine unmasks atrial flutter or atrial tachycardia rather than terminating the rhythm, transition to longer-acting AV nodal blocking agent 2

When Adenosine Fails or is Contraindicated

For hemodynamically unstable patients: Proceed immediately to synchronized cardioversion 1

For hemodynamically stable patients when adenosine fails: 1

• Intravenous diltiazem or verapamil (avoid in suspected VT, pre-excited AF, or systolic heart failure) 1
• Intravenous beta-blockers (metoprolol, propranolol, or esmolol) 1
• Synchronized cardioversion if pharmacologic therapy fails or is contraindicated 1