What injection can be given in an outpatient setting for tachycardia, specifically supraventricular tachycardia (SVT)?

Adenosine is the Injection of Choice for SVT in the Outpatient Setting

Adenosine is the recommended first-line injectable medication for treating supraventricular tachycardia (SVT) in the outpatient setting, following vagal maneuvers, with a Class I recommendation from the ACC/AHA/HRS guidelines. 1

Initial Management Approach

Step 1: Vagal Maneuvers First

• Attempt vagal maneuvers before any medication (Class I recommendation) 1
• Perform with patient supine: Valsalva maneuver (bearing down for 10-30 seconds) or carotid massage (5-10 seconds after confirming no bruit) 1
• Success rate approximately 27.7% when switching between techniques 1

Step 2: Adenosine Administration Protocol

If vagal maneuvers fail, adenosine is the definitive injectable treatment:

• Initial dose: 6 mg IV push (not 12 mg) via large proximal vein 2, 3
• Must be given as rapid bolus immediately followed by 20 mL saline flush 2, 3
• If no conversion within 1-2 minutes: 12 mg IV push 2, 3
• If still no conversion: second 12 mg dose (maximum total 30 mg) 2, 3

Success rates: 69-95% for terminating AVNRT and AVRT 1, 4, 5, 6

Critical Safety Considerations

Must Have Available

• Defibrillator must be immediately available when administering adenosine, especially if Wolff-Parkinson-White syndrome is possible 2
• Continuous ECG monitoring during administration 2

Dose Modifications Required

• Reduce to 3 mg initial dose for patients taking dipyridamole or carbamazepine, transplanted hearts, or central venous access 2, 3
• Increase dose for patients on theophylline, caffeine, or theobromine 2, 3

Absolute Contraindications

• Asthma or bronchospastic lung disease (risk of severe bronchospasm) 2, 3
• Second- or third-degree AV block without pacemaker 3
• Sick sinus syndrome without pacemaker 3
• Known hypersensitivity to adenosine 3

Alternative Injectable Options (If Adenosine Fails or Contraindicated)

Second-Line Agents for Hemodynamically Stable Patients

IV calcium channel blockers (Class IIa recommendation):

• Diltiazem or verapamil can be effective for acute SVT treatment 1
• Conversion rates: 64-98% 1
• Slow infusion over 20 minutes reduces hypotension risk 1
• Do NOT use if:
  • Suspected ventricular tachycardia 1
  • Pre-excited atrial fibrillation (can cause ventricular fibrillation) 1
  • Systolic heart failure 1

IV beta blockers (Class IIa recommendation):

• Reasonable alternative for hemodynamically stable SVT 1
• Excellent safety profile but less effective than calcium channel blockers 1

Common Pitfalls to Avoid

Administration Errors

• Slow push renders adenosine ineffective - must be rapid bolus 2, 3
• Inadequate saline flush - must use 20 mL immediately after 2, 3
• Peripheral IV too distal - use large proximal vein 2

Rhythm Misidentification

• Adenosine given for non-SVT rhythms (sinus tachycardia, atrial fibrillation, wide-complex tachycardia) will not convert but is generally safe 7, 5
• If wide-complex tachycardia, assume ventricular tachycardia unless proven otherwise 1
• Adenosine can be used diagnostically for stable wide-complex tachycardia (Class IIb) but only if regular and monomorphic 1

Drug Interactions

• Verapamil should never be given after beta blockers (risk of profound bradycardia and hypotension) 1
• Methylxanthines (theophylline, caffeine) reduce adenosine effectiveness 3
• Dipyridamole potentiates adenosine effect 3

Expected Side Effects (Transient, <60 seconds)

• Flushing, dyspnea, chest discomfort (most common, >10% incidence) 3, 4
• Headache, throat/neck/jaw discomfort 3
• All effects resolve within seconds due to 0.6-10 second half-life 4

Post-Conversion Management

• Monitor for recurrence after successful conversion 2
• Recurrence occurs in approximately 15-20% of patients 7
• If recurs: repeat adenosine or consider longer-acting AV nodal blocker (diltiazem or beta-blocker) 2

Special Population: Pregnancy

• Adenosine is safe and effective during pregnancy 2