What is the role of adenosine in treating supraventricular tachycardia (SVT)?

Role of Adenosine in Treating Supraventricular Tachycardia (SVT)

Adenosine is recommended as a first-line pharmacological treatment for regular SVT after vagal maneuvers, with success rates of 78-96% in terminating AVNRT and AVRT, and serves an important diagnostic role in unmasking other atrial arrhythmias. 1

Treatment Algorithm for SVT

Initial Assessment and Management

• For hemodynamically stable patients with regular SVT, begin with vagal maneuvers (Valsalva, carotid sinus massage) in the supine position as first-line intervention 1
• If vagal maneuvers fail, adenosine is the recommended next step for acute treatment of regular SVT 1
• For hemodynamically unstable SVT with hypotension, altered mental status, shock, chest pain, or heart failure symptoms, synchronized cardioversion is indicated, though adenosine should be considered first if the tachycardia is regular with narrow QRS complex 1

Adenosine Administration

• Administer via proximal IV as a rapid bolus followed by saline flush 1
• Initial dose of 6 mg IV push, followed by up to two additional 12 mg boluses if necessary at 1-2 minute intervals 1
• Continuous ECG recording during administration helps diagnostically and distinguishes between drug failure and successful termination with immediate reinitiation 1
• The single-syringe technique may be as effective as the traditional double-syringe technique, with potentially higher first-dose termination rates 2

Mechanism and Effectiveness

• Adenosine exerts a direct depressant effect on SA and AV nodes through activation of purine receptors (A1 and A2), causing transient AV nodal block 3
• Highly effective in terminating SVTs that involve the AV node in the reentrant circuit (AVNRT and AVRT) with success rates of 78-96% 1
• Adenosine terminates approximately 95% of AVNRT cases 1
• Recent data shows an overall response rate of 86% in patients with paroxysmal SVT 4
• Older age and history of previous SVT episodes are associated with increased likelihood of successful conversion 4

Diagnostic Value

• Serves as both therapeutic and diagnostic agent for narrow-complex tachyarrhythmias 1
• Can unmask atrial flutter or atrial tachycardia, though it rarely terminates these arrhythmias 1
• Helps distinguish between different types of SVT based on response pattern 1

Safety Profile and Precautions

• Very short half-life (less than 10 seconds) makes serious adverse effects rare 3, 1
• Common side effects include chest discomfort, shortness of breath, flushing, and headache, but these are transient 1, 5
• Use with caution in patients with:
  • Pre-existing first-degree AV block or bundle branch block 3
  • Obstructive lung disease not associated with bronchoconstriction 3
  • Autonomic dysfunction, hypovolemia, stenotic valvular heart disease 3
• Contraindicated in:
  • High-grade AV block or sinus node dysfunction (except with functioning pacemaker) 3
  • Bronchoconstriction or bronchospasm (e.g., asthma) 3
  • Unstable angina or acute myocardial ischemia 3

When Adenosine Fails

• If adenosine fails to terminate SVT, consider:
  • Synchronized cardioversion for hemodynamically unstable patients 1
  • Intravenous beta blockers, diltiazem, or verapamil for hemodynamically stable patients 1
• Arrhythmias may recur within minutes in a minority of patients after successful conversion 6
• Adenosine will not terminate atrial flutter or intra-atrial reentry but will produce transient AV block during these arrhythmias 7

Special Considerations

• Adenosine is safe and effective in pregnancy 1
• Larger doses may be required for patients with significant blood levels of theophylline, caffeine, or theobromine 1
• Initial dose should be reduced to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access 1
• Avoid in patients with asthma due to risk of bronchospasm 1, 3