What is the role of adenosine in treating different types of arrhythmias, including supraventricular tachycardia (SVT), atrial fibrillation, and ventricular tachycardia?

Adenosine in Different Types of Arrhythmias

Direct Answer

Adenosine is the drug of choice for terminating supraventricular tachycardias (SVT) that involve the AV node in the reentrant circuit, with success rates of 78-96%, but it has no role in terminating atrial fibrillation, atrial flutter, or ventricular tachycardia—though it serves valuable diagnostic purposes in these latter arrhythmias. 1, 2

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Role by Arrhythmia Type

Supraventricular Tachycardia (SVT)

Therapeutic Indication:

• Adenosine is the first-line pharmacological agent for terminating AV nodal re-entrant tachycardia (AVNRT) and AV re-entrant tachycardia (AVRT), with success rates of 78-96% and specifically 95% for AVNRT. 1, 2
• It works by selectively blocking AV nodal conduction through A1 receptor activation, which produces negative chronotropic and dromotropic effects. 2
• Adenosine should only be used after vagal maneuvers fail in hemodynamically stable patients with regular narrow-complex SVT. 1

Administration Protocol:

• Initial dose: 6 mg IV push via large proximal vein, followed immediately by 20 mL saline flush. 1
• If no conversion within 1-2 minutes: administer 12 mg IV push. 1
• If still no response: may give one additional 12 mg dose. 1
• The entire effect occurs within 30 seconds of administration due to the extremely short half-life of less than 10 seconds. 3, 4

Atrial Fibrillation and Atrial Flutter

No Therapeutic Role:

• Adenosine does not terminate atrial fibrillation or atrial flutter. 2
• It transiently slows the ventricular rate by blocking AV nodal conduction, but the underlying atrial arrhythmia persists. 2

Diagnostic Value:

• Adenosine can unmask atrial flutter or atrial tachycardia by temporarily slowing AV conduction, allowing visualization of flutter waves or P waves on ECG. 1, 2
• Continuous ECG recording during administration is essential to capture this diagnostic information. 1, 2

Ventricular Tachycardia (VT)

No Therapeutic Effect:

• Adenosine has no effect on ventricular tachycardia because VT does not involve the AV node in its circuit. 3, 4

Critical Diagnostic Application:

• In patients with wide-complex tachycardia of uncertain etiology, adenosine helps differentiate SVT with aberrancy from VT. 3, 2
• If the tachycardia terminates, it was likely SVT; if no effect occurs, VT is more probable. 3
• This diagnostic maneuver must be performed in a monitored environment with resuscitation equipment immediately available. 3, 5

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Critical Safety Considerations

Absolute Contraindications:

• Asthma or bronchospastic lung disease: Risk of severe bronchospasm. 3, 1, 2
• Second- or third-degree AV block or sick sinus syndrome (unless pacemaker present). 2

High-Risk Situations Requiring Extreme Caution:

Wolff-Parkinson-White (WPW) Syndrome:

• Adenosine can precipitate atrial fibrillation with rapid ventricular rates via the accessory pathway, potentially degenerating to ventricular fibrillation. 3, 1, 6
• A defibrillator must be immediately available when administering adenosine if WPW is suspected. 1
• Three cases of adenosine-induced atrial pro-arrhythmia (atrial fibrillation and flutter) have been documented in children with WPW. 6
• One case report documented ventricular fibrillation induction in a patient with rapidly conducted atrial fibrillation, even without demonstrable accessory pathway. 5

Dose Modifications Required:

Reduce initial dose to 3 mg in:

• Patients taking dipyridamole (enhances adenosine effect). 3, 1, 2
• Patients taking carbamazepine. 1, 2
• Heart transplant recipients (denervated hearts are hypersensitive). 1, 2
• Administration via central venous access. 1, 2

Increase dose requirements in:

• Patients with significant theophylline, caffeine, or theobromine levels (competitive antagonism at adenosine receptors). 1, 2

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Common Side Effects and Management

Expected Transient Effects (lasting <60 seconds):

• Flushing, dyspnea, and chest discomfort are the most common side effects. 3, 1, 2
• Headache, throat/neck/jaw discomfort, and dizziness may occur. 2
• Transient complete heart block can occur—adenosine must be given in a monitored environment with resuscitation equipment available. 3, 5

Rare but Serious Pro-arrhythmic Events:

• Atrial fibrillation induction (especially in WPW). 6
• Ventricular fibrillation (extremely rare, even in structurally normal hearts). 5
• These risks mandate that prompt access to defibrillation and transcutaneous pacing be available with every administration. 5

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Special Populations

Pregnancy:

• Adenosine is safe and effective during pregnancy. 1

Pediatric Patients:

• Adenosine is superior to lanatoside C in children for terminating PSVT. 4
• The same pro-arrhythmic risks apply, including atrial fibrillation induction in children with WPW. 6

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Post-Conversion Management

• Monitor for immediate recurrence after successful conversion. 1
• If recurrence occurs, re-administer adenosine or transition to a longer-acting AV nodal blocking agent (diltiazem or β-blocker). 1
• If adenosine unmasks another form of SVT (atrial flutter, atrial tachycardia), treat with appropriate longer-acting agents rather than repeat adenosine. 1