When should adenosine be administered to a patient with supraventricular tachycardia (SVT) or other arrhythmias, considering their medical history, including conditions like asthma or chronic obstructive pulmonary disease (COPD)?

When to Give Adenosine

Adenosine should be administered for hemodynamically stable patients with regular narrow-complex supraventricular tachycardia (SVT) after vagal maneuvers fail, but must be avoided in patients with asthma or other bronchospastic lung disease due to risk of severe bronchospasm. 1, 2

Primary Indications

Adenosine is the drug of choice for terminating SVT involving the AV node in the reentrant circuit, including:

• AV nodal reentrant tachycardia (AVNRT) - terminates approximately 95% of cases 1
• AV reciprocating tachycardia (AVRT) - success rates of 78-96% 1
• Paroxysmal supraventricular tachycardia (PSVT) - overall success rate of 93% across clinical trials 3

The American Heart Association recommends vagal maneuvers as first-line intervention, with adenosine as the next step if these fail 1. For hemodynamically unstable patients, synchronized cardioversion takes priority, though adenosine may be considered first if the tachycardia is regular with narrow QRS complex 1.

Absolute Contraindications

Do not administer adenosine in patients with:

• Asthma or bronchospastic/bronchoconstrictive lung disease - can cause severe, potentially life-threatening bronchospasm 1, 2
• Second- or third-degree AV block (unless functioning pacemaker present) 2
• Sick sinus syndrome or symptomatic bradycardia (unless functioning pacemaker present) 2
• Known hypersensitivity to adenosine 2

Critical Safety Considerations

A defibrillator must be immediately available when administering adenosine, particularly in patients where Wolff-Parkinson-White (WPW) syndrome is a consideration, as adenosine can precipitate atrial fibrillation with rapid ventricular rates or even ventricular fibrillation 1, 4. This is especially critical in wide-complex tachycardias of uncertain etiology 4.

Use with extreme caution or avoid in:

• Patients with acute myocardial ischemia or unstable angina - fatal cardiac events including cardiac arrest, sustained ventricular tachycardia, and myocardial infarction have occurred 2
• Obstructive lung disease without bronchospasm (emphysema, bronchitis) - use cautiously with close monitoring 2
• Pre-existing first-degree AV block or bundle branch block - monitor closely for progression 2

Diagnostic Applications

Adenosine serves dual therapeutic and diagnostic purposes:

• Unmasks underlying atrial flutter or atrial tachycardia by causing transient AV block while revealing persistent atrial activity 1, 5
• Helps differentiate wide-complex tachycardias - can distinguish supraventricular from ventricular origins 5
• Distinguishes atrial fibrillation from regular SVT by temporarily slowing ventricular rate and revealing irregular atrial rhythm 4

However, adenosine carries a 12% risk of worsening atrial fibrillation and should be used cautiously in this context 4.

Dosing Protocol

Standard peripheral IV administration:

• Initial dose: 6 mg rapid IV push through a large proximal vein, followed immediately by 20 mL saline flush 1, 5
• If no conversion within 1-2 minutes: 12 mg IV push 1, 5
• May repeat 12 mg dose once more if needed 1

Dose modifications required:

• Reduce initial dose to 3 mg for patients taking dipyridamole or carbamazepine, those with transplanted hearts, or when giving via central venous access 1, 6
• Increase doses may be needed in patients with significant blood levels of theophylline, caffeine, or theobromine 1, 5

Central venous administration requires lower doses (start with 3 mg) as 77% of episodes terminate with this dose centrally versus only 37% peripherally 6.

Special Populations

Pregnancy: Adenosine is safe and effective during pregnancy according to the American Heart Association 1.

Common Pitfalls to Avoid

• Failing to have resuscitative equipment available - this is mandatory given risks of cardiac arrest, severe bronchospasm, and ventricular arrhythmias 2
• Using in patients with unrecognized WPW syndrome and atrial fibrillation - can precipitate ventricular fibrillation requiring immediate defibrillation 4
• Not monitoring for immediate recurrence - patients commonly experience premature complexes post-conversion that trigger recurrent SVT within seconds to minutes 1
• Forgetting to adjust dose for drug interactions - dipyridamole enhances adenosine's effect while methylxanthines reduce it 5, 2

Post-Conversion Management

Continuous cardiac monitoring is essential immediately after conversion as recurrence is common 1. If immediate reinitiation occurs, consider prophylactic AV nodal blockade with longer-acting agents such as diltiazem or beta-blockers 1. If adenosine reveals atrial flutter or other non-AV nodal dependent arrhythmias, transition to appropriate longer-acting AV nodal blocking agents for sustained rate control 1, 5.