Adenosine (Adenocor)

This endogenous nucleoside is safe and effective in ending > 90% of re-entrant paroxysmal SVT.However, this is not the most common type of SVT in the critically ill patient.After an IV bolus effects are immediate (10–30 seconds), dose-related and transient (half-life <10 s; entirely eliminated from plasma in <1 minute, being degraded by vascular endothelium and erythrocytes). Its elimination is not affected by renal/hepatic disease. Adenosine works faster and is superior to verapamil. It may be used in cardiac failure, in hypotension and with B-blockers, in all of which verapamil is contraindicated.

Uses:
It has both therapeutic and diagnostic uses:
• Alternative to DC cardioversion in terminating paroxysmal SVT, including those associated with WPW syndrome
• Determining the origin of broad complex tachycardia; SVT responds, VT does not (predictive accuracy 92%; partly because VT may occasionally respond).Though adenosine does no harm in VT, verapamil may produce hypotension or cardiac arrest

Contraindications:
Second- or third-degree heart block (unless pacemaker fitted)
Sick sinus syndrome (unless pacemaker fitted)
Asthmatic – may cause bronchospasm
Patients on dipyridamole (drastically prolongs the half-life and enhances
the effects of adenosine – may lead to dangerously prolonged highdegree AV block)

Administration:
• Rapid IV bolus: 3mg over 1–2 seconds into a large vein, followed by rapid flushing with sodium chloride 0.9%
If no effect within 2 min, give 6mg
If no effect within 2 min, give 12mg
If no effect, abandon adenosine
Need continuous ECG monitoring
More effective given via a central vein or into right atrium

How not to use adenosine:
Without continuous ECG monitor

Adverse effects:
Flushing (18%), dyspnoea (12%) and chest discomfort are the commonest side-effects but are well tolerated and invariably last <1min. If given to an asthmatic and bronchospasm occurs, this may last up to 30 min (use aminophylline to reverse).

Cautions:
AF or atrial flutter with accessory pathway (up conduction down anomalous pathway may increase) Early relapse of paroxysmal SVT is more common than with verapamil but usually responds to further doses Adenosine’s effect is enhanced and extended by dipyridamole – if essential to give with dipyridamole, reduce initial dose to 0.5–1mg