Know Before You Push -- Adenosine

This is the first in a series of articles focusing on important pharmacologic agents used in emergency medicine.  Key principles of dosing, administration, efficacy are reviewed in an evidenced based format.  Special attention is also given to the rare, uncommon, and/or under-appreciated effects of these medications.

Optimizing Vagal Maneuvers

Vagal maneuvers are recommended as an initial treatment of SVT, especially after immediate onset of tachycardia.  In a 1988 Lancet paper, vagal maneuvers were tested in 35 patients with SVT, with each maneuver used up to three times in an attempt to terminate tachycardia.  The Valsalva maneuver in the supine position was most effective, terminating SVT in 54% of cases.  Right carotid massage was only effective in 17% of cases, left carotid massage in 5% of cases, and the diving reflex in 17% of cases.  

Adenosine or CCB

When SVT is treated pharmacologically, adenosine and calcium channel blockers are frequently utilized to slow conduction for rate control and rhythm identification.  

A 2009 Cochrane Review found no significant difference in reversion or relapse rate betweenIV calcium channel blockers (CCB) and adenosine in the treatment of SVT. 

Time to reversion to sinus rhythm for verapamil was noted to be slower than adenosine in all studies reviewed.  Hypotension associated with verapamil use was more likely to be seen as a major adverse effect. However, side effects including nausea, chest tightness, dyspnea, and headache were more frequent with adenosine (10.8%) when compared with verapamil (0.6%).

Proarrhythmic Effects

Although widely used and generally safe, arrhythmias associated with the administration of adenosine have been well described.  Mallet reviewed the literature on the proarrhythmic effects of adenosine in 2004.  He noted that severe bradycardias and tachyarrhythmias induced by adenosine had been reported in over a decade of literature.

Enhanced effects of adenosine can be seen in the elderly, patients with sinus node dysfunction, patients taking dipyridamole, carbamazepine, digoxin, verapamil, and beta blockers.

Reduced efficacy of adenosine can be seen in patient taking theophylline and caffeine. Patients with a history of recurrent palpitations (suggesting possibility of latent pre-excitation or dual AV node physiology) should be monitored for the  induction of unstable tachydysrhythmias.

Dosing Considerations

Cairns et al. reported in 1991 that using an initial 12mg dose of IV adenosine increases the likelihood of conversion with a single dose without additional harm.  In contradistinction, dosing of adenosine should also be lowered in cardiac transplant patients to 1-3 mg IV, as these patients are particularly sensitive to adenosine.

-- Eric Beck, DO, EMT-P

References:

Mehta D, et al.  “Relative Efficacy of Various Physicial Manoeuvres in the Termination of Junctional Tachycardia.” The Lancet, May 28, 1988, 1181-1185.

Cairns C, et al. “Intavenous Adenosine in the Emergency Department Mangement of Paroxysmal Supraventricular Tachycardia.” Annals of Emergency Medicine. 1991;20:7, 717-721.

Mallet M.  “Proarrhythmic effects of adenosine: a review of the literature.” Emerg Med J. 2004;21:408-410.

Holdgate A, Foo A.  “Adenosine versus intravenous calcium channel antagonists for the treatment of supraventricular tachycardia in adults (Review).”  The Cochrane Library. 2009:1.