Pediatric emergency medicine trisk 1725 1725
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to record a rhythm strip during adenosine administration as well as during vagal
maneuvers. Once adenosine has been administered, assess the EKG for adequate
response of AV or VA dissociation from the adenosine. Note signs of AV
dissociation, tachycardia termination, slowing, or irregularity of the rhythm. The
mechanism of tachycardia is often revealed with initiation or termination of the
rhythm.
Administration of adenosine will result in one of three possible outcomes: It
may have no effect on the rhythm; it may terminate tachycardia resulting in sinus
rhythm; or it may reveal atrial flutter waves or atrial tachycardia during transient
blocking of the AV node. Tachycardia will resume after adenosine is metabolized
( Fig. 86.1 ).
In the first case, when adenosine has no effect on the rhythm, it is either
because the dose was too low, it was metabolized before it reached the heart, or
the rhythm is VT. The dose should be doubled and properly administered. The
higher dose may be given twice. If the rhythm is determined to be VT, follow the
management of wide complex arrhythmias below.
In the second case, when adenosine successfully terminates tachycardia, next
steps include recording the EKG in sinus rhythm and monitoring on telemetry
until admission, transfer, or cardiology consultation. If adenosine is successful in
terminating tachycardia but it recurs, adenosine may be given again. Another
option is to administer a longer-acting drug and then repeat conversion with
adenosine.
The third case is when adenosine administration reveals atrial flutter or atrial
tachycardia. One common pitfall is the assumption that the tachycardia briefly
stopped and then restarted in response to adenosine, when in reality adenosine
simply unmasked the rhythm by blocking AV conduction to the ventricles, thus
making the atrial flutter waves obvious. To avoid this pitfall, look for flutter
waves or atrial tachycardia P waves during the time of slowing/AV node
inhibition ( Figs. 86.2 –86.5 ).
If adenosine successfully converts SVT to sinus rhythm, but the tachycardia
recurs, electrical cardioversion offers no advantage over redosing adenosine. In
this case, a longer-acting medication is needed. If the patient is on chronic
antiarrhythmic therapy, consider giving this medication. Useful IV medications
include procainamide, esmolol, or amiodarone. Oral beta-blockers, sotalol, or
flecainide may be used. Calcium channel blockers should not be used in patients
less than 2 years of age, in combination with beta-blockers, or with poor
ventricular function. Cardiology consultation is advised. If adenosine fails to
convert tachycardia at all, electrical cardioversion is indicated.
