question about adenosine in SVT

[traitorman]

correct me if I'm wrong but SVT IS AVRT/AVNRT. WPW is a type of AVRT. you don't want to block the AV node in WPW because you don't want to force all the signals through the accessory pathway. well if SVT can technically be due to an accessory pathway, why can you give adenosine in SVT but not in WPW?

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[CliveStaples]

AVNRT (SVT) is different from AVRT (WPW would be an example). SVT is caused by a functional re-entry whereas WPW is caused by an anatomical anomaly which causes re-entry. A functional cause can safely be fixed with a "hard reset" as opposed to an anatomical cause.

 

[e30ftw]

Adenosine will treat orthodromic tachycardia in WPW syndrome.

Adenosine may cause deterioration of the underlying rhythm to V-tach/fib/torsades if given to treat an antidromic WPW arrhythmia (classically afib). For this reason I keep pads attached and a lifepak handy during chemical cardioversion.

Also antidromic wpw is usually wide complex and looks bad from across the room. In general adenosine should be avoided in patients with wide complex arrhythmias, especially if irregular; instead consider procainamide or cardioversion..

 

[da8s0859q]

In general adenosine should be avoided in patients with wide complex arrhythmias, especially if irregular; instead consider procainamide or cardioversion..

This right here.

 

[nlax30]

Adenosine will affect conduction at the AV node, so in theory any reentrant arrhythmia which involves the AV node in it's circuit could be terminated with adenosine. AVNRT is a reentrant circuit within the AV node itself (involving the fast and slow pathyways) so adenosine would work. AVRT, whether antidromic or orthodromic is a larger reentrant arrhythmia making use of a bypass tract as well as the AV node as part of the circuit so blocking any part of that circuit would terminate it.

The specific instance in someone with WPW where you would NOT want to use adenosine is during afib/aflutter. In those arrhythmias the arrhythmia focus is either from multiple randomly firing foci in the atria (afib) or a reentrant circuit in the right atrium (classic right sided aflutter) neither of which make use of the AV node as part of the arrhythmia, so you could block the AV node but the arrhythmia continues to go on and now bombard the bypass tract potentially exposing the ventricle to these rhythms.

Even in a REGULAR wide complex tachycardia adenosine should be safe to use, if it's VT it probably won't do much anyway (though there are some VT-senstive VTs...) and won't hurt.

Couple links to look at:
http://hqmeded-ecg.blogspot.com/2011/05/wide-complex-tachycardias-2-cases-what.html

http://lifeinthefastlane.com/ecg-library/pre-excitation-syndromes/

 

[traitorman]

awesome stuff guys, this cleared it up for me. thanks!

 

[tux4]

Also just wanted to add something on the side because I have seen people confuse this. SVT is not a specific diagnosis, but just an EKG description. It is general term saying the problem is above the ventricles. Sinus tachy, multifocal atrial tachy, AVRT, AVNRT, afib, and a flutter are all SVT.


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[The White Coat Investor]

While we're on the subject, let me throw out a pearl.

If you ever have to give adenosine through a central line, don't give the full 6 mg dose. It makes for a really, really long pause. 2 mg is probably plenty. There is much less degradation of the adenosine between the SVC and the heart than between the AC and the heart. Makes sense, but if you don't think about it, you'll make the same mistake.

 

[engineeredout]

While we're on the subject, let me throw out a pearl.

If you ever have to give adenosine through a central line, don't give the full 6 mg dose. It makes for a really, really long pause. 2 mg is probably plenty. There is much less degradation of the adenosine between the SVC and the heart than between the AC and the heart. Makes sense, but if you don't think about it, you'll make the same mistake.

Also heart transplant patients, because they are denenervated, get half dose adenosine as well