Differentiating AVNRT from really regular Af + use of adenosine

[BushyFromOz]

HI kids

topic title is pretty much the question.

up until recently, our IC's used verapamil for SVT within some pretty strict criteria, then adenosine was introduced (in a very poor fasion may i add) and the controls around managing SVT's relaxed. So basically these patient are being managed a heck of a lot more than we used to. Because of this historical context, the experience in managing AVNRT and AVRT's is at the moment quite poor, and creates some hesitation when you get to the connundrum of is this SVT or is this really regular Atrial fib.

Reason i ask is i had a patient the other day with a HR of 202, no discernable P waves at all in Ld2, and when you mapped out the R-R intervals on a strip they were predominantly regular but occasionally had periods of slight irregularity. The monitored rate was also slightly variable at times in that it would run at 202 for 20 seconds, then 198 for half a minute in that sort of fashion.

On moving this guy to the stretcher before chemical reversion his rate dropped to 150 where it fluctuated +/- 6 beats per minute, so the decision was made to not chemically revert.

My question is, if you are unable to diferentiate between atrial fib and SVT, and you choose to give adenosine, is "paying off" as SVT, particulalry when symptomatic a sound clinical choice, or is erring on the side of it being Atrial Fib a better option? And if you give adenosine to atrial fib, are there increased risks involved.

Posted from a mobile phone so i have no resources to look at this myself for a few more hours

[scubanurse]

From my understanding of A-fib with RVR is that if it has been chronic, converting it in the field can lead to more complications. I have seen several AFRVR cases where they tach along in the 130-170's and the doctors are so so hesitant to treat it because of the increased risk of thromboembolism. I'm too tired right now to do much research, but I believe if it is unclear then err on a-fib until at the ER or if you can have the doc look at the strip and decide, even better.

[BushyFromOz]

3 days and only 106 views and 1 comment? Boy, this place has really slowed down over the last few years....

[paramedicmike]

Adenosine isn't going to convert an AFib so I don't know that I would worry too much about giving it to someone if that's what you suspect. You may see a "transient or modest slowing" after you give it. But it won't convert them. As such, I've heard it recommended that if you're unsure if it's SVT or Afib a trial of adenosine can be used. If it works it's an SVT. If it doesn't it's afib.

Of course, if they're *that* unstable then cardioversion would bypass the chemical conversion trials.

Be wary, though. Sometimes chemical conversion of an SVT with adenosine can result in a transient Afib. So if you give adenosine and it breaks the tachycardia, don't be fooled into thinking it was an underlying afib that caused the problem.

Does this help?

[BushyFromOz]

Thanks mike

This issue for us i guess is the "is it AVNRT or Af" when your looking at rates in excess of 200 and the rate is regular but not metronomically regular (as in the rate will have slight variation over a period of time, say a minute) as a true AV nodal re entrant should be, and i cant see any reason why you would not manage them as SVT as the insanely short half life makes it relatively safe if it is in fact atrial fib. Indeed i have seen several time in hospital of patients who are unsuccessfully beta blocked given adenosine as an almost diagnostic test of sorts.

But for us atrial fib is an absolute contraindication for adenosine, and i cant seem to find any supporting evidence of that, so the issue of is this SVT or really fast and regular atrial fib that much more of an issue for us.

[Richard B the EMT]

It may be slow, due to it being a weekend. This is beyond my scope of practice, anyway, but I'm going to learn something from the paramedics, anyway.

[MariB]

It may be slow, due to it being a weekend. This is beyond my scope of practice, anyway, but I'm going to learn something from the paramedics, anyway.

I don't have any pop corn, would you like a pop tart?

I read these too, usually very confused but hope I will learn something

[Eydawn]

Man, cardiac really isn't my thing just yet... if the half life is short and there's no reasons that you can find for contraindication, I might be getting ahold of whoever does your protocols to see WHY it's an absolute contra for you...

Don't have much to offer on the pharma/physio side of things for this one, sorry!

Wendy

CO EMT-B

RN-ADN

[fakingpatience]

Our protocols specifically said that if you aren't certain if it is SVT or other rapid atrial rhythm to give a trial dose of 6mg adenosine, to slow the rhythm down for diagnostic purposes. Personally the a-fib RVR pt's I've had have been fairly irregular rates, so it wasn't needed, however I did have a pt in a regular a-flutter (1:1 conduction) undecernable to SVT at the rate. Gave 6mg of adenosine, and the rhythm slowed for ~10 seconds, long enough to see the flutter waves and determine a calcium channel blocker was needed (didn't carry cardizem there so opted to not treat and wait till we reached the ER as pt was stable).

[HarryM]

Hmmm I'm not sure on that one. We use adenosine ONLY for SVT. You have to be 100% certain it is SVT. Otherwise for all other compromised tachydysrythmia's it's an amiodarone infusion and/or electric cardioversion for significant compromise. I'd be pretty wary of making a guess with any cardiac drug, but adenosine can be pretty nasty so personally I'd err on the side of caution and not go down that line unless certain it was SVT or consulted with clinical and got their view on the rhythm.