Cardiology - AVNRT vs A-Tach

[Sugi]

So I was in my cardiology class, and I had a question for my teacher that I just am not sure I got the best answer for...

Looking at an EKG strip, with no patient history, how can you differentiate between an AVNRT and Atrial Tachycardia?

The answer I received was that you would need a patients history to tell, because really the only way to tell is to treat an AVNRT as if it was A-tach and the patient gets worse.

 

[bmc911]

this is my understanding of it after doing some research in regards to this

AVNRT and A-tach are going to be treated exactly the same and the treatment for both will either work or not. the only difference between the two is where the reentrant originates. on an ECG i dont believe youll be able to differentiate.

now WPW(wolf parkinson white syndrome) is a whole nother ball of wax. this is the patient that will present with a-tach or SVT looking ECG but THIS treatment will make an otherwise basic cardiac call go south. to differentiate, your WPW will have a very short PR interval, QRS >120MS, and a Delta wave in the R wave or slurring of the R wave. im thinking this is what your instructor might have been referring to.

im new here so i think ive attatched a WPW with the delta waves circled in red

 

[bmc911]

YAH!!! i did it, cool.

hope that pic is big enough and here is a link with info on AVNRT/a-tach

http://emedicine.medscape.com/article/160215-overview

 

[boingo]

this is my understanding of it after doing some research in regards to this

AVNRT and A-tach are going to be treated exactly the same and the treatment for both will either work or not. the only difference between the two is where the reentrant originates. on an ECG i dont believe youll be able to differentiate.

now WPW(wolf parkinson white syndrome) is a whole nother ball of wax. this is the patient that will present with a-tach or SVT looking ECG but THIS treatment will make an otherwise basic cardiac call go south. to differentiate, your WPW will have a very short PR interval, QRS >120MS, and a Delta wave in the R wave or slurring of the R wave. im thinking this is what your instructor might have been referring to.

im new here so i think ive attatched a WPW with the delta waves circled in red

The treatment of narrow complex SVT in the setting of WPW is no different, Adenosine is the drug of choice, the trouble you get in is when AF or wide complex rhythms are present. Orthodromic SVT is narrow, and unless the patient knows they have a hx of WPW, you are unlikely to pick it up until the rhythm has converted to NSR. It is quite difficult to appreciate a delta wave in a narrow complex tach at 200.

 

[TomB]

To add to what boingo said, with orthodromic AVRT in the presence of WPW, the circus movement tachycardia goes down the AV node and up the accessory pathway, so you won't see delta waves during the tachycardia. You'll see them after the conversion.

I don't like the term SVT or "atrial tachycardia" because they mean almost nothing. You might as well substitute the phrase "non-ventricular tachycardia". For some reason a lot of paramedics think SVT is the name of a specific arrhythmia, but it's not. Technically "atrial tachycardia" does not require the AV node for its maintenance, but so what?

I prefer the terms "narrow complex tachycardia" and "wide complex tachycardia" because almost everyone understands that "narrow complex tachycardia" is a classification of tachycardias that includes sinus tachycardia, atrial fibrillation with ventricular rate > 100, atrial flutter with ventricular rate > 100, and the reentrant arrhythmias, including those involving an accessory pathway.

Tom

 

[bmc911]

to get back to Sugi's question, these are the tell tale AVNRT signs. when referring to abrupt below, i think this refers to without medical intervention causing rythym termination

The onset is abrupt with an atrial premature complex, which conducts with a prolonged PR interval.
The PR interval may shorten over the first few beats at onset, or it may lengthen during last few beats preceding termination of the tachycardia.
Abrupt termination occurs with a retrograde P wave, sometimes followed by a brief period of asystole or bradycardia


as far as WPW, in many cases you will see 2 of the 3 criteria: QRS greater than 120ms and a delta wave. more than likely you will not see the P or a short PR cause it will be buried in the preceeding complex. emergency treatment is controversial as far meds go, at least from what im finding now and what i was taught. whether you know, suspect or dont know if its WPW just keep in mind the normal adenosine or calcium channel blocker can possiblly cause v-tach or v-fib. v-fib is usually associated with a rapid a-fib and underlying WPW.

as with any cardiac med, just be prepared mentally for other arrythmias and associated effects

 

[bmc911]

one more AVNRT ECG thing. i was just BSin about this with an OG medic and he was sayin the other thing that will differ from an a-tach is the QRS will be wider than .12 but not wider than .16ms depending on where in the AV reentrant phenom is.

 

[TomB]

Your friend sounds confused. AVNRT does not generally present as a wide complex rhythm unless there is a pre-existing bundle branch block or there is some kind of rate-related aberrancy.

It's always nice if you have the luxury to see the onset or termination of a narrow complex tachycardia (as you suggest a paroxysmal onset favors a reentrant mechanism) but we're rarely that fortunate in the field.

It's a lot easier to document that sort of thing in the inhospital setting.

Tom