Cardiac rhythm confusion

[EMT-IT753]

A co-worker of mine tossed a rhythm strip at me the other day and gave me the, "What is it?" drill that I get quite often as a parapup student.

I do not have the strip on me but I can describe it:
Third degree block with narrow QRS complexes and a rate of 84.

I am trying to understand how this works. To me, a complete block typically has wide QRS complexes and an intrinsic rate of 15-40.

How is this possible?

 

[zmedic]

There could be a block between the SA and AV node, so you get a junctional rhythm that isn't associated with the non-conducted atrial beats.

Hard to be more specific than that without looking at the strip. But if it is narrow complex it has to be coming from above the level of the ventricles.

 

[Scott33]

Its a common misconception that 3rd degree has to have a wide QRS. Look up the difference between intranodal and infranodal AV Blocks.

I would still like to the the strip however

 

[Hellsbells]

The interesting thing about this rhythm is that if it was bradycardic, atropine may be effective.

 

[medicstudent101]

The interesting thing about this rhythm is that if it was bradycardic, atropine may be effective.

I doubt Atropine would be an effective treatment.

 

[usafmedic45]

Depends on the level of the block, but generally it's not going to do much for the ventricular rate.

 

[cwmedic]

Complete block does not always have to be bradycardic, it's only typical. Third degree block is basically a junctional rhythm with atrial beats. This can have an accelerated rates.

No, atropine will not help a dissociated rhythm.

 

[medicstudent101]

Complete block does not always have to be bradycardic, it's only typical. Third degree block is basically a junctional rhythm with atrial beats. This can have an accelerated rates.

No, atropine will not help a dissociated rhythm.

Exactly.

 

[MSDeltaFlt]

Depends on the level of the block, but generally it's not going to do much for the ventricular rate.

Atropine On a complete AVB, can exacerbate the block making it a High Grade Block. You'll be able to see a A-flutter with a ventricular rate somewhere around 15 or so. Atropine is contraindicated for precisely this reason.

 

[18G]

Atropine is not really indicated in a third degree block and is prob not going to increase the ventricular rate much or at all.

Pacing is your first-line intervention with 3rd degree block.

 

[rhan101277]

Yeah, it isn't a problem of to much parasympathetic innervation, its a conduction problem.

Say for example it was a slow 2nd or 3rd degree at 50 and you administered atropine. Well it increases the atrial rate to 80 but has no effect on the ventricular rate, this would make the situation worse. This is why pacing is the first line treatment in this situation.

 

[legion1202]

What bpm are you counting? The strips bpm or what? dont forget that on blocks you need to sometime dig deeper and find the true bpm. 3 degrees are poping p waves normally but the junction isnt listening so its fireing when it thinks it needs to go over.. Giving a you the ekg machine a wrong heart rate.

 

[ArcticKat]

When the P wave is dissociated with the QRS complex we always provide an atrial and a ventricular rate in addition to the actual pulse during report. When providing beats per minute your report should always include the actual perfusing heart rate which should coincide with the QRS complexes.

 

[TomB]

With a complete block, when the atrial rate exceeds the ventricular rate we call it 3AVB. When the ventricular rate exceeds the atrial rate we call it AV dissociation. On rare occasions (for example, acute inferior STEMI with 3AVB and narrow complex escape rhythm where the block is caused by the Bezold-Jarisch reflex -- a state of hypervagotonia) atropine *may* be therapeutic but sometimes it speeds up the atrial rate without speeding up the ventricular rate. You're balancing the problems inherent with shock (supply side ischemia) with the problems inherent with increased heart rate (demand side ischemia). Sometimes it's worth it, sometimes it's not. There are case reports of reduced ST-elevation after atropine indicating that reversing bradycardia and hypotension can be a good thing with acute inferior STEMI. This is an interesting discussion!