2nd Degree AV Block, Type I

Otherwise known as Wenckebach, or perhaps my favorite of the AV Blocks.  It has a certain je-nes-sais-quoi to it.  It is dynamic, but rather non-threatening.

wenckebach1

The classic definition of 2nd Degree AV Block, Type I, is an increasing PR interval until a QRS complex is dropped.  “Longer, longer, drop, you’ve got yourself a Wenckebach” is a nice little mnemonic to remember when determining the rhythm.  Starting from the 4th beat in on the strip, you can see the PR interval goes from .24s, .26s, then .36s and a complex is dropped in the next round.  But you ask, where is the P wave for the dropped complex?  It’s buried in the T-wave from beat #6.  One other identifying feature of Wenckebach is that the P-P interval remains constant, in this case .64s, and the R-R interval lengthens as well.

Normally, this is a problem with the AV node, although there are some occasions where it occurs below the node, in the His-Perkinje fibers.  Occasionally you will get wide and bizarre QRS complexes with both above and below the node eitilogies, but more commonly narrow complex QRSs will be the norm.

Causes can include drug induced, from beta and calcium channel blockers, digoxin and amiodarone, also in cases of acute myocardial infarction (most commonly inferior wall).  Unlike Type II block which can evolve into 3rd degree block, Type I does not evolve into anything worse on its own.  Patients are rarely symptomatic just from the rhythm, and symptoms are usually a result of the precipitating factors. Unlike 3rd degree block, there is not much for us nurses to do except to monitor the patient.  As these folks are usually asymptomatic, it’s all we can do.  Past that, if symptoms are present, we can treat the symptoms.

And just because we’re talking Wenckebach, I have to include the classic YouTube gem:

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