okay well welcome to another MedCram lecture we're going to talk about
wolff-parkinson-white syndrome otherwise known as WPW and let's talk about the
conduction system so we can explain what's going on here so here we have the
electrical conduction of the heart and as you know the sinoatrial node is where
the pacemaker usually sits up here and it depolarizes throughout the atrium but
before it goes down to the ventricle all of these pulsations electrical
conduction goes to the AV node which sits right here basically this is the
only pathway for electrical conduction to go down into the ventricles normally
and as you know this is insulated so there's an insulated layer here so that
depolarization of the atria don't go down at all into the ventricle now
that's important because as you know the AV node here only allows a specific rate
of conduction to go through it there's a depolarization and repolarization and
then a refractory period where by which an additional depolarization is not
going to be allowed in straight through and that's kind of a safety mechanism
because as you know an atrial fibrillation up here in the atria the
atria are contracting far more than 400 beats per minute and in that situation
imagine 400 beats per minute being directly transmitted down to the
ventricles I mean that would be fatal so the AV node does serve a very good
purpose in controlling that okay so you know then that there is only one way to
the ventricle well unless unless of course you have
WPW which in this situation you have a congenital abnormality called the bundle
of Kent which basically is a bridge which connects the atria with the
ventricle and so now instead of the electricity the conduction going down
and sweeping in this direction going everything's going to the AV node before
it can go down into the ventricle now you have all of that yes but you can
also take an accessory pathway is called the bundle
of Kent and you can go down into the ventricle directly depending on what
kind of congenital abnormality this is
so you can quickly see here that there's going to be some issues this is still
happening just like it normally does but if this accessory pathway is functional
and it's actually conducting electricity you can see that the first thing that
it's going to do is it's gonna excite the musculature of the ventricle and as
such you're going to go ahead and get depolarization of the ventricular
myocardium early before it occurs through the history Kinji system and
we'll show you what that looks like on the EKG and that'll make sense now
because there is depolarization of the ventricular myocardium you may see a
slightly longer QRS complex so basically if you were to look at this this is the
kind of situation that you're going to see you're going to see a normal P wave
but normally what you would see is you would see a normal q r s and then a T
wave right but in this situation you're going to see a little bit more than that
because again here's this accessory pathway that's coming over and so you're
going to start to see depolarization early and so this curving up is known as
a delta wave and that is pretty characteristic of WPW so if you see a
delta wave think about WPW also notice that the PR interval here to here is
going to appear to be smaller because of this Delta wave so let's take a look at
some real examples of what this looks like on an EKG so this is a patient with
WPW you can see right away that you've got this Delta wave here it's pretty
much all over the place you can see this Delta wave of course going in the
opposite direction because we're talking about AVR here you can see a delta wave
here you can see a delta wave and again we're talking about that pre excitation
of the ventricle so Delta waves in front of all of these QRS complexes here's a
nice Delta wave as well Delta wave as well okay so
these are all delta waves consistent with WPW okay and as we mentioned this
is a congenital problem and people can present with this at all ages as
children as adults they usually have you know symptoms of cardiomyopathy
shortness of breath things of that nature
there are three areas where you can run into problems with ventricular
tachycardia the first one as we were talking about is that this bundle of
Kent which is an accessory pathway can have rapid conduction in an antegrade
fashion so you can imagine that if somebody went into atrial flutter for
instance or they went into atrial fibrillation that all of those atrial
contractions will be transmitted perfectly through the bundle of Kent and
right on down into the myocardium and that would be a one-to-one conduction so
you know that atrial flutter waves for instance are sawtooth and they are going
to be going at about 300 beats per minute and so you can imagine a
ventricular rate of 300 beats per minute is going to lead to basically
ventricular fibrillation and that could be a fatal arrhythmia and so number one
the first problem that you can run into here is basically anterior grade
conduction because there is no no refractory period it just keeps
conducting it's like a wire basically that's short-circuiting it the second
possibility is that some of these bundles of Kent's believe it or not will
actually have an automatic foe site in it just like a pacemaker and it may
decide to go off and send a signal down and to the ventricle and that could
cause tachycardia yeah there's another way an accessory pathway can cause
problems sometimes these pathways can conduct exclusively in the retrograde
direction in other words not from the atria to the ventricles but from the
ventricle to the atria this is called a concealed accessory pathway because you
don't see the typical WPW pattern of a delta-wave and a short PR now can these
cause problems absolutely for example you could have a final atrial node
depolarization causing contraction going to the AV node going down the hiss
Purkinje system and then all the way to the end and then it signals the bundle
of Kent and transmits the signal back up and you have a reentrant
tachycardia and that would be a problem in that situation it would be narrow
complex but it'd be re-entrant and it would be going through the AV node so
back and forth back and forth I think probably one of the more testable
questions that you would see on a test regarding this is regarding specifically
atrial fibrillation so what happens if somebody has WPW and they go into afib
well you know that there's gonna be multiple contractions going on up here
greater than 3 400 500 beats per minute and it may be very very rapid so the
thing is is that these are going to be transmitted down into the AV node which
is right here but also through the bundle of Kent into the ventricle what
we don't want to do and this is really important what we don't want to do is we
don't want to block the AV node if there's a atrial fibrillation with
wide-complex because if it's a wide complex than we
know it's going through the accessory pathway and it's pre exciting down here
if it's a narrow complex completely narrow then we have no problem giving AV
nodal blockers because we know that it's going through the AV node but if we have
atrial fibrillation with WPW and there's kind of a widened QRS meaning it's using
the accessory pathway then if we use a beta blocker or if we use specifically a
calcium channel blocker it's gonna block only this AV node and it's gonna have no
effect on this accessory pathway and in that situation this could turn into
ventricular fibrillation and death so I think they want you to know that on
tests they want to make sure that you understand that so remember this WPW
with atrial fibrillation you really want to get them out of atrial fibrillation
as quickly as possible so if the patient is unstable you need to go to DC
cardioversion basically shock okay synchronized cardioversion okay now if
they are stable then don't use the non dihydropyridine calcium channel blocker
like verapamil and diltiazem and things like that that's just gonna make the
heart rate go faster and they may actually go into tricular fibrillation
what you ought to be using is if they're stable then you want to use medications
like procainamide or amiodarone
so that is the key now let's go back one more time and look at an EKG of WPW and
you can see again delta waves delta waves very short PR interval delta waves
well I hope this WPW video has been helpful to you if you want a
comprehensive EKG review however go to Meg cram comm where you'll see this
video with quiz questions and also a comprehensive review of EKG and if you
type in this coupon code you'll get a discount on the entire series I'll see
you go to make cram calm