Hi, welcome to our series
on the electrocardiogram.
On this portion we're going to talk
about Wolff-Parkinson-White syndrome.
Now we always start
with a normal sinus rhythm.
So see if you can pause and
recall as to why this particular rhythm
we consider to be normal sinus rhythm.
Alright, no matter what
you got there remember,
stopping and trying to recall
information from your own brain
is the most effective study strategy.
Now let's quickly recap
what an ECG strip looks like
when a heart is beating
in a normal sinus rhythm.
There's a P wave with a normal shape
and duration preceding every QRS complex.
The rhythm is regular, but remember
that it can vary slightly during respirations.
Also, the rate is within the normal range,
which is between 60 and 100 beats a minute.
And lastly, these P waves are
positive in leads I, II, and biphasic
mean they have kind of like a
little notch in them, in lead V1.
With these basic characteristics, you know that
this is a healthy heart in a normal sinus rhythm.
You're really getting good at this.
Now in with all of our practicing,
when a patient comes in with this ECG,
you already know that this
isn't a normal sinus rhythm.
This patient has
Let's take another look at our
beating heart here and do a brief recap
on the waves and intervals of an ECG strip.
Remember, the electrical impulse
travels from the atria to the ventricles
and its pathway an influence on the heart
muscle is what's reflected on the ECG strip.
Now the impulse originates
in the sinus or the sinoatrial
or here's a third name, the SA
node, they all mean the same.
It travels from the SA node
through the left and right atria,
causing their contraction which is
reflected in the ECG as the P wave.
The impulse then heads through to the
AV node, but it doesn't just pass through,
it gets delayed or slowed down.
This delay is documented in
the ECG strip as the PR segment.
Next, we have the QRS complex,
which represents ventricular contraction.
This contraction is caused by
the impulse entering the ventricles
and dispersing through the Purkinje fibers.
The next wave is the T wave,
which is caused by the repolarization
or relaxation of the ventricles.
This period of time or interval between
ventricular depolarization and repolarization
is represented as the ST segment in an ECG.
Finally, we have the U wave, which actually
may or may not be present on the ECG strip.
Although we don't exactly know what
causes it, it's believed to be the result
of a delayed repolarization
of the Purkinje fibers.
Well, WPW is a congenital condition in
which the impulse originates in the SA node,
or somewhere else inside the atria,
but it doesn't pass through the AV node.
So if it doesn't pass through the AV
node to get to the ventricles instead,
it travels down an abnormal
accessory conduction pathway
that bypasses the AV node.
This accessory pathway is
called the bundle of Kent.
In Wolff-Parkinson-White or WP W, the
ventricles are depolarized faster than usual.
So because the normal delay that
happens in the AV node doesn't take place,
This is called the
preexcitation syndrome or PES.
So this is a heart condition in which part of
the cardiac ventricles are activated too early.
See, without the AV node delay, the
period of time between the atrial depolarization
and ventricular depolarization shortens
meaning the PR interval shortens.
Again this is how the impulse should travel.
And here it is how it travels in a heart with
Let's talk about the symptoms of WPW.
Symptoms most often appear
between the ages of 11 and 50.
However, it is one of the most common
causes of a fast heart rate in infants and children.
Now caution you, you know
that infants and pediatric patients
have faster heart rate patients than adults.
But we're talking about fast
heart rates that are problematic.
So WPW is one of the most common causes of
fast heart rate problems in our pediatric population.
Now how it will feel when
that heart is going too fast?
It will feel like they have this rapid pounding
They're going to feel dizzy, because
they're not being perfused very well,
and they're going to feel light headed.
Anytime you're looking at a list
of symptoms, ask yourself why.
So why would the patient say they feel
like they have a rapid pounding heartbeat?
Well, that one's easy, because they
have a rapid pounding heartbeat, right?
It's going through that accessory pathway.
It's going faster than normal.
And that is why it feels like that to them.
Do you remember what we talked about
why they would feel dizzy and lightheaded?
Good, I hope you said, Well, they're
not perfusing their brain very well,
because that rapid heartbeat doesn't
pump as efficiently as normal sinus rhythm.
So the more you can picture
what that looks like, into your mind,
what it would feel like as a patient,
you're going to ask better H and P questions,
better assessment questions, and
you're really going to be able to recognize
the signs and symptoms when you
see a patient who's struggling with WPW.
So let's start looking at
the ECG criteria for WPW.
Now it's all about the delta wave.
Now look, we did the P the Q,
the R, the S, the T, the V, the U.
what's a delta wave?
Well, a big hint is if you look at the
changes, the difference in the QRS complex
you see in this strip, in what
you saw in normal sinus rhythm.
Well, if you start moving
through those seven steps,
what do you identify is different?
Well, hopefully you picked up the presence of
the PR interval is much shorter than normal, right?
It's pretty close, right up to what we see is
the QRS, but that QRS looks kind of weird.
Look, it's it's wider than normal, and it's
actually wider than the normal range of 0.12.
Now they call this kind of a
slurred onset of the QRS waveform.
That's actually the delta wave.
So instead of looking like a typical QRS where
we have Q, straight up R, straight back down S.
This one has a kind of a slurred onset.
It looks like a lazier curve moving up there.
In that part of the waveform,
that's the delta wave.
Now you'll always see it
in the early part of the QRS.
So that is something to look for in WPW.
Two things: short PR and that slurred
start up to the QRS, and that's the delta wave.
Okay, now we've brought this in the black
line is if this was just a normal sinus rhythm beat.
That's why we have a normal PR interval, we've
got QRS, the T wave that all looks normal.
But why I wanted to show you this is I wanted
them to draw in in a green line and shaded area,
that's the area that's
different in a delta wave.
So if I'm looking at a normal sinus rhythm, I
would see that black line that's how it would look.
But a delta wave, the part of the QRS
complex that changes will be shaded in green