Now let's start with step four.
I want you to measure the QRS duration.
Now the QRS complex represents the
depolarization of the left and right ventricles.
Now it's made up of the Q wave,
the R wave and the S wave.
So see it, follow it with your finger.
You've got the isoelectric line
dips down, that's the Q wave,
then it shoots up to the top, that's the R wave,
and then back down again for the S wave,
and you see the isoelectric line again.
So the QRS for the left and right ventricles
is made up of the Q, R and S waves.
Now, ventricular depolarization is normally
what triggers the contraction of the ventricles
as we see that QRS happening on the ECG
strip, it's the contraction of the ventricles
that's actually happening in the heart.
Have you ever wondered why the QRS
is so much bigger than the P wave?
Well, I want to see if you can pause and recall
with what we've talked about each of these waves?
Why would the QRS be so much bigger?
Ready for the answer?
Well, ventricular depolarization involves a
greater muscle mass than that of the atria.
Remember that ventricle is responsible
for pushing blood into massive spaces,
that's why it is so much bigger and stronger.
The QRS is measured from the point where the
complex begins to move from the baseline,
and ends where the last wave of
the complex begins to level out,
or distinctly changes direction.
So take a look at the complex we have there.
Now we put two lines to give you an indication.
Look how that first line, you see, it's measured
where the complex begins to move from the baseline.
That's where you would start the measurement.
And then the second line we have in the spot
where you want to measure at the end of it.
That's where the last wave of
the complex begins to level out.
And we say level out meaning the isoelectric line.
Now, we can get into a lot of arguments
when we are interpreting strips.
So as long as you systematically and
consistently follow these guidelines,
you're going to have a much better
shot at getting something accurate
when you're doing your own ECG interpretation.
So you see where we start, you see where we end.
The space in between that represents time should
be the normal duration of the QRS complex.
So it should be from about .06
seconds to 0.12 seconds, okay?
So normal QRS is .06 to .12,
and that stands for seconds.
Or since you've already done the
math .12 would be 3 small boxes.
Now the QRS complex represents
depolarization of both ventricles,
but you only see one QRS, just
like you only see one P wave.
Even though both atria are
contracting, you see one P wave
because they're kind of
right on top of each other.
But when you talk about ventricles,
the left ventricle pushes blood out
all the way throughout the body, right?
So that left ventricle is
stronger than the right ventricle.
The left ventricle has a greater muscle mass.
It's because of its big job of shoving everything
out through the aorta to the rest of the body.
Now the deflection of the right ventricle is
often hidden by the larger left ventricle.
So one P wave, two atrium, one
QRS complex, two ventricles,
and likely what you're seeing is the left
ventricle, because it is much stronger
than the right ventricle.
Whoa, I thought we said we
weren't doing 12-leads here.
Well, we just put this in here
because I wanted you to take a look at
how QRS complexes can look in different leads.
Now, when we say different leads, you see where
we have these 12-leads placed on our patient.
Okay, each one of these little shots here I, right,
You've got the lead I, AvR, you see
the names of the different leads,
those are just referring to the direction
with which you're looking at the heart.
You'll notice that in certain leads,
the QRS is upright or positive,
and in other leads, it's negative.
Some of them it looks like wow,
the amplitude is really small.
That's all normal.
So essentially, we'll be talking most about lead
II, okay, so we'll be talking about lead II,
So find lead II and our group of 12
there, and you'll see that oh, okay,
that looks like we expect it to look.
You've got the P wave, you got the QRS and
you've got back to the isoelectric line.
That's how we're teaching you.
But know that there are 11 other leads
where things might look a little different
and still be normal.
Now there can be abnormalities in a QRS waveform.
A narrow QRS is normal as long as
you're within the normal parameters.
A wide QRS that's greater than .12 is abnormal.
See, a wide QRS means there's some trouble.
It could mean that the ventricles
aren't all contracting together.
And this might because you've got the
disruption of the electrical conductivity,
that is a bundle branch block.
Okay, so that means you've got things
moving through, but we've got a block
and so the electrical conductivity, it's
not able to move through as it would
in a normal heart.
So when you see a wide, kind of weird looking
QRS, it might be a bundle branch block.
We also see why QRS complexes when
the electrical inputs for the heart
originated in the ventricles
instead of the SA node.
Woah! We will show you some of those are
called premature ventricular contractions
is an example of a really weird looking QRS,
that the heartbeat originated in the ventricles
instead of the SA node.
So remember, SA node - top and
works down to the ventricles
but if we have something like a
premature ventricular contraction,
that's the ventricles way of saying,
'I'm going to do it my own way',
and the signal kind of goes backwards, so
that's why it looks so weird and bizarre.