00:01
Hi, welcome to our video
series on electrocardiograms.
00:05
In this particular part,
we're going to look at first, second and
third degree atrioventricular blocks.
00:12
Well, sometimes students think,
"Oh, this is so overwhelming."
But I promise you
it's really not.
00:20
Each one of these blocks
follows very specific rules.
00:24
So if you've hung with
us in our other videos
where we've gone
through the seven steps,
this will not be as difficult
as you may have heard
that other people think it is.
00:34
So let's start with
this first picture.
00:37
It's normal sinus rhythm.
00:40
Now we look at this
normal sinus rhythm
in every one of our
videos when we talk about
how to recognize
specific ECG rhythms.
00:48
But let's take a quick moment to some
key points that are going to matter
when we look at these blocks.
00:55
Well, you know that we have
a P wave for every QRS, right?
We're very thorough,
we always check that out.
01:01
If I plotted the distance from
P to P to P to P to P to P,
it's the same in
normal sinus rhythm.
01:08
If I measured the distance
between the R waves.
01:12
the very top of the peak of the
QRS, R to R to R to R to R,
it's also the same.
01:20
Those are hallmarks of
a normal sinus rhythm.
01:23
Once you have that
clear in mind,
the blocks make
a lot more sense.
01:28
So here's the seven steps
that I'm talking about,
that we've discussed
in each of our videos.
01:34
Now, if you need a little
more time with these,
just watch the
introductory videos
that we spend a lot of time
walking through each step.
01:43
So once again, let's recap.
01:45
Remember, the electrical impulse travels
from the atria to the ventricles,
and its trajectory is what gets
documented on the ECG strip.
01:54
Now at first,
the electrical impulse gets created
in the SA node or
the sinoatrial node,
then it starts traveling towards the
AV node or the atrioventricular node.
02:05
This causes contraction of the musculature
of the atria and formation of the P wave.
02:11
Now when the impulse
reaches the AV node,
it doesn't just pass through
it, it gets delayed.
02:17
This delay is documented in the
ECG strip as the PR segment.
02:22
So the PR segment corresponds to the
passage of the impulse through the AV node.
02:29
Next we have the QRS complex.
02:31
The QRS complex represents
ventricular contraction
which is caused by the
migration of the impulse
from the AV node to
the Purkinje fibers.
02:41
Moving on, we can see the T wave
which is caused by repolarization
or relaxation of the ventricles.
02:48
And as previously mentioned,
the interval between
ventricular depolarization
and repolarization gets
documented as the ST segment.
02:58
Finally, we have the U wave which
is believed to be the product of
delayed repolarization
of the Purkinje fibers.
03:04
But remember,
this wave may or may not be present
on an ECG strip that
you are interpreting.
03:13
So we've begun to talk about why
this ECG is normal sinus rhythm.
03:17
Let's see what you can recall.
03:19
P waves, one for every QRS.
03:22
The rhythm is regular.
03:24
Sometimes it can vary
during respirations.
03:26
But for the most part,
this will be very regular.
03:30
Now the P wave is positive
in lead I and lead II
and it's biphasic or a little
bumpy appearing in lead V1.
03:39
The rate ranges
between 60 and 100.
03:43
Now let's dig into the
atrioventricular blocks, right?
The AV blocks,
sometimes you'll see it written as AVB.
03:52
Okay, now we've got
a chart for you here.
03:55
And this is a great
way to orient yourself.
03:58
There are three
types of AV blocks.
04:01
They're not really cleverly
named as you'll notice.
04:05
They're 1st-degree,
2nd-degree and 3rd-degree.
04:10
Okay, so as we're
building our scaffolding,
we'll know we're talking
about atrioventricular blocks,
and that refers to the
atrioventricular node.
04:19
We have three types of blocks,
1st-degree, 2nd-degree and 3rd-degree.
04:26
And just so you keep in mind,
1st-degree is no big deal.
04:31
3rd-degree is the worst
one, okay?
That's the most
significant problems.
04:36
1st-degree, not a big deal if
they're not having symptoms.
04:40
3rd-degree, that's a big deal.
04:43
2nd-degree,
somewhere in the middle,
it depends on what else is
going on with your patients.
04:49
But since it's 2nd-degree,
it's easy for you to remember
there are two types of 2nd-degree.
04:57
Now there's a lot of
numbers going on here.
04:59
But 2nd-degree is
type I or type II.
05:03
They both used that funny
word before it Mobitz.
05:06
So 2nd-degree has two types
Mobitz type I and Mobitz type II.
05:13
Now let me ask you
a couple questions
to see if you can pause
and recall the information
about the types of AV blocks.
05:20
So look away from the screen and see
if you can answer these questions.
05:25
How many types of
AV blocks are there?
Right.
05:30
There's three.
05:32
What are the names of the 3
categories of atrioventricular blocks?
Good.
05:40
1st-degree,
2nd-degree, 3rd-degree.
05:43
Which is the most serious
category for AV blocks?
Cool.
05:49
3rd-degree.
05:50
Which category has
two types of blocks?
Right.
05:56
2nd-degree and they are Mobitz
type I and Mobitz type II.
06:01
So that exercise that you
and I just did together
is a great way for you to study.
06:06
Look away for your notes,
ask yourself some questions,
you're forcing your
brain to stop process
and recall and try and
retrieve information
so that you can make strong
connections in your neocortex.
06:19
So it'll be there when
you need it on a test
and when you're
caring for a patient.
06:25
So this strip is normal sinus
rhythm with 1st-degree AV block.
06:31
Remember that one is
not such a big deal,
your heart rates still going
to be between 60 and 100.
06:38
The rhythm is regular.
06:39
So so far, nothing different
than normal sinus rhythm,
because it is normal sinus rhythm,
it just has a little bit of a block.
06:49
Now the P wave may be buried,
might be a little difficult to find.
06:53
So just keep that in mind, that's why
your T wave might look a little different.
06:57
But the PR interval,
put a star by that.
07:00
That's the difference
between normal sinus rhythm
and normal sinus rhythm
with a 1st-degree AV block.
07:08
So this one is pretty
easy to recognize.
07:11
The PR interval is
greater than 20.
07:14
Okay, the QRS is still normal.
07:17
So the only thing that's different
from a normal sinus rhythm strip
to a normal sinus rhythm
strip with 1st-degree AV block
is the PR interval is
longer than normal.
07:30
Because remember, the PR represents
the passage of that impulse
through the AV node.
07:35
When the PR is greater than 20,
this tells us that
there's a delay
outside of what normally happens
in the conduction system.
07:44
Now something important
to keep in mind
is that the stimulus always
reaches the ventricles.
07:50
So technically,
it's not a block.
07:53
So for 1st-degree AV block
treatment isn't usually required.
07:57
The patient's healthcare
team will monitor the patient
and look at the cardiac
rhythm over time
to see if it worsens or
further issues develop.
08:06
So remember, the only difference
between normal sinus rhythm
and normal sinus rhythm with a
1st-degree AV block is which measurement?
Right.
08:16
The PR interval will
be greater than 0.20.
08:20
So we've got a
chart for you here.
08:22
Let's go over that again.
08:23
If it is a 1st-degree block,
it's technically not a true block
but we still use that verbage.
08:29
The only thing different is
the PR interval is longer
and it usually does
not require treatment.
08:36
They'll just keep a regular
checkup on the patient
to make sure things are still
staying at a first degree AV block.