00:01
Now let's look at a
Second Degree AV block.
00:04
Remember 1st-degree is
usually no big deal.
00:07
2nd-degree is getting
a little more intense
and 3rd-degree is the worst.
00:13
Now, do you remember how many types
of 2nd-degree AV block there are?
Good.
00:21
There's two.
00:22
And I love how easy
that is to remember.
00:24
I wish everything was but
let's enjoy it while we got it.
00:28
So 2nd-degree atrioventricular
blocks are occasional,
non-conducted P waves and
a prolonged RR interval.
00:39
Okay, that's really critical.
00:41
So underline that in your notes.
00:43
It's occasional, non-conducted P
waves with prolonged R to R intervals.
00:50
So we've got the two types Mobitz
type I which is also called Wenckebach
and Mobitz type ll.
00:58
2nd-degree AV block that means
occasional non-conducted P waves
with prolonged R to R intervals.
01:06
And you've got Mobitz type I which is also
known as Wenckebach and Mobitz type II.
01:12
So of course, we're going
to start with Mobitz type I,
one of the two types of 2nd-degree
atrioventricular blocks.
01:19
This one is known as Wenckebach.
01:22
Now, let me talk about
what's cool about this one,
I love it when you
find a strip with this,
because the PR interval gets
longer, longer, longer,
until you have a P
wave with no QRS.
01:34
So look at that strip.
01:35
If you pause the video
and you measured it,
the PR interval gets
longer, longer
and then you see a P wave right
where it's supposed to be.
01:44
But there's no QRS after it.
01:47
This is one of the important reasons
we ask you to always make sure,
are the P waves their
one to one for every QRS?
Do they all look the same?
This is so you don't miss a type
of block or other dysrhythmia.
01:59
So Wenckebach gets longer, longer,
longer until there's a P wave and no QRS.
02:06
So what's going on?
What's happening?
Well, in a Mobitz type I,
there's an intermittent conduction
block within the AV node.
02:16
And that's why you have a
failure to conduct the impulse
from the atria into
the ventricles.
02:23
Okay, so let's check that out.
02:25
You've got a PR interval, right?
So that means the impulse
is going through the atria,
it's making it to the
ventricle, that's the QRS,
then the second B,
you've got a PR interval, right?
We've got a P wave.
02:38
So it's going through the SA node, AV node,
it's making it through the ventricles.
02:43
Now we've got a P wave.
02:44
So it's moving
through the SA node,
oh, it didn't make it
through the ventricles.
02:49
So if you picture in your mind
what's going on in the heart,
see how it matches up with
what you see in the ECG.
02:58
So can you pause
the video and think,
why is there a P
wave without a QRS?
How would I explain that?
Okay, great.
03:09
Did you remember there's an
intermittent conduction block
within the AV node,
that's why it's an AV block,
that results in a failure
to conduct an impulse
from the atria to the ventricle.
03:22
So it just kind of
gets stopped there.
03:25
That's why you have a P wave, but no
QRS and Wenckebach or Mobitz type I.
03:31
So we usually don't
have to treat this,
we treat it depending on
the patient's condition.
03:37
If they're stable, they're able to
maintain a stable blood pressure,
they're not complaining
of any problems,
then it's usually considered
just a benign condition
that rarely causes
hemodynamic instability.
03:49
Asymptomatic patients,
we don't do anything with,
we leave them alone,
and we just keep an eye on it.
03:54
And check on that when
we see them for care.
03:57
So most people with Mobitz
type I or Wenckebach are fine.
04:02
It's benign, they're able to
have a stable blood pressure.
04:05
It's not a problem.
04:07
If they're symptomatic, then the next
step for treatment would be a pacemaker.
04:12
Now back to our chart.
04:14
So this is a great study
tool if you use it right.
04:18
Remember,
we're going to lay this out for you
as we continue through
this video series.
04:23
But the best thing you
can do for your study
is that you cover up these
boxes and use it as a way
to ask yourself and
then check the answer.
04:33
So you see we started
with 1st-degree,
we've already talked about that.
04:35
Remember,
it's technically not a block.
04:37
The only difference
between normal sinus rhythm
and a 1st-degree block
is the PR interval,
just a little bit
longer than normal.
04:46
So we don't usually
have to treat this.
04:48
Now 2nd-degree type I or
Wenckebach is also usually benign.
04:53
But the difference is we don't just
have a consistently long PR interval,
we have a PR interval that
progressively lengthens,
and then you have a
P wave and no QRS.
05:06
So usually this one
doesn't need treatment.
05:09
And if the patient
is symptomatic,
then we'll use a pacemaker to
treat the 2nd-degree Mobitz type I,
but that is not the norm.
05:18
Usually, the patient is stable,
and we don't have to
do anything with it.
05:23
Now let's go on to 2nd-degree
AV block Mobitz type II.
05:28
This is a little bit
different than the Wenckebach.
05:30
Now, look at the strip.
05:32
The P waves are at a constant
rate, you see that?
All the way across the strip,
we've got the P waves
just rocking along, right?
The PR interval.
05:44
Try and measure that right now.
05:46
Pause the video and
look at the PR interval.
05:50
Hey, that's different
than Mobitz type II,
because there's no prolongation of the PR
interval like we saw in Mobitz type II.
05:59
Now remember, a study strategy is
comparing similarities and differences.
06:03
So write in your notes,
what do you see right now that's a
similarity between type I and type II
and what do you see
that's different?
Now let's talk about the R to R intervals
as something we normally look at.
06:17
But look at this strip.
06:18
That looks a little
scary, doesn't it?
Yeah, as a student,
this would be really scary.
06:23
But know as a nurse,
we would be looking at the whole patient
and assessing them for their blood
pressure, how they're feeling,
we would make sure they
were hemodynamically stable.
06:34
So look at the R to R interval.
06:37
Now here we just have a couple, but if
you look at those, they're the same.
06:41
So the R to R interval is
stable before the dropped beats.
06:46
So it's the same before
the dropped beats,
but you just have to have a couple
hours together to actually measure that.
06:54
So the Mobitz type II can
sometimes happen secondary
to a disease involving
the His-Purkinje system.
07:01
Now there's a failure to conduct impulses
from the atria into the ventricles.
07:07
Ah, this is different, right?
1st-degree AV block, there's an
occasional or intermittent block.
07:15
But this one, there's a failure to conduct
it from the atria into the ventricles.
07:20
Now the block happens somewhere after
the AV node and within the bundle of His.
07:27
Let's go through
that one more time.
07:29
I know you will have this clear.
07:31
It's all about location,
location, location.
07:36
So there's something
going on usually secondary
to a disease or heart
disease in this patient
that would cause them
to have Mobitz type II.
07:47
We know that we have P waves,
but we don't have QRS complexes.
07:51
So we know that the impulse isn't making
it from the atria into the ventricle.
07:56
That's why we don't
have the QRS impulses.
08:00
But we also know
that the block occurs
after the AV node and within the bundle
of His or within the bundle branches.
08:09
So that's where Mobitz
type II happens.
08:12
And that's why you end up with
a strip that looks like P waves,
but not as many QRS complexes.
08:21
So do you wonder why there's
no change to the PR interval?
I bet you've already
got this answer.
08:28
Think about what the
PR interval represents.
08:32
Remember, the impulse
starts from the SA node,
then when it goes
to the ventricles,
the block hasn't happened yet.
08:42
That's why we have
a PR clear interval.
08:46
So the block happens
after the AV node.
08:50
So the His-Purkinje system like an
all or nothing conduction system.
08:54
So there's no changes
in the PR interval.
08:57
It's made it through the block
happens after the AV node.
09:02
So to clarify, in Mobitz type II,
there are no changes to the PR interval.
09:09
So no changes in the PR
interval in Mobitz type II,
are there changes in the PR
interval in Mobitz type I?
Yes. So that's one
of the differences.
09:22
Because in Mobitz type II,
there are no changes
in the PR interval
even after the
non-conducted P waves.
09:30
So that is a classic
difference between I and II
that you want to
help keep in mind.
09:36
But use our pictures.
09:38
Use the pictures to remember what's
being represented on the strip,
and these will be much
easier for you to master.
09:45
Now that you have the picture
in your mind that that impulse
is getting blocked
after the AV node.
09:52
What do you think could
possibly cause that?
Well type II blocks,
Mobitz type II blocks,
they kind of let us know there's
some type of structural damage
to the AV conduction system.
10:03
Now why this is more
serious than Mobitz type I
is that Mobitz type II often
deteriorate into complete heart block,
and that one is the
most serious of all.
10:16
So this is a big deal.
10:18
In 1st-degree AV blocks,
we usually don't treat it.
10:23
In 2nd-degree AV
blocks Mobitz type I,
we also usually don't
have to treat that.
10:29
If they are symptomatic,
we'll use a pacemaker.
10:32
In Mobitz type II, this patient is going
to require either a transvenous pacemaker
or a permanent pacemaker.
10:40
Now how do we pick?
Well, the transvenous pacemaker is
transvenous through the vein, right?
We just use that until the patient
can go for a permanent pacemaker.
10:51
But pacemaker is the
treatment of choice
for patients who are
symptomatic with Mobitz type I.
10:59
And for patients with Mobitz type
II because we know this rhythm
could deteriorate into
complete heart block.
11:07
So when this is recognized,
they definitely need a pacemaker.
11:12
So back to our chart,
you've got 1st-degree secondary type I,
2nd-degree type ll.
11:18
So I is not that big a deal.
11:21
II is usually benign,
but 2nd-degree type II,
we know because they
have an increased risk to
roll down into
3rd-degree heart block,
this one requires treatment.
11:35
Now when you compare
the PR intervals,
the 1st-degree is
greater than 20.
11:39
In 2nd-degree type I,
they get longer, longer, longer
until there's a P
wave and no QRS.
11:45
But in 2nd-degree type II,
that PR interval is constant,
except for the dropped QRS.
11:54
Now we don't really
need to treat I rarely.
11:58
II, we most often do
not have to treat it.
12:00
So 2nd-degree type I,
we don't have to treat.
12:04
But 2nd-degree type II will
receive an internal pacemaker.