00:01
So let's start digging
into that ISO electric line.
00:04
So we're gonna ask you a question,
what exactly is
the ISO electric line?
Well, the answer is,
it's nothing.
00:15
The ISO electric line
is the flat line of the ECG strip,
where the electrical activity
is absent.
00:23
There's no or nothing
going on there,
there's no electrical activity.
00:29
So take a look at our strip.
00:31
We've outlined
the ISO electric line for you.
00:34
See it there?
Yeah, there's nothing
going on during that time.
00:40
Now, I know when you see P wave,
and then the sharp QRS.
00:44
Remember, the isoelectric line
is the average space
where nothing is going on.
00:49
You draw a line to connect
all those spots
where nothing is happening.
00:54
So between cardiac cycles,
the ECG recorder
returns to the ISO electric line.
01:00
So it goes to the P wave
isoelectric line,
QRS, then back
to the isoelectric line
before the T wave.
01:08
And then after the T wave,
back to the ISO electric line.
01:12
So between those cardiac cycles,
that's when the ECG recorder
or stylus returns to that line.
01:19
This is kind of our landmark.
This is where we measure everything.
01:24
The last piece I want you to know
about that isoelectric line,
or no electricity is going on,
is that a positive wave is the ones
that go above the isoelectric line.
01:35
We call that a positive deflection.
01:38
Now, negative waves
are below the line.
01:41
So take a minute,
circle or mark the waves,
you know as positive
by just putting a little plus sign
in your notes.
01:48
The ones that you see as negative
or a negative deflection,
mark those with a minus sign.
02:01
So on this one,
draw in the isoelectric line.
02:05
Follow it all the way through.
02:07
Does that make sense
that it would be placed there?
Well, right. It's the spot
that everything returns to,
and it means
there's no electrical activity.
02:16
But I want to talk about
three key points.
02:19
So we've laid
arrow one, two, and three there.
02:22
Let's look at the line this way.
02:25
Arrow one is the time before
the SA node sends the signal
through the left and right atriums.
02:33
Okay, so arrow one, that part of the
isoelectric line before the P wave
that represents the
time before the SA node
sends the signal through
the left and right atrium.
02:44
Now, between cardiac cycles,
it keeps returning
to that ISO electric line.
02:51
Second arrow.
This is the AV nodal delay,
which is the time between the atrium
and ventricle depolarizing.
02:59
This is what separates
the contraction of the atria
from the ventricles
to allow the ventricles to fill,
receive blood from the atrium.
03:08
Okay, that was a lot of words.
03:10
Let's pause and kind of
walk through this again.
03:13
We know the isoelectric line
is the flattest part, right?
That's where everything
returns back to.
03:20
Now, arrow two is telling us,
"Wow, it is made it
through the SA node.
03:25
Arrow two is the flat part
of the isoelectric line
that lets us know
it's the AV nodal delay.
03:34
Now, why do we need
an AV nodal delay?
Because we want the atrium
and the ventricles to work together.
03:41
So when the
atriums contract, right,
when they depolarize,
and they contract,
they squish blood
into the ventricle.
03:49
We don't want
the atrium and the ventricles
contracting at exactly
the same time.
03:55
That's just going to make chaos.
03:57
What we need is
atrium, small delay, ventricles.
04:02
Atrium, ventricles;
atrium, ventricles;
atrium, ventricles.
04:06
See what's happening here?
The atrium is being able to
increase the pressure, right?
So it contracts.
04:14
We need time for that blood
to make it
through the valve
into the ventricle
and for the ventricle to fill up
before it
contracts or depolarizes, and sends
blood on to the next destination.
04:28
So that little AV nodal delay
is really important
to an efficient heart.
04:34
So when you see that
right after the P wave
where we've marked it
with arrow two
that's exactly what's
going on in the heart.
04:43
Now, the third arrow.
This is the ST segment.
04:47
And you see those letters
there S and T.
04:50
This represents
the interval between
the ventricular depolarization
and repolarization.
04:56
So when the ventricle is depolarize,
and it contracts
then it repolarizes or relaxes.
05:04
And that's what you'll see
on an ECG
right there at arrow three.
05:08
Now, here's a note.
05:10
I want you to kind of
file away for later.
05:12
But if the ST segment is elevated,
now that means in comparison
to the isoelectric line.
05:19
If the ST segment is elevated,
or it's depressed,
compared to that isoelectric line,
this can let us know,
"Hey, something serious could be
going on with this patient's heart."
It might mean myocardial ischemia,
like chest pain,
where the tissue is still alive,
but it's really in trouble.
05:37
Or myocardial infarction,
which is dead tissue.
05:42
And remember,
dead tissue is stiff tissue,
and it's not able to
contract, and expand, or relax,
like we need it to
to be efficient.
05:52
So let's wrap up this part
of the video series.
05:56
Now, just as a gentle reminder,
each small box
is one millimeter on each side.
06:01
So, it's a one millimeter high,
one millimeter wide,
and that represents 0.04 seconds.
06:08
Each large box contains
five small boxes,
and represents 0.20 seconds.
06:14
Now, high amplitude and the QRS
may be seen in patients
with cardiac hypertrophy.
06:21
Low amplitude or voltage
may be seen in patients with
increased resistance
to current flow.
06:27
It could be obesity, COPD,
or pericardial effusion.
06:32
The isoelectric line
is the flatline of the ECG strip
where electrical activity is absent.
06:40
The ECG recorder
returns to the isoelectric line
between cardiac cycles
in the AV nodal delay
and after ventricular
depolarization.
06:51
By using the isoelectric line
as a landmark,
important ECG strip intervals
can be accurately measured
as one part of the process
to diagnose the health
of the patient's heart.
07:05
Thank you for watching
this part of our video series.