00:01
Okay.
00:02
Let's combine our augmented leads –
aVR, aVL, aVF –
with our standard limb leads,
1, 2, and 3.
00:11
So, now, we have six different
pictures of the heart
around one single plane.
00:18
So, this is along the frontal plane here.
00:22
And each of the arrow tips
represent where the positive pole is.
00:28
So, the negative pole is on the
opposite side of the arrow.
00:33
A depolarization traveling
towards a positive pole
is going to give you a positive deflection.
00:40
And again,
the maximal positive deflection will be
closest to that mean vector.
00:48
And then,
you need to look at
what is the wave perpendicular,
meaning that it would be a 90° angle
from the line that you drew
from that particular axis
that had the highest deflection point.
01:02
Okay, we’ll come back to this
and revisit it a couple of times,
but just have that in your mind
as we move forward.
01:11
One plane,
this plane right here;
six different views, you have them.
01:17
And we can all put them around one circle.
01:20
And algebraically, one circle is 360°.
01:24
So, we're going to give certain leads a degree.
01:30
And this is going to be a helpful way
for us to assess
if someone's heart is normal or not
based upon what degree their
mean electrical axis might be.
01:41
Okay.
01:42
We need to build on some of that process
and that is we need to talk about
what really is a mean electrical axis.
01:49
A mean electrical axis should be
somewhere in between about
negative 30 to 100.
01:56
That's the normal range for mean electrical axis.
02:00
Some people will say that
normal is in between 0 and 90,
and that's okay too.
02:06
I'm just giving you a little bit wider range.
02:08
Not everybody always agrees in medicine
what is normal and what's abnormal.
02:14
So, it's either 0 to 90
or negative 30 to 100.
02:18
Two good ways to think about it.
02:21
Your mean electrical axis should lie
somewhere in between that range.
02:29
Two pathologies will affect this.
02:32
If you have hypertrophy,
the mean electrical axis will
move towards a hypertrophy.
02:40
If you have a myocardial infarction –
that is a heart attack –
the mean electrical axis will move
away from the heart attack.
02:48
So, you move towards hypertrophy
or away from heart attack.
02:54
So, knowing that information,
let’s go calculate a couple.
03:01
So, let’s take this example here
and where we are looking first
for which particular wave
is the most biphasic.
03:10
What do we mean by biphasic?
Can't we just use simple words?
I know it's frustrating,
but let's work through it.
03:18
Biphasic means that your positive deflection
equals your negative deflection.
03:25
So, whichever electrode lead shows
an equal positive deflection
versus a negative deflection, okay?
So, it has to have a blip up and a blip down
and those two amplitudes
need to be very similar.
03:42
You're looking for that lead.
03:44
Then, you want to look for
the lead that’s 90° from it.
03:50
And you want to see
which one is 90° from it,
closest to 90° from it,
has a positive electrode deflection.
04:01
Okay.
04:01
Let's go through two examples.
04:03
Everybody needs examples.
04:05
When you first learn this, it’s very hard.
04:07
So, you just need an example.
04:08
You need to walk through a couple.
04:09
So, let’s take one.
04:12
If standard limb lead 1 is biphasic
and aVF is the most positive,
the mean electrical axis is 90.
04:23
So, if you traced this out,
you could see standard limb lead 1.
04:28
That’s that arrow that's going towards zero here,
right there.
04:33
That's going towards zero.
04:36
That would be your most biphasic.
04:41
aVF is located perpendicular
to standard limb lead one,
and that is a direct downward movement.
04:52
If that is a positive deflection,
that gives you your mean
electrical axis a positive 90.
05:00
If we take a second example,
let's say aVL,
so here we have aVL.
05:06
If that is the most biphasic,
you'd want to take what is 90° from that,
and so that would be
standard limb lead 2.
05:14
That’s standard limb lead 2,
therefore, you would have
the most positive deflection
that would give you
a mean electrical axis of 60.
05:26
Those two examples are
normal mean electrical axes.
05:30
Why?
Because mean electrical axes should be
somewhere between negative 30 and 100.
05:36
Both 90 and 60 fall within those means,
and therefore, that is a normal ECG.
05:44
Remember our two pathologies.
05:46
If you have hypertrophy,
it will cause a shift
towards the hypertrophy.
05:50
If you have an infarction,
it will shift it away from the infarction.