00:00
So now let´s get in to some of the pathologies.
00:03
You can see what a normal ECG wave looks like.
00:07
It has a normal P-wave, it has a normal QRS complex
it has a T-wave. These are all important electrical properties
of the heart. If someone has a disorder called atrial fibrillation
the top portion of the heart is the atrium.
00:27
And these two atrium will show up as the P-wave.
00:32
Therefore, if you have atrial fibrillation,
you should see abnormalities with the P wave
and you can see that.
00:40
Usually, what happens is
there's a lot of small jittery –
what looks like noise
in front of the QRS complex.
00:49
That is denoted as atrial fibrillation.
00:54
A first-degree AV block is
a block and where you have
a normal P wave,
but it takes too long to capture a QRS complex.
01:04
And how do you know it's too long?
It’s greater than 0.2 seconds.
01:09
That is a first-degree AV block.
01:12
A second-degree AV block is more serious than a first.
01:17
It means that there are certain times
when you have a P wave
and you don't capture a QRS complex.
01:25
Therefore, there is some
block in the AV system
that's preventing it from getting through.
01:32
A first-degree AV block
is just slowing down.
01:37
The second-degree AV block involves
some QRS complexes
that are not captured from that P wave.
01:46
The most serious is a third-degree AV block
and here you can see
a number of P waves with
no normal QRS complexes.
01:57
If there are QRS complexes that are generated,
they are generated ectopically
and therefore, have a wide QRS complex.
02:07
How do I know it's wide?
It’s greater than 0.1 seconds.
02:11
That’s where all those
intervals become important.
02:15
You have to be able to
identify what the interval is
and then know the normal numbers
that are associated with it.
02:25
PVCs can be seen quite often.
02:27
These can happen if you have,
again, a type III AV block,
but you can also get PVCs
to occur on a regular basis.
02:37
And here, you can see some PVCs
that are occurring in a sequence.
02:41
And if you have them occur fast,
that can be a ventricular tachycardia.
02:47
You notice that there is no isoelectric line.
02:50
You don't see any P waves.
02:52
All you have are these PVCs.
02:55
Even more serious than ventricular tachycardia
is ventricular fibrillation.
03:01
So, at least in ventricular tachycardia,
you are getting contractions of the ventricles
that was pushing out blood.
03:09
In ventricular fibrillation,
you have so many contractions happening,
it's not pushing out enough blood per beat.
03:18
And if you don't push out enough blood,
it doesn't circulate to the tissues.
03:22
And you end up having hypoxic tissues
and actually could die in this condition,
unless you got put on a defibrillator
and you received shocks,
and that is the best way to get out
a ventricular fibrillation.
03:40
There are number of other ways to look at the ECG.
03:43
And as you move through medicine,
you will just deepen your
understanding of what an ECG is.
03:49
I'll go through one other pathology with you
and this involves the
STEMI myocardial infarction,
which is a heart attack.
03:58
And I go through it just because it is
something that you all have heard about
are heart attacks
and be able to understand
or to recognize someone who had a
heart attack with an ECG is helpful.
04:11
So, you can notice the normal QRS complex
where you have a P wave,
a Q, R and S,
and then you have a T wave.
04:21
This can change
if you're exposed to severe ischemia
induced by lack of blood flow
to certain areas of the heart.
04:30
What happens in ischemia is
you have a decrease in membrane potential.
04:37
What do I mean by a
decrease in membrane potential?
It’s lower than normal.
04:42
So, if you have a lower-than-normal
membrane potential,
you start off on a lower level.
04:49
You have a normal P wave.
04:51
You might have a normal QRS complex.
04:54
But then you don't
return back to this low level,
which you had,
because of this ischemic event.
05:03
And so, you end up
being at a higher value for your ST segment.
05:08
And then you have a normal T wave.
05:10
This is called ST segment elevation.
05:15
And one of the key reasons why ST elevation happens
is because of a little bit of a trick on your eye,
which looks like the ST segment is elevated,
when actually it's the normal isoelectric line
that is before the P wave
or after the T wave,
which is suppressed, because of ischemia
and lack of oxygen to a certain portion of the heart.
05:42
And so, this is just a very
classic way to look at
or to find out
that someone has a heart attack
if they show up with an ST segment elevation.