muscle for the next heartbeat.
Now, when you look at electrocardiograms and
you interpret them, there is two things that
go on. The first thing, is that you get the Gestalt -
that is the overall impression of the electrocardiogram.
Following that, you do a much more detailed
analysis and I’m going to go over that with
you just in a moment. So, why… why are human
beings so good at this idea of the Gestalt?
The reason is, we are excellent at pattern
recognition. This probably goes way back in
our evolutionary history when we were on the
African Veldt and you wanted to be able to
figure out patterns out there that told you,
“Hey, there is an animal I might be able
to eat or there is an animal that might be
able to eat me.” You needed to recognize
these patterns at a far distance so you could
make movements to escape, if it were an animal
that you thought that was actually threatening
to eat you. So, in natural selection, the
Darwinian Natural Selection, we have developed
a brain which is wonderful for pattern recognition.
The truth is, we are better at pattern recognition
than the computer which just makes measurements
and has a complex formula for reading the
electrocardiogram, which is why the computer's
only right about 80% of the time and a
human being needs to overread the cardiogram.
Let me give you an example. Look at that painting.
If… of course, you see who did it by the
information that’s there on the side, but
if you had seen this painting across a room,
if you had gone to the museum of modern art in
New York, you would have said, “Oh, there
is Van Gogh's Starry Sky.” Why do you say
that? Because you have seen this painting
so many times, you know the style of Van Gogh,
you recognize the pattern of Van Gogh. Okay.
So, here is a little quiz. Who is this lady
and who is the artist? Of course, you will
also recognize her because she is on posters,
she is on stamps, she is on toys. This
is of course, the Mona Lisa by Leonardo da
Vinci. Again, you recognize the pattern immediately.
That’s because the human brain is so wonderful
at picking up patterns. So, that’s something
that happens with reading the electrocardiogram.
You are going to recognize the pattern, but
after that, you are going to carefully re-evaluate
the electrocardiogram by looking at each specific
part. The P waves, the PR interval, the QRS,
the width of the QRS, the QT interval, each
of these will be examined. You will be looking
at the direction that the electrical activity is
taking through the heart, the size of the
various components, the P waves, the QRS and
the T and so forth. All of these carry information
about not only the cardiovascular system,
but also underlying electrolyte situations.
For example, marked increase in potassium
in the blood will cause changes in the electrocardiogram
and so forth. So, again, first the Gestalt,
then a very careful detailed analysis of each
part of the cardiogram and then you arrive
at a diagnosis. It goes without saying that
the more you know about the patient, the more
you are going to be able to pull out of the electrocardiogram.
So, let’s look at a couple of real life
electrocardiograms. This one is normal. You
can see, or at least I can see that there is
a nice P wave in front of each QRS, that the
heart rate is normal and that the… the axis,
in other words, the direction that the electrical
impulse is going in the heart is normal, the
QRS is normal, the T waves are normal. So,
here is a normal electrocardiogram. How do
you learn what a normal electrocardiogram
is? Well, first of all, we have a number of
rules and second, practice, practice, practice.
Reading electrocardiograms is like playing
soccer or playing tennis or playing a musical
instrument, it’s a question of practice.
There are going to be variations in normal.
You have to recognize those variations in
normal and distinguish them from abnormal.
Here we see, a very abnormal electrocardiogram.
You can see on the leads on the left hand
side that there is elevation in the ST segment.
This is a patient with an acute inferior wall
myocardial infarction, this is a patient,
I think everybody now knows, we want to take
quickly to the catheterization laboratory
and open up their coronary artery to stop
the damage that’s going on in the heart
muscle. Here we see an example of an abnormality
in rhythm. I think it’s obvious to you,
it’s not the nice, regular P-QRS-T, P-QRS-
T. In fact, there is no P waves. And instead
of the nice regular “lub dub, lub dub, lub
dub”, you are hearing “lub-dub, lub dubdub,
dulub dub, lubdub, dub dub lub, lub duhduhduh,
dubub-dubub”. You are seeing a completely
irregular heart rhythm and actually, quite
fast. This is atrial fibrillation in which
the normal atrial progression has been lost.
There’s… the atria is just fibrillating,
firing a whole bunch of beats down to the
ventricle and the ventricle responds in a…
in a random fashion to all these beats, electrical
impulses that are arriving there. This is
a very common arrhythmia. In United States,
about 10% of people of the age of 80 have
this rhythm and there is a whole series of
strategies for dealing with this and we will
talk a little bit about this when we get into
So, remember, the most important thing about
the electrocardiogram is you want to look
at the Gestalt, you want to interpret all
of the various subtle findings by looking
at each one individually. You want to remember
what the patient was complaining of and try
and integrate all that information with the
electrocardiogram and this will bring you
eventually to a diagnosis. Again, the computer
is right about 80% of the time, but not a
100% of the time, which is why a human being
has to overread the computer. So Gestalt,
meticulous calculation and examination of
the ECG, remembering it in context with what
you heard from the patient already. In conclusion,
then, reading an electrocardiogram takes a
lot of practice and a lot of time. You look
for the overall Gestalt of the cardiogram,
just like looking at the Leonardo da Vinci
painting. You then do a meticulous analysis
of the rate and the axis - that is the electrical
direction, you look for abnormalities in the
P wave and the QRS and the T and you put that
all together with your knowledge of the patient.
Remembering that the computer is only about
80% accurate, that there has to be a human
overread on this. The computer is often wrong
in terms of recognizing rhythm analysis, abnormalities
in… in the rhythm of the heart.
The other thing that I think it's important
to say, is that there is prognostic information
in the ECG. Often you can tell if a lot of
the heart muscle has been damaged or the heart
muscle is intact and healthy or there is too
much heart muscle, a lot of this tells you
something about how the patient’s going
to do down the road, particularly when you
put it together with your clinical information.
And remember with respect to the electrocardiogram,
practice, practice, practice will enable you
to read electrocardiograms effectively. There
is a joke I always tell the medical students
about the man who is on his way to a concert
in New York at Carnegie Hall where all the
best musicians in the world perform, and he
asks a native New Yorker on the street, “Can
you tell me how to get to Carnegie Hall?”
And the person answers to him, “Yes, practice,
practice, practice”. Of course, the person
he asked has misinterpreted, not knowing that
what he wants to know is - how do I walk to Carnegie
Hall, but rather how do I get to Carnegie
Hall to perform. The answer is the same with
almost any skill that you work on, you need
to practice, practice, practice, whether it
be electrocardiography, music or sports.
Thank you very much for being with us for
this third lecture on the Diagnosis of Heart
Disease. The fourth lecture will continue
this pattern as we talk about a variety of
tests that we use for further exactly diagnosing
what is wrong with the patient with heart