Now, when you look at electrocardiograms and you interpret them, there's two things that go on.
The first thing is you get the gestalt.
That is the overall impression of the electrocardiogram.
Following that, you do a much more detailed analysis.
And I'm gonna go over that with you just in a moment.
So, 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's 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're better at pattern recognition than the computer with just makes measurements
and has a complex formula for reading the electrocardiogram
which is why the computers only write about 80% of the time and a human being needs to over read 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 the room,
if you'd go on to the Museum of modern Art in New York,
you would've said, "Oh, there's van Gogh's Starry Sky."
Why do you say that?
Because you've seen this painting so many times.
You know the style of van Gogh.
You recognize the pattern of van Gogh. Okay.
So here's a little quiz.
Who is this lady and who's the artist?
Of course you also recognize her because she's on poster.
She's on stamps. She's 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're going to recognize the pattern
but after that, you're gonna carefully reevaluate 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'll 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 increasing 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're 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's a nice P-wave in front of each QRS.
That the heartrate is normal and that the axis and the direction of the electrical impulses going in the heart is normal.
The QRS is normal. The T waves are normal.
So here's a normal electrocardiogram. How do you learn what a normal electrocardiogram is?
Well first of all, you 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 gonna 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 PQRST, PQRST.
In fact, there's no P waves.
And instead of the nice regular lub dub, lub dub, lub dub, you're hearing [abnormal heart sound].
You're 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 into the ventricle.
And the ventricle responds in a random fashion to all these beats --
electrical impulses that are arriving there.
This is a very common arrhythmia.
In the United States, about 10% of people of the age of 80 have these rhythm.
And there's a whole series of strategies for dealing with this.
And we'll talk a little bit about this when we get into therapy later.
So, remember the most important thing about the electrocardiogram is,
you wanna look at the gestalt.
You wanna 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 hundred percent of the time which is why a human being has to over read 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, in 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 over read on this.
The computer's often wrong in terms of recognizing rhythm analysis,
abnormalities in the rhythm of the heart.
The other thing that I think is important to say is that there's 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's 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's a joke I always tell the medical students about the man
who's on his way to a concert in New York at Carnegie Hall where all the best musicians in the world perform.
And he asked 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 was 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'd 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 disease.