Reading Ecgs – The Patient's History (Diagnostics)

by Joseph Alpert, MD

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    00:00 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.

    01:17 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.

    02:04 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.

    02:43 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.

    03:04 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.

    03:40 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.

    03:47 You have to recognize those variations in normal and distinguish them from abnormal.

    03:52 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.

    04:48 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 therapy later. 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.

    06:39 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 disease.

    About the Lecture

    The lecture Reading Ecgs – The Patient's History (Diagnostics) by Joseph Alpert, MD is from the course Introduction to the Cardiac System.

    Included Quiz Questions

    1. The first heart sound is caused by the closure of the mitral and tricuspid valves.
    2. The first heart sound is caused by the closure of the aortic and mitral valves.
    3. The second heart sound is caused by closure of the aortic and tricuspid valves.
    4. The second heart sound is caused by closure of the mitral and tricuspid valves.
    5. The first heart sound is caused by closure of the pulmonic valve.
    1. ST segment elevation
    2. PR interval prolongation
    3. QRS complex increased in size
    4. Absence of P waves
    5. Prolongation of QT interval
    1. Atrial flutter
    2. Acute inferior myocardial infarction
    3. Aortic dissection
    4. Acute anterior wall myocardial infarction
    1. Sum total of R wave
    2. Sum total of P wave
    3. Sum total of Q wave
    4. Sum total of QRS complex
    5. Sum total of T wave

    Author of lecture Reading Ecgs – The Patient's History (Diagnostics)

     Joseph Alpert, MD

    Joseph Alpert, MD

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