Stress Tests – Invasive and Non-invasive Tests (Diagnostics)

by Joseph Alpert, MD

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    00:00 tests, such as the imaging tests with stress, either exercise stress or a drug stress.

    00:00 There are some general rules that should be followed whenever one is thinking about ordering a test. For example, don’t order a test that makes no difference. You want to order a test that’s going to affect what you are going to tell the patient and, of course eventually, what therapy you are going to recommend or further testing.

    00:22 If you already know the answer, don’t order the test because every test has a small chance of complication and you want to know, if the complication occur, that you really wanted to order the test. Know that some tests give less information than others. The exercise test with the electrocardiogram alone does not give us much information as the exercise test or the drug stress test when you are also using imaging. For example, nuclear imaging or echo imaging. And finally, it’s important to integrate the test with whatever information you already have about the patient.

    01:03 So, remember from our first part, last time, I talked about how important it was to understand the history. If you already have a strong suspicion that the patient has coronary artery disease, that is atherosclerotic coronary disease, then your test is going to confirm that. If you are doing it because you really don’t think the patient has this disease and that the chest symptom the patient’s reporting is really related to something entirely different, for example arthritis, you may not even want to do the test because you already have the answer. So, you have to integrate your desire for the test with your clinical suspicions obtained from the history and the physical examination.

    01:45 Now, the EKG stress test is the simplest, the cheapest and the most easily done of all the tests. The only imaging is with the electrocardiogram. And there are specific changes in the electrocardiogram which suggest that there is ischemia present. It’s the least accurate of the tests, but it’s the simplest and the cheapest and so, often, it’s the first test that we do.

    02:10 So, when we are doing the EKG exercise test, it’s either done on a bicycle or a treadmill.

    02:18 We record the electrocardiogram continuously. And then we decide, based upon the response of the electrocardiogram, whether there was a suggestion of ischemia or not.

    02:32 And here, we see just a little cartoon of somebody walking on the treadmill. They will be all hooked up to the electrocardiogram and we will be looking for the stress-test response. Here is two examples of EKG tracings. One is at baseline at the top and the one at the bottom is at peak exercise. You will notice that there is a decrease, a drop, in the ST-segment, that is the area of the EKG immediately after the big QRS. That is a so called ‘ischemic response’ and it suggests that there is part of the heart muscle that’s not getting enough blood flow. Remember the motor analogy? There is not enough gas getting into the motor and the motor is hurting, it’s not performing well and it shows you this ST-segment depression. This is a very typical example of a positive EKG exercise stress test. Now, of course, there are other tests that can be done with exercise or, sometimes with drugs to stress the heart to bring out ischemic heart disease. One of these is the echo. When the heart doesn’t get enough blood flow, of course we talked about this before, it doesn’t contract well.

    03:50 So, if you start off with a normal echo showing the heart functioning fine, the patient exercises and following exercise, there is an area of the wall that doesn’t move normally. That strongly suggests that there is lack of blood flow there and that the patient has atherosclerotic heart disease. So, this is an imaging test that goes with exercise that’s one step beyond the plain EKG test. We also record the ECG, by the way, during this so we have both the ECG information and the echo information.

    04:23 And here, we see the patient getting an echocardiogram. They may have just finished exercise, they quickly lie down and we record the echocardiogram with a very modern echo machine.

    04:36 Now, we don’t do this with stress, but occasionally, we want to get a more elaborate picture of the heart than we can get by putting the jelly and the probe on the chest wall. We want to get closer to the heart. It turns out we have a little echo on the end of a catheter that can be threaded down the throat behind the heart in the esophagus. So, you can see that the probe is right next to the heart and we get exquisitely detailed images here. This is not so much a stress test, but it’s more a very detailed anatomical test.

    05:09 I will just show you some examples. Here is an echo in a patient with a large dilated, poorly contracting heart that was done transthoracically. And, of course, these are movies, so the heart’s moving, you can actually see the motion of the heart and the motion of the valves. During this time, there are parts of this test where we can see whether the valves are leaking or whether they are stuck and so forth. Here you can see the contrast between the image you get with a transthoracic, that is when you put the probe right on the chest with some jelly as opposed to putting the probe down the esophagus with a tube. You can see, on the left, the transthoracic image of the aortic valve and on the right, you can see the transesophageal image - much more detail, much clearer look at the aortic valve.

    06:02 This is particularly useful if we think there’s an infection on one of the heart valves. You get a much better picture of the heart valve when you use the transesophageal echo.

    06:12 And we can even, in these days, we can do three-dimensional echocardiography. And I am going to show you an example of that in a moment.

    06:22 By the way, here is a transesophageal echo that shows a small blood clot in the heart.

    06:27 And this patient would need to be on blood thinners - anticoagulants, to prevent that little blood clot from breaking off and going to the brain and causing a stroke.

    06:37 As promised, here is a three-dimensional colorized - this is not the natural color. The computer enters the color to show contrast of depth and so forth. This is a three-dimensional echocardiogram of the aortic valve. And you can see that it’s quite detailed. We really… It’s a really excellent picture. Now, going back to the stress test, we can

    About the Lecture

    The lecture Stress Tests – Invasive and Non-invasive Tests (Diagnostics) by Joseph Alpert, MD is from the course Introduction to the Cardiac System.

    Author of lecture Stress Tests – Invasive and Non-invasive Tests (Diagnostics)

     Joseph Alpert, MD

    Joseph Alpert, MD

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