Rules for Ordering Tests – Invasive and Non-invasive Tests (Diagnostics)

by Joseph Alpert, MD

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    00:00 things that the chest X-ray can help us with. I am now going to ask you some questions that relate to which diagnostic test to use and under which conditions. And I hope that you won’t immediately jump to the answer, but that you will think about your answer and then see what my answer is. So, here is the first question. This is a patient who is 90 years old, who comes to the hospital complaining of some chest discomfort and has a slightly abnormal electrocardiogram. This patient lives in a nursing home and has severe dementia, in other words - doesn’t know family, doesn’t answer questions, doesn’t know where they are. Would it be appropriate to take this patient to the catheterization laboratory? Well, this is in part an ethical question, which the family and the patient have to discuss. But in general, I think we probably would not take this patient to the catheterization laboratory because it’s very unlikely we are going to make any improvement in this patient’s quality of life. They are already severely injured in terms of their severe advanced dementia. It’s unlikely we would make any benefit for this patient by doing a heart catheterization. Here’s the answer to this one that I just said. It’s unlikely we would improve this patient by doing a heart catheterization.

    01:19 Now, in this next slide, the question occurs - should we do two tests that give us the same information? And the answer is obviously, no. We wouldn’t want to do that, so you wouldn’t need both a CT angiogram, for example, and a cardiac catheterization. They would give us the same answer. If we did a CT angiogram and the images weren’t good and we weren’t sure, of course, we might go on to an angiogram. But, in most cases, you will just do one test that gives you the answer. You don’t need to do two tests.

    01:54 Another example would be a patient who had a completely negative stress test. Would you rush off and do a cardiac catheterization? Unlikely. Occasionally, you might if there were some question in the stress test as to how accurate it were... the images were. But in general, you won’t do another stress test or another catheterization test in a patient where you are pretty sure already that this is not ischemic heart disease.

    02:22 And again, before ordering any test, review in your mind the patient’s clinical information and exactly why you are doing the test. Do we really need this test? Is this going to give us an answer that’s going to change our approach to the patient, particularly with therapy? If it’s not going to change anything, don’t order the test. You are wasting money and you are putting the patient albeit at a very small risk of some complication.

    02:51 Again, remember that when the patient has already had a test that’s negative, you don’t need further testing. So, if you do an angiogram on a patient and the coronaries are normal, you don’t need a stress test to follow that because you already have your answer. One test has given you enough information that you don’t need further testing.

    03:12 Just to remind you, you should always think before ordering a test. This point I have made several times, but it’s absolutely important and it is frequently ignored. Are we really going to do something different based on the results of the test? In other words, don’t ask a question that makes no difference. You don’t need to order a test, if you already have the answer. If a patient has some chest discomfort and you do a nice stress nuclear test and it’s completely normal, you almost certainly don’t need to order a CT angio afterwards. You already have your answer. There is no ischemia in this heart. Even though the stress test is not perfect, it still strongly suggests that this patient does not have ischemic heart disease. And a CT angiogram would only give you the same result again. You would be doing two tests that would give you the same answer and not worth doing. Here’s an example of where a very simple test can give you a lot of information. You have a patient that has chest pain. We are concerned - does this patient have a STEMI or an ST-elevation myocardial infarction - a heart attack of significant size or do they have a non-ST-elevation myocardial infarction - a smaller infarct? Well, one of the tests that we can do, and we often do this in the Emergency Room, is we obtain a transthoracic echo. If the wall motion, that is the contraction of the heart is completely normal, it’s much, much less likely that this patient is having a heart attack. Certainly not an ST-elevation, substantial-sized heart attack and probably not even a small non-ST-elevation myocardial infarction, because almost always these are associated with decreased areas of wall motion - decreased contraction of the heart in certain regions. So, that’s very helpful. The patient comes in, has an electrocardiogram that’s somewhat confusing and this happens all the time. They have a story that’s somewhat confusing. You think, “Are they having a heart attack? Are they not?” The echo is a very helpful test. If it’s completely normal, the patient’s not having a heart attack. You can move on to consider other diagnostic categories.

    05:25 And here, we see just what I said to you. If the echo image is completely normal, it’s very unlikely that the patient has had an ST-elevation or a non-ST-elevation MI. Of course, if there are wall motion abnormalities, then we have to go further in exploring the possibility that the patient’s had a heart attack.

    05:46 This question asks - which is the best test for demonstrating ischemic heart disease? Well, of course, the absolutely best test is an invasive cardiac catheterization, but that carries some risks with it. Consequently, what is the best non-invasive test? The best non-invasive test is one that goes with imaging. It turns out that the echo stress test and the nuclear stress test are about equal in terms of their ability to define this disease.

    06:17 They are not 100% accurate, but they are in the neighborhood of 85-90%, which is pretty good when you combine that with your clinical impression. You can usually decide, “Yes, I think this patient is having problems from ischemic heart disease or not.” The MRI and the CT are a little less helpful because the CT might show you some atherosclerosis, but you don’t know if that’s causing the patient’s symptoms. You would like a stress test, you would like to bring out the symptoms, if you will. You would like to see the physiology, the abnormal physiology of lack of blood flow in the heart, either because of abnormal wall motion with the echo or because of abnormal blood flow distribution with the… with the myocardial perfusion imaging. And this slide just shows you what I just said that the imaging tests give you the most information, short of the invasive cardiac catheterization. And by the way, sometimes after the cardiac catheterization, we go on to do a stress test because we see some atherosclerosis in the coronaries, but we are not sure that that’s really causing a lack of blood flow. And so, sometimes we will do a stress test afterwards with an imaging study to see what’s the implication of some more moderate amounts of atherosclerosis. An important point to remember is the test you pick will also need to be integrated in your thinking about the patient. What were their symptoms, what’s their age and gender? It turns out that older people often can’t exercise enough to get a good increase in heart rate and blood pressure to really stress the heart, so you may order a drug test which can help show also abnormalities in blood flow in the heart. And so, again, there has to be some thought that goes into selecting which test you are going to do based upon the patient’s clinical presentation and also their age. Just another example, a patient with bad arthritis.

    08:16 You certainly shouldn’t send for an exercise test because they are not going to be able to walk sufficiently hard or bicycle sufficiently hard because of their arthritis.

    08:25 I mentioned before, the CT scan to look for calcium in the coronary arteries. This is a very good screening test. It turns out it’s a CT, or CAT scan that uses fairly low levels of radiation. So, the patient doesn’t get too much radiation. And what you do here is, if you see calcium, it means that the atherosclerotic process has begun in the coronary arteries.

    08:49 If you see a small amount of calcium, it means there’s probably not a lot. If you see a lot of calcium, it means that there’s probably significant atherosclerosis in the coronary arteries. But, it doesn’t tell you whether there’s obstruction in the coronaries because the atherosclerosis could be around the rim of the coronary artery, but the channel of the artery could still be wide open. So, we sometimes will combine a CT scan that shows a lot of calcium with some form of stress test or you might even, if you are very suspicious for coronary disease, go on to an invasive test. But, all this tells you is the burden of atherosclerosis. It doesn't tell you, is the atherosclerosis really interfering with blood flow in the coronary arteries. Now, sometimes we get a false positive test.

    09:37 What does that mean? That means the test says, “Oh! I think there might be ischemia in this heart.” But in fact, it turns out, it’s not true. There are a number of reasons for false positive tests. Particularly with the electrocardiographic exercise test, there can be about 10-15% false positives. The test has ST-segment depression, like I showed you, but in fact, when we do either an imaging test or a catheterization, the coronary arteries are normal. Sometimes it has to do with slight differences in metabolism of the blood vessels and the… and the myocardium. Sometimes it has to do with the inability of the blood vessels in the heart to dilate normally with exercise.

    10:17 But, it doesn’t mean that the patient is at high risk for a heart attack. So, sometimes we will see a false positive and we will have to follow that up with a more definitive test.

    10:29 So, an example of this is the 55-year-old woman who had a… some sort of chest pain syndrome, sort of atypical. You send her for an exercise test, it comes back positive.

    10:42 But subsequently, an imaging test of the blood flow on the heart shows that there is not ischemia, that this was a false positive test. Also, since a number of these tests give the same results, it’s important to know how well the test is done in your hospital. Let me give you an example. Some years ago, I was at the University of Massachusetts Medical Center. We did a drug test with imaging... with nuclear imaging using a drug called Persantine. And it showed distribution of blood flow in the heart when the radionuclide was given and the images were taken. Well, the person who invented this test and who described it in a very excellent article in the New England Journal was a fellow named Jeffrey Leppo. He was head of nuclear medicine at our place. We got more information when he read the test than if somebody in another hospital had read the test. So, we ordered a lot of these tests and then we would go down and talk to Jeffrey. He could squeeze more information out of the test than we could get from having somebody else look at it.

    11:47 Why? Because he knew the test better than almost anybody else in the whole world.

    11:51 So again, there’s going to be some reason to pick one test in your hospital versus another and it’s going to depend upon how expert the people are who are reading that test.

    12:02 So, in conclusion then, we have talked about a number of approaches to making cardiac diagnoses.

    12:10 Some of the tests are quite expensive and quite sophisticated. And others are much more basic and much less expensive. Which test you pick depends upon a whole variety of clinical factors - the age of the patient, the gender, their symptoms. You have to integrate all the clinical information to decide what’s the best test. And of course, you also have to know what’s the best test in your hospital. Remember, never order a test if you don’t care what the result is. Whether the test is positive or negative, you are going to do the same thing? Then certainly, don’t go ahead and order a test for which you have no need. Thank you for being with me today.

    About the Lecture

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

    Included Quiz Questions

    1. Coronary angiogram
    2. Chest x-ray
    3. Echocardiogram
    4. CT angiogram
    5. MRI
    1. An ECG, nuclear, or echo stress test
    2. Chest x-ray
    3. ECG
    4. Echocardiogram
    5. CT angiogram
    1. Electrocardiogram
    2. Chest xray
    3. Echocardiogram
    4. CT scan
    5. Magnetic resonance imaging

    Author of lecture Rules for Ordering Tests – Invasive and Non-invasive Tests (Diagnostics)

     Joseph Alpert, MD

    Joseph Alpert, MD

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