Pulmonary Embolism: Diagnosis

by Carlo Raj, MD

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    00:01 Chest x-ray: nonspecific, okay.

    00:03 Now here, I wanna make sure that we're clear.

    00:06 This is a very important statement and if you're just memorizing this, you're gonna miss the question and we can't afford to do this right now.

    00:13 So what we can afford to do is make sure that we offer clarity.

    00:17 So what they PE? I want you to break off an emboli from the thrombus and move it up from the DVT, moving through the right side into the pulmonary artery.

    00:28 In your pulmonary capillary now.

    00:30 Okay. That is not my alveoli. Is the capillary - is that following to an alveoli? That makes no sense, right? So what am I getting at? If it's a PE, what kind of defect is it first and foremost? Is it a perfusion defect? Is it a ventilation defect or is it a diffusion defect? Good.

    00:52 It's a perfusion defect and Dr. Raj on this chest x-ray, why are you showing atelectasis? Good question. Because it can also occur.

    01:03 Okay? There's different phases of PE, pulmonary embolus and this, you wanna know clinically.

    01:09 If your patient has a perfusion defect, listen, per-fusion.

    01:14 That means that the blood supply through the alveoli has been cut off.

    01:18 Why? Because there's a fricking embolus there. Are we clear? That's no joke.

    01:24 So now, what about the alveoli? Is it filled with oxygen? That it is. So if this oxygen is filling up this alveoli, it can't participate in gas exchange.

    01:34 Why? There's no blood flow. Definition; pathologic dead space.

    01:40 Point number one, this is not what this bullet point is saying.

    01:44 At some point in time, is it possible that there's enough damage to the lung where therefore the alveoli will collapse? That it will. Then we have what? Atelectasis.

    01:55 Then what are you looking for in this patient? Oxygen has been given and guess what? You're not going to find improvement because the alveoli is dead. Scary.

    02:06 Okay. On chest x-ray.

    02:08 Atelectasis, I told you to be careful.

    02:10 Do not confuse this with interstitial lung disease. Is that clear? Atelectasis, hopefully that will give you a closer view of the chest x-ray and you can see collapse of the alveoli.

    02:21 Okay. Infrequently wedge shaped, so this will be pleural based, pulmonary infarct maybe then visible.

    02:28 And this would then appear as your red infarct and so therefore there might be a huge wedge by the periphery lateral aspect of the lung in which it then looks red.

    02:38 Well, oh - I'm sorry, this is chest x-ray, I thought it was find on gross examination.

    02:42 But then, at the wedge, is what you would find - chest x-ray would be very, very opaque, infrequently though, infrequently. Okay. EKG.

    02:51 What kind of things are you looking for PE? Nonspecific, but there is a specific - it's a cool little mnemonic have you that may then help you out with PE here and it's called S1-Q3-T3.

    03:04 Now what this is saying is - well, I'll show you this in the next upcoming slide where the Q3 and the T3 on your lead three.

    03:12 We're going to then take a look at the Q and the T and then the one refers to lead one, you'll see.

    03:18 This is all in EKG, that's the topic for this right now, EKG.

    03:21 So lead one and then on lead three, we'll take a look at the Q and T.

    03:26 We call this S1-Q3-T3, pretty cool I think.

    03:30 Then - well, this is what I told you right off the back.

    03:33 I asked you on basically the beginning of our PE lecture that you're breaking down your thrombin and you told me correctly that it's plasmin that's responsible for breaking it down. Good.

    03:44 Well, if you're breaking down your thrombin and your fibrin. Right? The fibrin is a strong - as long as your Factor 13, you have an insoluble clot and it's the plasmin that is then going to break down the fibrin.

    03:56 Welcome to D-Dimers. This is what you're gonna look for, right? Whenever your thrombi is breaking down and specifically if it's a more of your fibrin.

    04:05 When else would you find your D-Dimer? When you see the D, you're probably thinking about DIC.

    04:12 Are you breaking down tons of thrombi in DIC? Of course you are.

    04:17 Understand the concept of D-Dimer.

    04:19 Two major differentials though, I would say, it would be PE or DIC.

    04:24 Okay. Now on your EKG, this is S wave, S1.

    04:29 So what that means, it's not a heart sign.

    04:31 Lead one, the S wave is going to be abnormal here so that is going to be an issue.

    04:37 Next. In lead three, come down to lead three. And what is a Q wave normally? Okay, it's the first negative deflection, correct.

    04:47 But what if you find that negative deflection to be exaggerated? That's what you call a Q wave. Is that clear? So it's kind of a silly name, but I speak the language. And then you have T3.

    04:59 Once again in lead three, if you can, well here, I've blown it up. You see the T wave? It's going the wrong direction, it's inverted. You're clear? And that's what you're seeing here in the ECG.

    05:13 So for PE, be familiar with the clinical picture on EKG, known as S1-Q3-T3. Let's move on. Okay.

    05:25 Let's do arterial blood gas and we'll have hypoxemia even with rapid shallow breathing.

    05:30 Next. We're gonna have increased or widened A-aO2 gradient.

    05:35 Once again, if you're forgotten, as a general rule of thumb, the lung damage or any inter-pulmonary disease is going to cause a widening of the A-aO2 gradient.

    05:45 Let it be pneumonia, diffusion defect, perfusion defect, so forth, PE is both a perfusion defect.

    05:54 What if you had atelectasis? Ventilation defect. Are we clear? It's both - it could be both, it doesn't matter.

    06:02 Either case, you have a widening of the A-aO2 gradient.

    06:04 And you may just see a low pulse ox with exercise, so that's a little scary.

    06:09 Cuz the pulse ox here. Because the rapid shallow breathing might just show a little bit of lowering.

    06:14 But you have to have high suspicion about who your patient here is with the PE. Okay.

    06:20 Let's get into proper diagnosis and management.

    06:22 It is imperative that you know how to properly diagnose your patient PE.

    06:26 V/Q scan is the old first-line test. Keep that in mind though.

    06:31 Radionuclide scan that compares ventilation and the perfusion by the blood supply and that's something that you've discussed over and over and over again with the - in physiology.

    06:44 Make sure that you're completely familiar with V/Q. Do you remember the normal V/Q ratio? 0.8, okay. And so therefore, if it's less than 0.8, do you know what your breathing pattern is? You remember? Hypoventilation. If you're greater than 0.8, you're? Hyperventilating.

    07:01 And so those are things I'm just gonna point out here and in physio - you have to be.

    07:06 I mean that's one of the heavily tested - and really, every time you walk into a ward, guaranteed you're attending is gonna ask you something about V/Q.

    07:14 In a PE, there will be a V/Q mismatch where a segment is normally ventilated but not perfused due to vascular obstruction from the embolus and this is something that we talk about.

    07:24 So the segment normally ventilated. Right? So this would be the dead space.

    07:28 We're just going through the most classic picture of PE.

    07:32 So proper ventilation, but you do not have perfusion that's what that V/Q mismatch is - or the scan will then reveal that type of V/Q mismatch. Okay.

    07:43 The new first-line test is going to be spiral CT.

    07:47 So, could you get a question where it's asking about V/Q scan and spiral CT? Sure.

    07:52 That's how important things have now become in terms of management.

    07:56 Requires an IV contrast.

    07:58 Allows looking at lung to see if there is other pathology that explains the dyspnea and chest pain, so you kind of get a birds eye view literally of - well, is it the pure PE that's causing the dyspnea and such? And hence it becomes a very, very valuable tool; spiral CT scan.

    08:18 Now, angiography is the imaging test of choice.

    08:22 So imagine that now.

    08:23 It wouldn't be nice to have an image of the pulmonary vasculature angiography, correct? So CT, pulmonary angiography will be the imaging test of choice.

    08:37 In here, you would find once again, increased opacity, take a look at this.

    08:40 And on your, well, of your x-ray here.

    08:45 That area with increased opacity is going to be the area where you have a huge pseudo-embolus, our patient didn't make it.

    About the Lecture

    The lecture Pulmonary Embolism: Diagnosis by Carlo Raj, MD is from the course Disorders of the Pulmonary Circulation and the Respiratory Regulation.

    Included Quiz Questions

    1. S1Q3T3
    2. S3Q1T1
    3. Widened QRS
    4. New onset delta wave
    5. Polymorphic p waves
    1. V/Q ratio > 0.8
    2. V/Q ratio = 0.8
    3. V/Q ratio = 0.5
    4. V/Q ratio < 0.5
    5. V/Q ratio < 0.7
    1. CT pulmonary angiography allows for the identification of other lung pathologies.
    2. CT pulmonary angiography is more time-intensive
    3. Conventional catheter-based pulmonary angiography is less invasive.
    4. Conventional catheter-based pulmonary angiography is more cost-effective
    1. CT pulmonary angiography
    2. CXR
    3. V/Q Scan
    4. CT chest without contrast

    Author of lecture Pulmonary Embolism: Diagnosis

     Carlo Raj, MD

    Carlo Raj, MD

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