BackTable / VI / Podcast / Transcript #58

Podcast Transcript: Endovascular Treatment of Pulmonary Embolism

with Dr. Venkat Tummala and Dr. Thomas Tu

Interventional Cardiologist Thomas Tu, MD and Interventional Radiologist Venkat Tummala MD discuss their respective approach to the treatment of Pulmonary Embolism, including risk stratification, treatment options, and endovascular technique. You can read the full transcript below and listen to this episode here on BackTable.com.

(1) Indications for Endovascular Treatment of Pulmonary Embolism

(2) Endovascular Treatment Modalities for Pulmonary Embolism

(3) FlowTriever Pre-Procedural Evaluation

(4) FloTriever Thrombectomy Procedure

(5) Aspiration with the FlowTriever Device

(6) Dealing with Residual Clots

(7) Heparin Usage

(8) FlowTriever Technique

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[Dr. Michael Barraza]
Welcome to the BackTable Podcast, which is committed to all things IR and endovascular. This is Michael Barraza returning as your host. I'd like to thank our listeners for tuning in and encourage you to subscribe to the podcast on whatever platform you use to listen, or leave us a review on iTunes. We always appreciate your feedback.

Before we dive into our topic for discussion, I'd first like to thank today's sponsor, Inari Medical. Inari Medical's mission is to treat and transform the lives of patients suffering from venous diseases with purpose-built solutions for removing large blood clots from the venous anatomy without the need for thrombolytic drugs. The Inari FlowTriever is the first mechanical thrombectomy system indicated for the treatment of pulmonary embolism. Find out more information at Inarimedical.com.

Today, we're talking about endovascular treatment options for pulmonary embolism, or PE. Joining me today are Dr. Tom Tu, an interventional cardiologist, and Dr. Venkat Tummala, an interventional radiologist. Thank you both so much for doing this. How are you guys doing?

[Dr. Thomas Tu]
Great, thanks for having us, Michael.

[Dr. Venkat Tummala]
Thanks, Michael, doing great.

[Dr. Michael Barraza]
Before we start, I just thought maybe I'd have the two of you tell us where you are, what you're doing and then we'll go from there. Start with you, Tom.

[Dr. Thomas Tu]
Sure. I am an interventional cardiologist by training. I have been in practice in Louisville, Kentucky for over 16 years. I started treating pulmonary embolism with a lot of interest and regularity about five years ago and because of my work with the initial product of Inari Medical, I've actually taken a full-time job as chief medical office of Inari Medical at this time.

[Dr. Michael Barraza]
Right on. Yeah, actually I heard from somebody recently who heard you speak and he shared an interesting story about how you started doing this in your first case. Would you mind sharing that?

[Dr. Thomas Tu]
Sure. Education of cardiologists in the field of venous thromboembolism was quite lacking in my medical training. All I knew from medical school and residency was pulmonary embolism was bad and that you treat it with anticoagulation and you hope for the best. And as a practicing cardiologist, I was asked to treat a patient with pulmonary embolism who had failed systemic thrombolysis. This was about two years into my practice and the chief of the intensive care unit asked me to help this 30-year-old health care worker who was dying of a massive PE due to a ruptured appendicitis. And they had given systemic thrombolytics. The patient did not re-perfuse, they were hypoxic and in shock and really I had to make things up as I went along. I ended up doing things like a thrombectomy with AngioJet, which we had at that time, swirling pigtail catheters in the pulmonary arteries and surprisingly, this patient survived and that really inspired me to do better for our patients with this disease state.

[Dr. Michael Barraza]
Now, Venkat. I also would like you to tell us where you are and what you're doing. From what I've gathered on following you on Twitter, you're doing just about everything. Did you just start doing this from day one?

[Dr. Venkat Tummala]
I'm an interventional radiologist by training. This is my first job out of fellowship. I've been in practice for nine years. Very fortunate to be a part of a high-end IR practice. We cover five hospitals in the county. The way I got involved with Inari goes back a couple of years. I came from the same thought process of thrombolysis first back in the day in fellowship and kept on doing the same. A couple of cases in a short period of time ended up having an intracranial bleed from CDT and fairly young patients. One of them was a 36-year-old young female with two kids, a mother. That got us thinking a bit, if something that we don't have control on, especially the side effects from a tPA, and the moment Inari came out, we tried a bit with Penumbra for massive and sub-massive PEs. Wasn't really satisfying as far as the clot haul, so we tried Inari, got our feet wet. There is definitely a learning curve but so far we've probably done 60 cases of Inari successfully.

(1) Indications for Endovascular Treatment of Pulmonary Embolism

[Dr. Michael Barraza]
All right. Right on. Yeah, me personally, I'm in Nashville and I didn't do much PE work in training, but I cover eight different hospitals and in some of them we do it. Some of them interventional cardiology does it and some vascular surgeries, a unique mix. But we're still doing primarily catheter-directed thrombolysis, but we have recently gotten the FlowTriever approved. I'm looking forward to giving that a go. Let's talk first about why and when. I'm curious to see what are your personal indications for treating these patients endovascularly. It doesn't have to be, necessarily, strict criteria, but what are you guys recommending or treating these patients?

[Dr. Thomas Tu]
I'll start. I think most of the listeners are familiar with the standard risk stratification for pulmonary embolism, sorting out patients between massive intermediate risk or sub-massive and then low-risk patients. A lot of that has to do with presence or absence of RV strain as well as biomarker positivity and then presence or absence of cardiogenic shock. I think that that framework is commonly used and I think it's useful in identifying very grossly who's at short-term risk of mortality from PE. I think it's got a lot of shortcomings, though. I mean, the whole concept of risk stratification is designed to draw some kind of line over which you say the risk of the disease is higher than the risk of the therapy and below which you say, "Well, maybe it's safer to treat conservatively because the risk of the therapy is too high."

And those lines are drawn mostly based on systemic thrombolysis, which is, up until recently the only approved therapy for pulmonary embolism, and I think as we get safer and safer therapies, more effective therapies, we're going to see the risk stratification change according to a newer and safer way of doing things, very similar to how the treatment of myocardial infarction and stroke is evolving.

[Dr. Michael Barraza]
Sure, yeah. And I'm with you. It sometimes seems like some of the lines are blurred and there are certain things that come in that are outside of the risk stratification, especially in postoperative patients. What about you, Venkat? When are you treating these patients?

[Dr. Venkat Tummala]
I should say from the hospital setting, we've got a robust machine as far as referrals for PE. As a matter of fact, IR was involved with ER physicians and pulmonary critical care doctors from the get-go. We ended up getting a call from the ER physician right off the bat, even before an ICU consult happens and some of our diagnostic partners, they do a pretty good job about giving them a direction. Part of the reporting process for us involves the RV/LV ratio and the location of the clot. And I think that kind of guides the ER together with the clinical picture. They give us a call first and then our paradigm is, "Is it massive or sub-massive?" And if it’s massive, it's emergent, we take the patient straightaway to the lab. If it's sub-massive, I'm with Tom. The literature is all over the place, but we do want to risk stratifying it based on troponins and biomarkers, BNP.

If they are positive and the CT has a significant right heart strain, then we are more likely to intervene and whether it's going to be thrombolysis or thrombectomy, the more we are doing thrombectomy and the results we are seeing on the table with a significant drop in physiological pressures and clot reduction, the paradigm shift is happening, if it's not already towards thrombectomy in this subset of patients.

[Dr. Thomas Tu]
I really think it comes down to the goals of therapy. Predominantly the goal for therapy has been a reduction in short-term mortality, so we've been trying to identify who's at high risk of dying and can we intervene in that subgroup? However, I think as we learn more about PE, we're having additional considerations that we have to account for. For instance, there is the acuity of PE. Someone who may not have a high chance of dying but may end up in the ICU for several days, may end up taking weeks to recover. If we can reduce that person's short-term acuity by allowing them to de escalate, allow them to be discharged from the hospital faster, recover faster, that could also be a goal for therapy.

And then there's also the long-term considerations of somebody who has a large clot burden. We know that all doesn't lyse completely either with endogenous fibrinolysis or exogenous therapies. What happens to that clot over time is that it becomes collagen laden. It transforms to elastin. It develops its own blood supply. It starts secreting hormones. And the way the body deals with chronic thrombus is to incorporate it into the wall of the pulmonary artery as opposed to this hope that it just lyses completely. And if that's a process that leads to CTEPH or some smaller form of that like CTED, I think hopefully we can reduce that incidence as well with more aggressive therapy. Now, we have to gather data and prove that, but that would be the hope.

[Dr. Venkat Tummala]
Right on, Tom. If you look at the clot that's retrieved, right? In my experience the majority of them look like an organized thrombus. And it amazes me. We do tPA, which we know with clots predominantly that are organized, tPA may not work, but when a patient presents to the ER with an acute PE, the DVT that probably provoked the PE is probably an organized thrombus more often than not. And the more we are doing this and the more clot we retrieve and evaluate, it's shocking to see those long threads of organized thrombus. And I started believing in the efficacy of the treatment once I received direct feedback from the patients on the table sometimes: "I can breathe a whole lot better. I haven't breathed like this in 20 years." Those sort of things and supporting evidence with arterial pressures and subsequent follow-up echocardiogram to see resolution of right heart strain. This seems very promising.

(2) Endovascular Treatment Modalities for Pulmonary Embolism

[Dr. Michael Barraza]
Let's get into for a second the endovascular treatment options for PE. We've got catheter-directed thrombolysis. We've got EKOS. We've got thrombectomy and then of course open options like surgical embolectomy. What do you think is the role for tPA now, either systemically or with a catheter when you've got all of these options available?

[Dr. Thomas Tu]
Yeah, that's a great question. There's so many different ways that we can treat pulmonary embolism and this is an interventional-based media, so I assume that your listeners are focused on catheter-directed therapies. But I think it's important to take a step back and recognize that over 90% of significant PEs, intermediate or high-risk PEs, are still treated just with anticoagulation and transition to oral therapies. So I think there's a long way to go just in offering advanced therapies to patients who are currently being treated just with anticoagulation.
When we get into catheter-based therapies or more advanced therapies, I think the way you broke it down is quite helpful. You have the lytic-based therapies, whether that's systemic or catheter-directed and then you have the non-lytic based therapies, which I would say mechanical thrombectomy with FlowTriever is a major component of that, as well as surgery. And it really comes down to, I think, how quickly you need to remove the clot and restore RV function, how effectively you think lytics or going to work versus mechanical thrombectomy and then what risk you want to expose the patient to. And for me, I think having treated hundreds of patients in my career with catheter-directed lytics, I've been burned once or twice. It's not a very common event, but certainly those events stick with you, especially if you were giving catheter-directed lysis for something that wasn't a very mortal disease, you remember every time that you've inadvertently given somebody an intracranial hemorrhage.

If you look at the evolution of treatment for myocardial infarction and stroke where there was an initial interest in lytics and then that kind of faded once we had more effective non-lytic based catheter therapies, I think you'll see PE move in that same direction.

[Dr. Venkat Tummala]
Undoubtedly massive PE, we all agree, right, the patient gets a bolus of systemic tPA, weight based, but more and more we are doing thrombectomy for clot reduction in spite of patients on a full-dose tPA on board. And the reason is very simple, just like in stroke therapies. Although we're comparing apples to oranges here, it's like a large vessel occlusion and the tPA may or may not effectively decrease the clot burden. So we are supplementing that in massive patients with thrombectomy and the results are promising so far. Surgical embolectomy? I have yet to see one in my nine years of practice, I haven't had a CT surgery consulted for a surgical embolectomy. When we move onto the sub-massive population toward what Tom was saying, as well as CDT versus mechanical thrombectomy, I do favor mechanical thrombectomy with avoiding the risk of intracranial hemorrhage that goes with CDT. And, like Tom, I have been burned a couple of times too.

On the other hand, the clot location helps me decide in ways which ones I want to be aggressive with thrombectomy versus CDT. The central, the huge clot burden favors mechanical versus something very segmental or subsegmental PE with the right indication to treat, then that might be something I would consider CDT.

[Dr. Thomas Tu]
Yeah, I would second that completely. The first point is that surgical thrombectomy for pulmonary embolism is a very good surgery. It's not very complicated. It is quite successful in removing large clots, especially big saddle pulmonary emboli. There's two big problems with it, however. One is it's hard to find surgeons who are very enthusiastic about it. In fact, the opposite is true. Once you have a good catheter-based therapy, the surgeons are more than happy to let the catheter physicians treat this disease state. I think one is a reluctance to expose these patients to the risks of major chest surgery and cardiopulmonary bypass. And I think the second is we live in a world now with public reporting. Surgical outcomes are very scrutinized and so surgeons are quite concerned about the possibility of taking these patients who have very, very sick right ventricles and exposing them to the risk of a major chest operation. I do know there are some surgeons who do an excellent job with this, but I think there are quite few.

The second point that Venkat made, I want to reiterate, which is I really think right now the technology is focused on large central clot burdens. So speaking of Inari FlowTriever specifically, I think it's very effective for main PA, right and left main PA, interlobar arteries and maybe out to the basal trunk. I think that's really where we see the best effect and the best technical success. If the clot is beyond that in the segments and the subsegmental areas and you still feel that it's important to treat, I think catheter-directed thrombolysis is very reasonable in those cases.

(3) FlowTriever Pre-Procedural Evaluation

[Dr. Michael Barraza]
As I said, I'm not currently using the FlowTriever but we recently got it approved so for me it would be really helpful to have you guys walk me through the equipment and a case. And one thing I want to start with is when you're doing these, are you doing these under moderate sedation or anesthesia?

[Dr. Thomas Tu]
I'll tackle the first. The pre-procedure assessment of a patient getting a percutaneous thrombectomy I think is critical. It's important to understand what their respiratory and cardiovascular status is so you know the preparation that this patient might need, such as intubation or pressers or some assistance from cardiology or surgery with mechanical circulatory support. So being aware of that up-front and getting the team ready is critical, understanding their anticoagulation or thrombolysis status so you know what the risk of bleeding, particularly with wire perforation as we do do some kind of wire manipulation in the pulmonary arteries, so it's important to understand the risks.

And I think the physiology of the patient undergoing a pulmonary embolism is that they have acute RV strain and the RV is something that is not used to doing a lot of extra work. It can fail unexpectedly. You're very preload dependent and your adrenaline state is high and so routine administration of general anesthesia in intubation is actually not recommended. In this patient population, you can immediately crash and get hypotensive if you give these patients propofol, if you give them high-dose fentanyl, typical drugs that an anesthesiologist might give for induction of anesthesia. We try to avoid general anesthesia and intubation if at all possible.

Now that being said, there are patients with pulmonary embolism who have to be intubated for respiratory support and if we know that's the case, we're very aggressive about supporting with pressers. We might bolus with epinephrine as we're inducing anesthesia. We have all the teams on standby ready to go on ECMO if necessary because every now and then you'll have a patient that just completely crashes as soon as you give a little bit of fentanyl or propofol.

[Dr. Michael Barraza]
Let's take a hypothetical patient and, say you've made the decision to treat the patient with a thrombectomy, the patient is prepped and ready to go. I don't know whichever one of you wants to do this, but one thing I was hoping you could do is cover the different components of the FlowTriever set and then explain to me how you do the case.

[Dr. Thomas Tu]
Yeah, Venkat, I'll have you go through that and then I'll add in if necessary.

[Dr. Venkat Tummala]
Sounds good, Tom. One thing I would want to reiterate.

[Dr. Venkat Tummala]
Being in IR and not knowing how to read EKGs... I'm kidding. Not at least the minor details of an EKG. One thing to pay attention to, which has not been infrequent, is to look for a bundle branch block.

[Dr. Venkat Tummala]
If the patient is having a new-onset left bundle branch block, then there are times when either we had a temporary pacer, placed by cardiology before we do thrombectomy. Attention to this would it help when you are thinking of doing mechanical thrombectomy with a 20 or 24 French device. We don't want to end up in a complete heart block. One key thing these days I look into before doing the case.

[Dr. Michael Barraza]
The first PE case I ever did had a bundle branch block. I'm glad you reminded me.

[Dr. Venkat Tummala]
That's got to be stressful.

[Dr. Thomas Tu]
Let me jump in here as the cardiologist on the line just to explain the physiology in more detail. There's of course two bundles of electrical wiring connecting the atrium and the ventricle, the left and the right bundle, and if someone has a pre-existing left bundle branch block, that means their entire conduction system from atrium to ventricle is reliant on the right bundle and the right bundle travels just underneath the septum on the right side. So any catheters that are directed through the right ventricle that bonk into the septum and can induce heart block will then result in complete heart block and asystole. The pre-existing left bundle branch block without a pacemaker in place could be a danger in performing right heart manipulation, so I would recommend that you put a temporary pacemaker in before proceeding with the procedure.

(4) FloTriever Thrombectomy Procedure

[Dr. Venkat Tummala]
As I say, once we decide, I'm 100% in support of what Tom said earlier in regards to sedation. We almost exclusively do them under conscious sedation with the occasional exception of somebody who needs intubation for oxygenation. Femoral approach, primarily, if I'm pursuing FlowTriever, the right common femoral vein, being right-handed, is the access site. I typically start off with a 6-French sheath in the right common femoral vein. I get into the pulmonary artery using a pigtail catheter and a good old technique of the back end of a Benson bent in a curve like a C-shaped curve. The Benson wire never leaves the catheter but I use the Benson to manipulate the pigtail through the right ventricle into the pulmonary artery. And I think that portion of having the pigtail while crossing the right ventricle is paramount when you are using a FlowTriever device, for a very simple reason that you don't want to be coursing between the caudal terminals in the right ventricle. You do want to avoid them.

Once I get up there, I don't really do a power injection, since I have a CTA most of the time, and I just do get a pressure, a pulmonary arterial pressure as baseline. Then I do a hand injection to see where I am in the scheme of things. On a side note, very rarely, you could find yourself in the left atrium through a patent foramen ovale or an ASD, so I like to make sure there's no air bubbles and just confirm intraluminal location within the main pulmonary artery.

Then I switch out to either a Cobra or a Kumpe 100 centimeter long catheter, try to get segmental with the catheter, preferentially the lower lobe segmental arteries. Then we use a 1-cm short floppy super stiff Amplatz so that it's just a centimeter long floppy tip to avoid perforation in the lungs and subsequent hemoptysis and whatnot. Once we have the Amplatz in place, then we use a 22-French Gore DrySeal Sheath in the groin, if you are going with a T20 device. But if you are using a T24 device, you will need a 24-French Gore DrySeal Sheath.

Once we have the sheath, which is about 33 cm long, it's in the intrahepatic IVC, then we track the FlowTriever device by itself, T20. If it's a sharp angulation in the pulmonary arteries, you could use a T16 inside a T20 to track the T20 into the necessary location being the main pulmonary artery. Then we do aspirations. Sometimes all it takes is two or three good aspirations and then cross over to the left lung, do the same over there. Occasionally you may have to take the device out if it's a long piece of clot, it can get trapped in the T20 device.

Then you maintain your wire access, you deflate the valve in the Gold DrySeal and take the T20 device out, retrieve the clot and then reassess the situation. Then we do a repeat pulmonary artery pressure post-thrombectomy and then a power injection for completion's sake to evaluate all the lobar arteries for their patency and whatnot.

[Dr. Thomas Tu]
Venkat, that's an excellent summary of the procedure. I just want to underline a few of the points that you made because I think they're critical for new users. First of all, Inari FlowTriever system is really a toolkit of multiple different tools that you can choose any or all of the combinations of the devices to use. It is billed as a one price per procedure, so feel free to use as many of the tools as you feel necessary to accomplish what you want to do.

We have the aspiration catheters and, as you mentioned, Venkat, the primary aspiration catheters include the Triever-20 as well as the 24. They're very similar catheters. They have the same length. The only difference is in the diameter of the catheter. Obviously the 24 being 24 French, it's larger and therefore you get a lot more aspirational flow. The trade-off is you have to put a 24-French dry seal sheath in the groin as opposed to a 22.

I would mention that about 10% of our users use the internal jugular approach, which is quite acceptable as well, so there might be reasons why you might prefer the neck, although there's some minor technical differences if you choose to go that way.

In terms of the phases of the procedure, access is one. We really urge you to use ultrasound-guided access so that you don't inadvertently puncture the artery into vein and therefore create an AV fistula. Passing through the right heart, I think you did an excellent description of how to do so using a pigtail technique. We urge you not to straighten the pigtail, especially with a Glidewire because you could get under a cord and many people do so putting smaller catheters in the lung without realizing it and you can get away with it with a 6 or 8 French system but with a 20-French system, you will not get away with it. And so it's really important to pass through the right heart safely.

An alternative technique would be to use a balloon-tipped catheter. Many cardiologists are familiar with pulmonary capillary wedge catheters and balloon-tipped Swan is very effective as well and so that would be a second option for you in that regard. And then taking a pulmonary angiogram, doing the aspiration, I would mention that aspiration alone to remove the clot is often effective in about 70% of cases. Most people find that aspiration alone is all that's necessary to achieve the thrombectomy they were looking for. In the 30% of cases where the clot is wall-adherent, then we have the family of Triever disks. These are nitinol disks that are constrained within a catheter, very similar to the Amplatz family of nitinol devices and the idea is you pass this catheter through the clot, you expose a nitinol disk beyond the clot and then withdraw this system back into the Triever catheter so you disrupt the bond between the clot and the wall, making that clot susceptible for aspiration. In about 30% of cases, we find that the Triever disks are used and are effective in that regard.

And then, lastly, is the hemostasis, which there's several techniques, all of which seem to work well, including using figure-of-eight or purse string stitch using a Perclose or pre-close system or just manual compression. Any of those seem to be very effective in hemostasis and we don't see a lot of vascular complications.

(5) Aspiration with the FlowTriever Device

[Dr. Michael Barraza]
One of the questions I had is about the aspiration because I haven't used this device yet. How are you doing the aspiration? Is it with a catheter?

[Dr. Thomas Tu]
I'll take that because that's really one of the great advances of this system. The first FlowTriever system that I used five years ago was primarily disk focused and aspiration was really more of a secondary function of the device and wasn't really optimized. One of the realizations that I had in using the device was that we could greatly improve the aspirational efficiency of the system and I think we saw a dramatic increase in the efficacy of thrombectomy. If you look at the FLARE study which is the IDE study that we did to get FDA approval for this device, we actually did not have any of the advanced thrombectomy systems that we've now gone with. So we have about three or four generations of devices since the initial FLARE study.

The advancements have all been focused on increasing the aspirational efficiency of the device, so the tubes are very flexible to be able to be passed into the pulmonary artery safely, but they're thin walled to maximize the lumen. But they're robust enough to withstand a full negative atmosphere of pressure, so we really have quite a bit of suction at the end of the device. And then it's optimized all the way through, not just the catheter itself, but through the stopcocks, through the side arm tubing, even the syringes are specially designed to have wide mouths to give no pinch points along the way.

And so we see aspirational flow rates of our T24 system as high as about 175 cc per second, so you can imagine there's a quick blast of suction that's applied when we turn the stopcock on. The suction itself is applied through a 60 cc locking syringe. This is something specially made by Inari Medical. We attach it using a quick connect to the back of the catheter and then lock the vacuum into place and then when we want to activate it, we simply turn a stopcock 90 degrees and all the vacuum is applied in an instant. If you have free flow of blood, you'll see the catheter fill within half a second. That's how quickly this suction occurs.

[Dr. Venkat Tummala]
And, Mike, I've got to say, every time you put that clot on the table, you hear screams. People say, "Wow!" That's the best part of the day for most of the techs. They love doing Inari stuff because they see all these long, fancy clots come out. It cheers them up.

(6) Dealing with Residual Clots

[Dr. Michael Barraza]
Well, in terms of clots. I love seeing the pictures. But that brings me to another question about your technical or procedural endpoint. When you've gotten most of the clot, is that one of the things you use to tell you that you're there is that you just get tons of blood through the catheter and no more clot?

[Dr. Venkat Tummala]
I would say, to me, the pressure measurement is an important part of making that decision. The amount of blood loss and the common thinking would be what, 20 or 24 French device, you would be aspirating a ton of blood and that has not been my experience.

[Dr. Venkat Tummala]
I would say an average 200 or 300 cc of blood loss if we go six to eight aspirates. And the next thing would be the clot burden itself. You do a hand injection intermittently to figure out how much relief you got and, finally, you'll see on the hemodynamic parameters--they change rather rapidly on the table. The tachycardia resolving, the blood pressure improving, the oxygen requirements going down. All these things. And, you're right, the important thing is to know when to stop. And these few things go into making a decision on when to stop the thrombectomy.

[Dr. Thomas Tu]
Venkat, you made some very good points. I just want to add one more. If you take an angiogram at the start of the procedure and your patient is cooperative enough and not tachypneic enough that you can get a nice DSA picture, you can really look at the blush, the blood flow extending all the way to the periphery of the lungs. And frequently you'll find huge patches of lung that are under-perfused. And at the end of the procedure, if you feel that you're getting close to stopping, you take another angiogram and all of those segments are now perfused. I think that's a really good indicator that you've done your job. I think one of the least important indicators is complete angiographic perfection. I think it's unlikely that you're going to achieve that. We do feel like we are getting more thrombus out than we have with any other technique, but I'm not sure that a lot of aspiration in order to get perfect-looking pictures is necessary.

(7) Heparin Usage

[Dr. Michael Barraza]
Assuming that there is going to be a little bit of clot left over, when do you allow the patient to resume heparin?

[Dr. Thomas Tu]
That's a great point. I actually don't interrupt the heparin at all.

[Dr. Thomas Tu]
These patients are on anticoagulation as soon as they're diagnosed because we know early administration and achieving therapeutic PTTs is critical in this disease state. I continue it before, during and after the procedure, so these patients are on IV heparin continuously through the procedure. I oftentimes will give a bolus of heparin to achieve an ACT of around 250 seconds. That's to prevent clot forming in these venous catheters. And then because it's just the vein, you can get really good hemostasis without having to worry about reversing the anticoagulation or holding heparin. I personally like the figure-of-eight stitch, so I use that and they stay on IV heparin overnight.

After the procedure, if I feel that they're de-escalated enough that they're in a much better shape, I will oftentimes start them on oral anticoagulation the next day and stop the IV heparin, expediting their throughput through the hospital and oftentimes one side benefit of good thrombectomy is that these patients de-escalate to the point where they don't need to be in the ICU. Frequently, these patients start off a little sick, people are wary, but they get better on the table so they can go to the regular floor afterwards.

[Dr. Venkat Tummala]
I modify it a bit, Tom. For the most part, I agree with you. We bolus them on the table 70 mg/kilo to get them therapeutic while doing the thrombectomy. After the Perclose suture or even a pursestring suture, I give it a two hour break. I give two hours off and then we start IV heparin without a bolus, keeping them anti-coagulated in two hours. And I think there's a time between the heparin bolus administration and restarting the heparin is usually about a couple of hours. I think the bolus helps to cover that two hours, but if it's longer then I may start heparin sooner. But, in general, we give them a two-hour break before restarting it.

(8) FlowTriever Technique

[Dr. Thomas Tu]
I do want to talk a little bit more about the technical aspects of the procedure because I think as a procedural-based specialty, your audience might want to hear some of the other techniques and lessons we've learned over a 4,000-case experience. We did talk about the access, we talked about crossing through the right heart. I do want to mention that all of our systems are over the wire, so you need long wires. Whatever support wire you choose to do this over should be at least 260 or 300 centimeters. I've found that navigating through the pulmonary arteries is safest with a spring coil tipped wire as opposed to a hydrophilic polymer tipped wire, so I might use something like Supercore, Magic Torque or something like that.

The disadvantage of that system is that they oftentimes have longer soft tips, so you won't get support anywhere near the distal 5 or 7 cm of the wire. If you're really trying to get distal support, you'll have to knuckle the wire and place the stiffer part distally. Or, like Venkat suggested, change out for an Amplatz super-stiff 1 cm tip, which is an excellent wire for support, just not one that I would advance without having placed a catheter in the right place prior. I exchange for that wire, I don't advance it on its own.

And then as you advance the catheter through the right heart going through the right atrium, right ventricle, tricuspid valves and make the bend into the right or left main pulmonary artery, there is a little bit of active wire manipulation to either withdraw or relax the wire to get the tip pointed in the right direction and in very dilated right hearts, as Venkat mentioned, but I'll underline, if you're having difficulty, you can use a transitional catheter such as our Triever 16, which is a 16 French system that takes the curve nicely and then you can telescope your catheter into place.

[Dr. Thomas Tu]
The ideal placement of the Triever aspiration catheter is right at the proximal edge of the clot. I recommend that you start aspirating proximally first. That reduces the chance that you're going to push the clot further into the lungs and perhaps cause it to become occlusive and then, if you can aspirate right on the proximal edge, I think you'll have the best luck. If there's a long saddle, oftentimes because the saddle of the pulmonary arteries is quite a large structure and it might be hard to get close enough, that would be the one exception where I actually will try to pull the clot out from the distal end and pull it out backwards. And usually you can snare it around the area of the bifurcation of the truncus anterior and the intralobar artery on the right or around the intralobar artery basal trunk on the left. Those are common locations to grab the clot successfully.

[Dr. Venkat Tummala]
The upper lobar arteries can be challenging, at least in the beginning, to get up there and do a thrombectomy. You may have to add additional wire to provide stability to the device to track up to the upper lobes. But even when you're starting out, I would suggest that stay central, stay in the lower lobes, that's probably where you will have successful outcomes.

[Dr. Thomas Tu]
Just to add to what Venkat said, the truncus anterior on the right is a common place for a clot to reside. You don't always have to go into the truncus to remove the clot because oftentimes the clot will just naturally come out of the truncus when you grab it in the intralobar artery. But if you have to get it out of the truncus, one thing you can do is simply just withdraw the Triever catheter from the intralobar artery on the right and as it gradually starts to point upward, even with the wire in the inferior lobe, you can aspirate the clot that way. If you feel that that's not successful and you have to then insert the Triever catheter into the truncus itself, I would recommend a buddy catheter in which you leave a wire in the inferior lobe for stability, as Venkat mentioned and then you take an angled catheter and direct it up into the truncus and get your access that way.

[Dr. Michael Barraza]
Well, if there's nothing else that you guys would like to cover, I just want to thank you both for joining me on the podcast and diving into this with me. This is an exciting topic and an exciting piece of equipment that I'm looking forward to using. And, of course, I want to thank our sponsor, Inari Medical. The Inari FlowTriever is the first mechanical thrombectomy system indicated for the treatment of PE. Again, we encourage you to go to Inarimedical.com for more information. Thanks again, everybody, for joining us.

Podcast Contributors

Dr. Venkat Tummala

Dr. Venkat Tummala is a practicing interventional radiologist with Lakeland Vascular Institute in Florida.

Dr. Thomas Tu

Dr. Thomas Tu is an interventional cardiologist and chief medical officer of Inari Medical. Until recently, Dr. Tu was the director of the cardiac cath lab at Louisville Cardiology in Kentucky.

Dr. Michael Barraza

Dr. Michael Barraza is a practicing interventional radiologist (and all around great guy) with Radiology Associates in Baton Rouge, LA.

Cite This Podcast

BackTable, LLC (Producer). (2020, March 11). Ep. 58 – Endovascular Treatment of Pulmonary Embolism [Audio podcast]. Retrieved from https://www.backtable.com

Disclaimer: The Materials available on BackTable.com are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.