Key components of successful mechanical thrombectomy include good vascular access, safe passage through the right heart and pulmonary artery, and optimal procedural endpoint. Interventional cardiologist Dr. Thomas Tu and interventional radiologist Dr. Venkat Tummala discuss their experiences using the Inari FlowTriever, providing an overview of the procedure workflow. They also share their tips and tricks on endovascular technique for the removal of thrombus.
We’ve provided the highlight reel below, but you can listen to the full podcast here.
The BackTable Brief
Pre-procedure assessment prior to percutaneous thrombectomy is critical. Anticoagulation, respiratory, and cardiovascular status are all important to consider. Both Dr. Tu and Dr. Tummala try to avoid general anesthesia and intubation if at all possible.
Endovascular access is achieved via the femoral or jugular veins. Dr. Tu recommends ultrasound-guided access to avoid inadvertent punctures, and Dr. Tummula describes his pigtail technique for safely passing through the right heart.
Dr. Tu and Tummala discuss optimizing procedural endpoint; Dr. Tu advises taking a pre and post procedure angiogram to assess perfusion. Dr. Tummala compares pre and post procedure hemodynamic parameters. He takes a repeat pulmonary artery pressure reading and considers total blood loss when determining his procedural endpoint.
An advantage of the FlowTriever system is its high aspiration efficiency and strong suction. In addition, the nitinol Triever disks help retrieve wall-adherent clots.
Image courtesy of Brandon Awalt
Disclaimer: The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.
Using the Inari FlowTriever for Mechanical Thrombectomy, An Overview of the Process
The Inari FlowTriever is the first mechanical thrombectomy system indicated for the treatment of pulmonary embolism. Dr. Tu and Dr. Tummala discuss how they use the Inari FlowTriever System and describe workflow from pre-procedure assessment to safe pulmonary artery access and hemostasis.
As I said, I'm not currently using the FlowTriever, but we recently got it approved. Could you walk me through the equipment and a case?
The pre-procedure assessment of a patient getting a percutaneous thrombectomy is critical. It's important to understand their anticoagulation or thrombolysis status as well as what their respiratory and cardiovascular status is so you know the risks that this patient might need additional support. 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… We try to avoid general anesthesia and intubation if at all possible.
I'm 100% in support of what Tom said earlier about sedation. For the procedure, I typically start off with a 6-French sheath in the right common femoral vein.
I would also mention that about 10% of our users use the internal jugular approach.
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 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. Once I’m there, I don't really do a power injection. Since I have a CTA most of the time, I just get 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 cm 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. 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. 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 in the main pulmonary artery. Then we aspirate. Sometimes all it takes is two or three good aspirations and then I cross over to the left lung, where I do the same thing. Occasionally you may have to take the device out if it's a long piece of clot, as it can get trapped in the T20 device. Then you maintain your wire access and deflate the valve in the Gold DrySeal. Take the T20 device out, retrieve the clot, and then reassess the situation. 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.
Venkat, that's an excellent summary of the procedure. I just want to underline a few more points. 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. Lastly is the hemostasis. There are several techniques—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.
Endovascular Technique for Successful Mechanical Thrombectomy Using the Inari FlowTriever
Dr. Tu and Dr. Tummala discuss techniques for catheter placement and manipulation during mechanical thrombectomy. They also provide indications for when it is appropriate to stop aspirating. According to Dr. Tu, aspiration at the proximal edge of the clot is ideal and taking a pre and post procedure angiogram to assess perfusion will help determine procedure endpoint. For thrombus located in the upper lobar arteries, Dr. Tummala suggests adding additional wire to provide stability to the FlowTriever device. Changes in heart rate, blood pressure, oxygen requirements, and blood loss help Dr. Tummala assess optimal clot retrieval.
As you advance the catheter through the right heart 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, especially in very dilated right hearts. 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. 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.
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.
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 interlobar artery. But if you have to get it out of the truncus, you can withdraw the Triever catheter from the interlobar artery on the right. 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's not successful and you have to then insert the FlowTriever catheter into the truncus itself, I would recommend a buddy catheter in which you leave a wire in the inferior lobe for stability, then take an angled catheter and direct it up into the truncus to get your access.
How do you know when you have retrieved most of the clot? Do you just get tons of blood through the catheter and no more clot?
The pressure measurement, blood loss, and clot burden are all important. 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.
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 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. 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.
Advantages of the Inari FlowTriever for Mechanical Thrombectomy
Dr. Tu discusses advancements in the FlowTriever’s aspiration efficiency as well as the use of Triever nitinol disks for disrupting clots that are wall-adherent.
One of the questions I had is about the aspiration because I haven't used this device yet. How are you doing the aspiration?
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. 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. 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.
I would mention that aspiration alone to remove the clot is often effective in about 70% of cases. 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. The idea is you pass this catheter through the clot, 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.
Dr. Venkat Tummala is a practicing interventional radiologist with Lakeland Vascular Institute in Florida.
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.
Host Dr. Michael Barraza is a practicing interventional radiologist with Radiology Alliance in Nashville.
Cite this podcast:
BackTable, LLC (Producer). (2020, March 11). Ep 58 – Endovascular Treatment of Pulmonary Embolism [Audio podcast]. Retrieved from http://www.backtable.com/podcasts
The Materials available on the BackTable Blog 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.
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