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BackTable / VI / Article
Clot in Transit: Definition, Diagnosis & Decision Making
Caleb Solivio • Updated Jun 19, 2023 • 328 hits
Clot in transit, also called ‘free-floating clot’, is a broad term that refers to thrombus that is adherent to structures within the body. If dislodged, they can pose a significant risk to patients’ health due to their potential to embolize other vessels or organs in the body. Though clot in transit can be found using different forms of imaging, they are often found incidentally and in conjunction with other conditions, making their management difficult. Dr. Rehan Quadri, an interventional radiologist at UT Southwestern, calls upon his experiences as a new attending to delineate a framework for diagnosing and treating clot in transit. This article features excerpts from an episode of the BackTable Vascular & Interventional Podcast. You can also listen to the full podcast below.
The BackTable Brief
• ‘Clot in transit’, also known as ‘free-floating clot', is an umbrella term that refers to thrombus that is partially attached to something in the body; that can mean the wall of a vein, valve, atria, catheter, or device.
• Mortality rates from clot in transit are reported in the literature at about 29%, but can be up to 40% depending on the size of the clot and presence or absence of clot in the lungs.
• On echocardiogram, clot in transit commonly appears as an ‘echogenic mobile density’ in one of the heart chambers. CTA can also be used to visualize clot in transit, but it requires a precise venous phase, which can further necessitate the use of echo.
• Two common concomitant conditions with clot in transit include PE and catheter malfunction. When removed from the body, histopathological examination of clot in transit reveals a mix of acute and chronic components.
Table of Contents
(1) Defining Clot in Transit
(2) Detection and Diagnosis of Clot in Transit
(3) Integration of Clot in Transit into Existing Treatment Algorithms
Defining Clot in Transit
The typical presentation of clot in transit, also known as a ‘free-floating clot’, is thrombus bouncing around in the right atrium or right ventricle waiting to move into the pulmonary artery. However, the terminology ‘clot in transit’ is quite nebulous, given its variable presentation as a clot that's partially adherent to the wall of a vein, valve, atria, catheter, or device. Existing papers report mortality rates with clot in transit to be about 29%, depending on their size and the existence of clot in the lungs or not, mortality rates can be up to 30 or 40%.
[Dr. Michael Barraza]
Let's talk about clot in transit. I know you guys are doing a lot of thrombectomy-type work for DVT, PE. Let me just start by saying, what the hell is clot in transit, Rehan?
[Dr. Rehan Quadri]
The definition is rather vague. Traditionally, what you think about in the worst-case scenario is the washing machine clot. There's a piece of clot that's in the RA or in the RV and it's just bouncing around and the next step is to go to the PA. Depending upon what the size it is and depending upon if they already have clot in the lungs or not, the mortality can be up to 30% to 40%.
[Dr. Michael Barraza]
Wow.
[Dr. Rehan Quadri]
Most papers will quote it at 29%, some will quote it at higher than that. It's something that generally has been thought of as an emergent problem. Then there's also the notion of clot in transit being something that's partially adherent, whether it's to the wall of the vein, whether it's to the valve, to the atrial wall, or to the most common thing we see as a catheter or device pacer leads, different kinds of things like that - particularly dialysis catheters. Some people call it clot in transit or they'll use the term free-floating thrombus.
[Dr. Michael Barraza]
Yes, I've heard that more frequently and clot in transit, I'm starting to hear more about it now.
[Dr. Rehan Quadri]
Yes. Traditionally, they say it's supposed to be in the RA or in the heart, but it can actually be in the cava, but it's very rare that you would catch it in the cava because at that point, it'd probably end up in the cardiac chambers.
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Detection and Diagnosis of Clot in Transit
Dr. Rehan Quadri states that echocardiogram is the most common diagnostic tool for clot in transit, but also posits that clot in transit is often an incidental finding during the assessment of a pulmonary embolism (PE). It appears as an ‘echogenic mobile density’ in one of the heart chambers. Clot in transit can also be visualized on CTA, but it requires obtaining a precise venous phase which can be challenging and often necessitates further confirmation via echo.
[Dr. Michael Barraza]
Okay. How is it traditionally diagnosed?
[Dr. Rehan Quadri]
I would say the most common is echo and not infrequently it's a finding on an echo when you're trying to categorize a PE and when they get the transthoracic echo, they'll notice in the RA that there is a, they'll call it an echogenic mobile density. The other time you see it is incidentally on CTAs, and then I haven't really seen it diagnosed. I'm sure this happens, but at the time of a pulmonary embolectomy/thrombectomy, I'm sure they see it on that as well.
[Dr. Michael Barraza]
Sure. I was going to ask you when you look for it, but in most circumstances when you're dealing with a heavy clot burden with pulmonary emboli, you're going to be getting an echo anyway, right? Or do you ever specifically go about looking for clot in transit?
[Dr. Rehan Quadri]
For most of our PE cases - so we've done about 13 clot-in-transit cases total. Because we see it a lot in the Parkland population and also in the Clements population, it is something that the cardiologists look for more when we get echos in the setting of PE, but a common reason that we've had in our case series is actually catheter malfunction. Then we'll get an X-ray, and then they'll do a venogram potentially or they've exchanged the catheter a couple of times, not sure what's going on. Somebody will get a CTV or CTA because in a combination with the catheter malfunction, they have SVC syndrome-like similar symptoms, swelling.
Then you end up seeing it on the CTA, which is hard because you really have to get a good venous phase, and that timing is difficult. So, then you end up getting an echo to really confirm it.
Integration of Clot in Transit into Existing Treatment Algorithms
Diagnosis and treatment of clot in transit can be nuanced by concomitant PE or issues with dialysis catheters. Consequently, the approach to treating clot in transit may be two-fold, focusing on the clot in transit itself and creating a management strategy for the PE or problematic device. As opposed to PEs, which typically demonstrate an acute pathological makeup, clot in transit demonstrates a mixed composition of acute and chronic components, raising questions about their disease progression.
[Dr. Michael Barraza]
How does this factor into your treatment algorithm for treating PEs or other venous thromboembolism conditions where you're going to be thinking about doing a thrombectomy? Are you ever going in and just treating the clot in transit or is it typically in conjunction with the treatment of a PE?
[Dr. Rehan Quadri]
It's both. The first case we did, the patient actually had a dialysis catheter and they had about what measured 2.8 centimeters on the transthoracic echo. It was basically like a lollipop clot coming off and it was connected to a fibrin sheath, but that wasn't apparent on the echo. They just saw the clot bouncing around in the RA. They called it a clot in transit and they did have PE. The PEs were relatively small and peripheral, but their problem was recurrent PE, malfunction of the catheter, and at instances, the catheter getting infected frequently.
In that setting, we went in, took out the clot in transit, but the PE being relatively small and peripheral, we didn't actually go for it. Actually, the PE resolved with heparinization.
[Dr. Michael Barraza]
Yes, it makes sense. You don't want a 2.8-centimeter clot going through in the pulmonary arteries. That's going to be, in normal size PA, it's going to be occlusive.
[Dr. Rehan Quadri]
Yes, basically. Across the spectrum, the one thing I've learned is people rip out catheters all the time and fibrin sheets are probably left there. Does it matter in most cases? People say no, but honestly, we don't really know in a lot of instances. You don't necessarily see that person come back to your institution for the problem or different things. We're just trying to figure that process out. We send a lot of the clots for path[ology] as well.
[Dr. Michael Barraza]
Do you?
[Dr. Rehan Quadri]
Yes, so almost all of them are mixed.
[Dr. Michael Barraza]
For clot in transit or the PE as well?
[Dr. Rehan Quadri]
The PE is usually acute, and then the clot transit is usually mixed.
[Dr. Michael Barraza]
That's very interesting.
[Dr. Rehan Quadri]
It'll harbor there for a while. The mixed part sometimes is that the entirety of the clot is chronic, and then there's a small piece that's acute. Or it's like the distribution is hard to get when we send the path, but they generally will say, yes, there's more than just acute stuff. They'll say there's fibrin basically, there's organization to it.
Podcast Contributors
Dr. Rehan Quadri
Dr. Rehan Quadri is a practicing interventional radiologist and an Assistant Professor in the Vascular Interventional Radiology division of the UT Southwestern.
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). (2023, February 6). Ep. 289 – Treating Clot in Transit [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.
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