FlowTriever Embolectomy for Acute Pulmonary Embolism

During today’s session dedicated to acute venous thromboembolism, panelist and speaker Gary Ansel (Columbus, United States) discussed discuss the FlowTriever System (Inari Medical) – the first mechanical thrombectomy device indicated for the treatment of pulmonary embolism (PE). 

Speaking to LINC Today, Dr Ansel introduced the device, its benefits, and gave a glimpse of some of the key considerations he shared with the LINC audience. 

Am I right in saying the FlowTriever system is the first mechanical thrombectomy system for PE? What are some of the unique characteristics important to highlight? 

The FlowTriever system is certainly the first system that went beyond the application of thrombolysis, or pure aspiration, for the treatment of PE. Full-dose thrombolysis and even limited-dose thrombolysis via catheter were associated with a risk of bleeding, and I feel that this led to guidelines limiting aggressiveness in the treatment of PE.

Rheolytic thrombectomy was one of the first aspiration-based procedures, but it was associated with arrhythmia and significant hemolysis. The risks seemed to outweigh the benefits and its use received a Food and Drug Administration black-box warning in the United States. What’s more, smaller-French aspiration devices were not very efficient and had significant blood loss.

There’s always a fine line to navigate between enough clot removal and blood loss. The Angiovac from Vortex was the first large-lumen aspiration catheter, but it was not able to be manipulated beyond the main pulmonary artery. It did auto-transfuse the patient, which allowed for minimum blood loss, but required a centrifugal pump system.

The FlowTriever system from Inari was a big technological step forward, offering improved flexibility and allowing for the advancement of the large-bore main system. Furthermore, it incorporated collapsible baskets to facilitate the removal of the pulmonary emboli with a more organized thrombus, and allowed for the operator to create improved aspiration due to a unique larger-bore syringe and attachment. 

Large blood loss with the FlowTriever system was an initial shortcoming, but that has now been addressed with the addition of the FlowSaver component. The initial Inari system allowed for the swift, effective treatment of large pulmonary emboli and typically, an "on-table" result that could be utilized by a broader base of practitioners. It changed our institution's approach to the treatment of PE from a lytic-based to a mechanical-removal-based approach.

Can you briefly run through the specifics of the clot removal process?

Using a brief description: venous access is obtained, typically with ultrasound guidance, either at the common femoral or jugular venous site. Most commonly, a balloon-tipped catheter is used to keep the initial wire out of the tricuspid valve chordae, although .035 wire placement into the pulmonary vasculature may be accomplished with various catheters. 

A large-bore sheath is then positioned. The main FlowTriever aspiration catheter is placed over the wire and then the FlowTriever main device (of which there are multiple generations) is chosen and advanced to the main pulmonary artery. Optimal placement for the large-bore catheter is just proximal to the beginning of the clot. Aspiration is then started with the large-bore syringe. The blood and clot combination is aspirated and then filtered to allow for the replacement of the removed blood component. 

On occasion, the clot will occlude the catheter, and flow ceases. If this occurs, the catheter is slowly withdrawn (while leaving the wire in place) and externalized. This is often quite successful in removing a very large clot. Pulmonary angiography is easily completed with dilute contrast to assess the result, and the procedure is then repeated in the same fashion in other areas if needed. Finally, the access site may be addressed with a figure-of-eight soft-tissue suture technique.

Then, if the clot persists, do you use the FlowTriever catheter mesh discs (of various sizes) to engage the clot and pull it back through? Tell us more about this technology.

If, after several attempts at aspiration, there is a stubborn area of PE, then the mesh discs are used to attempt the removal of the wall-adherent clot. These cases are typically a mixture of acute or chronic PE, and the chronic component may be associated with wall adherence. 

The basket technology can be of some assistance, especially in the left lower lobe where the angle can be suboptimal for the large-bore catheter to pass over the clot, and the baskets can often assist in moving the embolus to a more favorable position. However, it’s surprising how often the mesh discs are not needed for a successful procedure, especially when using larger-French devices. 

What are some of the core benefits associated with this system? 

In my opinion, the Inari FlowTriever system has helped usher in a new paradigm of effective treatment for clinically significant PE. In my previous institution's experience, the device is typically a single-session treatment, and this has now been borne out in trials. 

Very often, sick patients would become hemodynamically, clinically, and symptomatically stable, before one’s very eyes. This was the finding in the recently presented FLAME trial, where patients with high-risk, massive PE were treated with FlowTriever and had remarkably low mortality. To have a patient express their gratitude during the actual procedure and say that they can breathe normally again is wonderful.

The lack of apparent need for thrombolytic therapy in the majority of these patients is a huge step forward for several reasons. The traditional use of thrombolytics via catheter-directed thrombolysis for this process was difficult for the patient, as they often had to lay flat in an ICU bed with persistent symptoms. It’s also tough for the allied health team in the ICU, and the physician. Both groups disliked the traditional treatments due to the delay in improvement and bleeding risks. 

Many patients with PE who have contraindications to thrombolysis, such as recent surgery or an underlying cancer diagnosis, could not even be offered thrombolysis due to bleeding risk. And in the United States, there’s a significant legal risk with thrombolysis use as well. 

The other potential core benefit of effective mechanical thrombectomy appears to be cost. Though the treatment is expensive, it typically does not require an ICU bed and often reduces the number of in-patient hospital days, so it can be more cost-effective than thrombolysis. 

Will you be talking about the FlowSaver component as well, i.e. blood loss?

Yes, the FlowSaver component is an important advancement in the treatment of PE with FlowTriever, as it allows for the replacement of the removed blood and a low rate of hemolysis. Replacement of the blood loss now allows physicians to define the end of the procedure more clearly, based on clot removal, instead of trying to balance clot removal and blood loss. 

Are there any challenges, limitations, or device iterations that you will be focusing on?

My experience managing various specialities and levels of hospitals in the Ohio Health System has given me a unique perspective on the challenges of large-bore catheter use for PE treatment. 

I’d like to point out that Inari has quickly improved many of the early limitations of the FlowTriever device. It has also added to the literature on the treatment of PE and funded clinical trials. Randomized trials with the FlowTriever device are important to help us compare it to the currently enrolling HI-PEITHO Trial. As complications associated with PE treatment are hopefully lowered, we may see a broadening of indications for treatment beyond the simple mortality statistics that the traditional guidelines focus on.

One of the ongoing limitations of the FlowTriever procedure, or any device treatment, is being able to safely navigate through the right heart. Though cardiologists frequently navigate the pulmonary vasculature and are comfortable with arrhythmia treatment (due to this experience, clinically significant arrhythmia is seen infrequently), this has to be more formally addressed because of the other specialities now performing PE treatment. 

There is also a skill set for safe wire placement into the distal pulmonary vasculature. A perforation here can be devastating, especially if perforation treatment is not in the skill set of the institution. 

I do think there is a difference in using advanced devices in community hospitals vs tertiary care hospitals. As for acute myocardial infarction (STEMI), even though PE is frequently diagnosed in community hospitals, we need to demonstrate that the low risk evident in trials can be transferred to use in community hospitals – especially since many of these procedures are completed with a company representative resource present. Most advanced interventional treatment success is often facilitated by an expert hospital support staff. 

Let’s look at the device’s development. The first generation of FlowTriever was somewhat stiff and could be difficult to place, especially in the left lower lobe vasculature and in patients with significant right heart dilation. Inari addressed these issues with a span of 16-, 20-, and 24Fr systems, as well as improvements in flexibility and shaped catheter designs. Again, with increasing French-device size, there was a transition to more aspiration and less disc retrieval. The early blood loss before FlowSaver was a real problem, and has been addressed as well. 

One of the other limitations is trying to balance the desire to do other interventional procedures with the expertise required for treating the broader disease process. There are increasing physician shortages in many specialities around the world. Providing the level of expertise needed for the advanced treatment of PE has to be balanced with the desire of various physicians to add another treatment to their skill set.

In our system, there were and are interventional cardiologists who wanted to start performing the FlowTriever procedure that do not routinely treat the various levels of PE associated with deep vein thrombosis and clotting disorders. Yes, they may be able to do a FlowTriever procedure, but is this optimal for that patient? 

We also had vascular surgeons and radiologists at some of the smaller institutions that were not comfortable with manipulating large-bore catheters through the right heart. So, while the FlowTriever system is a big step forward in the treatment of PE, there are many environments where smaller diameter aspiration or thrombolytic devices may be more suitable.

For the LINC audience, what’s your take-home message on FlowTriever and the arena of embolectomy for acute PE?

The Inari FlowTriever system is the first truly mechanical thrombectomy system to offer reliable on-table PE clot removal. The system continues to be improved, both in terms of usability and clinical efficacy, and should be considered by all health care systems offering advanced PE treatments regularly. Institutional experience, support systems, and outcomes will be important in evaluating whether the FlowTriever system is optimal for their environment. Ongoing research, especially randomized trials, will be important, as more devices become available to successfully treat PE.