Mechanical extraction of chronic venous thrombus using a novel device: a report of two cases

In deep vein thrombosis (DVT), the structure and composition of the venous thrombus can change rapidly over time. Studies have shown mixed results with anticoagulant and thrombolytic therapies, and the issue will be exacerbated in the case of chronic DVT (defined as thrombus still present after ≥4 weeks of failed treatment after a DVT diagnosis), with no well-accepted interventions. In the present report, we have described two patients in whom mechanical thrombectomy with a novel device was used to remove extensive, chronic thrombus. At follow-up, both patients showed improved blood flow and patency with resolution of their edema and pain. Because thrombus can often be more chronic than expected from a patient’s medical history alone, mechanical intervention as the first approach might be warranted.

The thrombus composition in patients with deep vein thrombosis (DVT) is everchanging. Within 3 weeks of the initial formation, the thrombus could be composed of #80% collagen. 1 As this structural transformation progresses, thrombolytic efficacy will deteriorate because thrombolytic drugs cannot dissolve or break up chronic, collagenous material. Consequently, three major clinical studies of patients with DVT had constrained inclusion criteria that limited patients to those with symptoms for <14 days (ATTRACT [acute venous thrombosis: thrombus removal with adjunctive catheter-directed thrombolysis], 2 CAVA [ultrasound-accelerated catheterdirected thrombolysis on preventing post-thrombotic syndrome] 3 ) or <21 days (CaVenT [catheter-directed venous thrombolysis in acute iliofemoral vein thrombosis] 4 ). Thus, the real-world applicability of these studies has also been limited. However, a mechanical device that does not require adjunctive thrombolytic agents would bypass these limitations.
The ClotTriever System (Inari Medical, Irvine, CA) is a mechanical thrombectomy device and has been shown to be effective in successfully removing thrombus from acute, subacute, and chronic lesions. 5,6 A comprehensive review of the literature revealed a limited but growing body of reported studies on the use of mechanical thrombectomy to treat chronic DVT. Dexter et al 5 reported that mechanical thrombectomy resulted in positive thrombus removal, procedural outcomes, and safety outcomes at 30 days that were sustained in the longterm outcomes at 6 months. Maldonado et al 6 showed that although 49.0% of extracted thrombus was more chronic than the patient symptom duration had suggested, mechanical thrombectomy was effective in removing thrombus of all chronicities. Mouawad 7 reported the case of a patient with chronic thrombus who had experienced complete resolution of decadeslong ulceration and avoided amputation after successful treatment with mechanical thrombectomy, demonstrating the promise of this procedure.
The ClotTriever BOLD catheter (Inari Medical) is an addition to the system, with a more robust coring element designed for more intractable and chronic thrombus. The device has a stronger radial force, is slightly more aggressive, and could be one of the tools used to treat chronic thrombus. To the best of our knowledge, the present report is the first of this novel device. We have reported the outcomes of two patients with chronic thrombus in whom anticoagulation therapy or thrombolytic agents, or both, had failed. We have also elaborated on the underlying pathophysiology to assist physician decision-making. The patients provided written informed consent for the report of their case details and imaging studies.  One of the paired right posterior tibial veins was accessed and venography performed, revealing that the popliteal vein was completely occluded with thrombus proximally. The femoral vein was occluded distally, and the right EIV was patent with nonocclusive, wall-adherent chronic thrombus (Fig 1, A). Overnight lysis was initiated.
The EKOS catheter was removed the next day, and venography showed improvement but with persistent areas of narrowing and chronic thrombus. The right femoropopliteal segment had residual chronic thrombus throughout, with flow-limiting synechiae, webbing, and multiple areas of tight narrowing (Fig 1, B). Given  advanced through the sheath, deployed in the IVC, and then retracted (Fig 1, C), collecting and extracting dense, chronic thrombus in five passes (Fig 1, E). Repeat venography demonstrated significant improvement in the right femoropopliteal segment with some mild residual narrowing. After 10-mm balloon dilatation, the segment was widely patent with antegrade flow and no significant residual collateral flow (Fig 1, D). The patient presented for IVC filter removal 7 weeks after discharge and was found to have bilateral lower extremity swelling.
An initial venogram demonstrated chronic occlusion extending from the bilateral CFVs to the bilateral CIVs and to below the IVC filter (Fig 2, A), prompting a decision to reschedule the procedure to allow planning for thrombectomy with the ClotTriever system. The patient returned 3 weeks later for outpatient IVC filter removal, recanalization of the iliocaval segments via mechanical thrombectomy, and possible placement of a Food and Drug Administrationapproved stent in the chronically occluded segments.
The patient was placed supine, and the right internal jugular vein was accessed under ultrasound guidance. A CT venogram Recanalization was performed from the bilateral CFV access owing to its proximity to the location of the thrombosis and to ensure increased support when crossing highly organized thrombus. Access to the right CFV was achieved using ultrasound guidance with a 19-gauge needle. A guidewire (Glidewire Advantage; Terumo Interventional Systems, Tokyo, Japan) was advanced within the CFV. The tract was dilated, and a 10F sheath was advanced into the proximal CFV. Recanalization was performed using a 5F catheter and guidewire. The same steps were repeated to access and recanalize the left CFV (Fig 2, B). A 14-mm balloon was used to perform angioplasty of the IVC, with a 12-mm balloon used for the right and left CIVs, and a 10-mm balloon used for the CFV. After serial dilation, a 16F Clot-Triever sheath was advanced into the right CFV and a 13F ClotTriever sheath into the left CFV. A ClotTriever BOLD catheter was advanced beyond the thrombus, expanded into the vessel, and retracted. Four passes were made on each side, yielding significant amounts of chronic-appearing thrombus (Fig 2, F). Venography performed after thrombectomy demonstrated restored IVC patency (Fig 2, C). Intravascular ultrasound confirmed that the infrarenal IVC was free of thrombus. Two 14-mm Â 140-cm stents (Zilver Vena; Cook Medical Inc, Bloomington, IN) were placed into the bilateral CIVs. Venoplasty was performed before and after placement.
Final digital subtraction angiography demonstrated restored patency and flow into the bilateral CIVs and IVC (Fig 2, D). After the procedure, a CT scan demonstrated patent bilateral CFVs (Fig 2, E). All catheters and wires were removed. Hemostasis was achieved by manual compression. The total procedure time was w3 hours, and the total device time was w45 minutes. The patient was discharged the same day.  Increasing evidence has suggested that the extracted thrombus will often be older and more chronic than the DVT symptoms would suggest. 6,7 The outcomes from the ClotTriever Outcomes registry have shown that w50% of patients will have thrombus that is more chronic than that determined by the symptom assessment alone. 6 In the present case series, the initial course of treatmentdcatheter-directed thrombolysis for patient 1 and anticoagulation therapy for patient 2dhad done little to dissolve the thrombus or prevent it from evolving into more collagenous material. The structural transformation had progressed beyond the ability of these treatments to have any meaningful effects on the acute or long-term outcomes. A recent study reported that despite patients having an acute onset of symptoms, 91.7% of the thrombi were classified as "old" or chronic via magnetic resonance venography. As a treatment of DVT, catheter-directed thrombolysis was found to have failed a significant proportion of the time, with a success rate of only 57.1%, which had decreased precipitously to 16.7% for old, or chronic, DVT. 8 Additionally, major bleeding had occurred in 5.4% of the patients. 8 For our two patients, a mechanical thrombectomy solution was able to extract nearly all of the thrombus, regardless of its age or chronicity. The device selected was designed for improved thrombus engagement, with a greater radial force and better wall apposition than its predecessor. For patient 1, extensive chronic material had been extracted after multiple passes with the ClotTriever BOLD catheter, completely restoring flow through the previously occluded femoralepopliteal segment. For patient 2, complete clearance of the IVC allowed the operator to forgo the need to stent those segments. These results have shown that mechanical thrombectomy with the ClotTriever BOLD catheter could be a viable solution to treat chronic DVT proximal to the popliteal vein.