Histopathologic analysis of extracted thrombi from deep venous thrombosis and pulmonary embolism: Mechanisms and timing

In Vivo Porcine Model of Acute Iliocaval Deep Vein Thrombosis

CLINICAL IMPACT

The study establishes a rapid, technically straightforward, and reproducible porcine large animal model for acute iliocaval deep vein thrombosis (DVT). The procedure can be performed with basic endovascular skillsets. With its procedural efficiency and consistency, the platform is promising for comparative in vivo testing of venous thrombectomy devices in a living host, and for future verification and validation studies to determine efficacy of novel thrombectomy devices relative to predicates.

Single-center experience with the ClotTriever BOLD catheter for deep vein thrombosis percutaneous mechanical thrombectomy of the lower extremity

Background

The ClotTriever System is a percutaneous mechanical thrombectomy system used to treat deep vein thrombosis (DVT). The BOLD catheter is a newer compatible component with a modified coring element for which reported outcomes are limited. This retrospective study aims to assess the preliminary procedural safety and success data for patients treated with the BOLD catheter.

Methods

All consecutive patients with symptomatic lower extremity DVT who underwent thrombectomy with the BOLD catheter between 23 November 2021 and 26 June 2022 at a single center were included. Baseline and procedural characteristics were reported. The primary outcome, intraprocedural safety, was assessed by a chart review of recorded intraprocedural adverse events (AEs) or device malfunction. The secondary outcome, procedural success, was defined as ≥75% reduction in the total occlusion across treated venous segments. This was assessed by an interventionalist review of pre- and postprocedural venograms. Additional outcomes included length of postprocedural hospital stay and assessment of AEs at discharge and a 30-day follow-up visit.

Results

Eleven patient cases were reviewed. The median patient age was 65 years, the majority were women, and all were treated unilaterally. All procedures were completed in a single session without intraprocedural AEs or device malfunction. The median procedural blood loss was 50 ml. A review of pre- and postprocedural venograms showed that 35 venous segments were treated, including the femoral (n = 9), common femoral (n = 9), external iliac (n = 10), and common iliac (n = 7) veins. Procedural success was achieved in 10 patients (90.9%), and the median reduction rate in venous occlusion was 100%. The median length of postprocedural hospital stay was 1 day, and no AEs were noted at discharge (N = 11). One adverse event occurred among the eight patients who completed their follow-up visit. A patient with advanced-stage cancer and medication failure had a recurrent DVT 13 days postprocedure, which was not related to the device or procedure.

Conclusions

No safety concerns concerning the BOLD catheter were raised during the review of the cases included in this analysis, and the device was successful in reducing venous occlusion in patients with symptomatic proximal lower extremity DVT.

Acute and chronic venous occlusion

This review article provides an overview of acute and chronic venous occlusion, a condition that can cause significant morbidity and mortality if not diagnosed and treated promptly. The article begins with an introduction to the anatomy of the venous system, followed by a discussion of the causes and clinical features of venous occlusion. The diagnostic tools available for the assessment of venous occlusion, including imaging modalities such as ultrasound, CT, and MRI, are then discussed, along with their respective advantages and limitations. The article also covers the treatment options for acute and chronic venous occlusion, including anticoagulant therapy and endovascular interventions. This review aims to provide radiologists with an updated understanding of the pathophysiology, diagnosis, and management of acute and chronic venous occlusion.

Time-based reperfusion in haemodynamically unstable pulmonary embolism patients: does early reperfusion therapy improve survival?

High-risk pulmonary embolism (PE) is associated with significant morbidity and mortality. Systemic thrombolysis remains the most evidenced-based treatment for haemodynamically unstable PE, but in daily clinical practice, it remains largely underused. In addition, unlike acute myocardial infarction or stroke, a clear time window for reperfusion therapy, including fibrinolysis, for high-risk PE has not been defined either for fibrinolysis or for the more recently incorporated options of catheter-based thrombolysis or thrombectomy. The aim of the present article is to review the current evidence supporting the potential benefit of earlier administration of reperfusion in haemodynamically unstable PE patients and suggest some potential strategies to further explore this issue.

Percutaneous mechanical thrombectomy to remove post-thrombotic obstructions and manage post-thrombotic syndrome-associated venous leg ulceration

BACKGROUND

Up to one half of patients with a diagnosis of deep vein thrombosis will develop post-thrombotic syndrome (PTS). Patients with PTS can develop venous leg ulcers (VLUs) due to post-thrombotic obstructions (PTOs) that contribute to prolonged ambulatory venous hypertension. The current treatments for PTS, which include chronic thrombus, synechiae, trabeculations, and inflow lesions, do not target PTOs, and such obstructions can affect stenting success. The aim of the present study was to determine whether removal of chronic PTOs using percutaneous mechanical thrombectomy would promote VLU resolution and positive outcomes.

METHODS

In this retrospective analysis, the characteristics and outcomes for patients with VLUs secondary to chronic PTO who were treated using the ClotTriever System (Inari Medical) between August 2021 and May 2022 were assessed. Technical success was considered the ability to cross a lesion and introduce the thrombectomy device. Clinical success was defined as a decrease of ≥1 in the severity category for the ulcer diameter using the revised venous clinical severity score (score 0, no VLU; score 1, mild VLU [size <2 cm]; score 2, moderate VLU [size 2-6 cm]; score 3, severe VLU [size >6 cm]) at the latest follow-up visit.

RESULTS

A total of 11 patients with 15 VLUs on 14 limbs were identified. Their mean age was 59.7 ± 11.8 years, and four patients (36.4%) were women. The median VLU duration was 11.0 months (interquartile range [IQR], 6.0-17.0 months), and 2 patients had VLUs secondary to a deep vein thrombosis event >40 years previously. All treatments were performed in a single session, with technical success achieved in 100% of the 14 limbs. A median of five passes (IQR, four to six passes) with the ClotTriever catheter were performed per limb. Chronic PTOs were successfully extirpated, and intraprocedural intravascular ultrasound showed effective disruption of venous synechiae and trabeculations. Stents were placed in 10 limbs (71.4%). The time to VLU resolution or the latest follow-up was 12.8 ± 10.5 weeks, and clinical success was achieved for all 15 VLUs (100%), with the revised venous clinical severity score for the ulcer diameter improving from a median of 2 (IQR, 2-2) at baseline to a median score of 0 (IQR, 0-0) at last follow-up. The VLU area had decreased by 96.6% ± 8.7%. Of the 15 VLUs, 12 (80.0%) had resolved completely, and 3 had demonstrated near-complete healing.

CONCLUSIONS

All patients showed complete or near-complete VLU healing within a few months after mechanical thrombectomy. Mechanical extirpation and interruption of chronic PTOs allowed for luminal gain and restoration of cephalad inflow. With additional investigation, mechanical thrombectomy with the study device could prove a vital component to the treatment of VLUs secondary to PTOs.

An unexpected recurrence of rectal squamous cell cancer presenting as deep vein thrombosis

Tumor thrombus is an uncommon oncologic complication and is exceedingly rare in the setting of colorectal cancer. We present the case of a 71-year-old woman with a significant oncologic history, including rectal squamous cell cancer, who presented with left lower extremity deep vein thrombosis. She underwent left lower extremity venography and thrombectomy of the left common iliac vein. Pathologic examination revealed fragments of squamous cell carcinoma embedded in an organizing thrombus. A covered stent was placed in the common iliac vein across the internal iliac vein origin. Positron emission tomography-computed tomography confirmed mediastinal and retroperitoneal lymphadenopathy, which was managed with adjuvant carboplatin and paclitaxel chemotherapy.

Location, location, location: Fibrin, cells, and fibrinolytic factors in thrombi

Thrombi are heterogenous in nature with composition and structure being dictated by the site of formation, initiating stimuli, shear stress, and cellular influences. Arterial thrombi are historically associated with high platelet content and more tightly packed fibrin, reflecting the shear stress in these vessels. In contrast, venous thrombi are generally erythrocyte and fibrin-rich with reduced platelet contribution. However, these conventional views on the composition of thrombi in divergent vascular beds have shifted in recent years, largely due to recent advances in thromboectomy and high-resolution imaging. Interestingly, the distribution of fibrinolytic proteins within thrombi is directly influenced by the cellular composition and vascular bed. This in turn influences the susceptibility of thrombi to proteolytic degradation. Our current knowledge of thrombus composition and its impact on resistance to thrombolytic therapy and success of thrombectomy is advancing, but nonetheless in its infancy. We require a deeper understanding of thrombus architecture and the downstream influence on fibrinolytic susceptibility. Ultimately, this will aid in a stratified and targeted approach to tailored antithrombotic strategies in patients with various thromboembolic diseases.

Outcomes from the ClotTriever Outcomes Registry show symptom duration may underestimate deep vein thrombus chronicity

OBJECTIVE

The all-comer ClotTriever Outcomes registry assessed indicators of thrombus chronicity in patients with acute, subacute, and chronic lower extremity deep vein thrombosis (DVT). The effectiveness of the ClotTriever System (Inari Medical, Irvine, CA) by chronicity subgroup was also assessed and reported here in this subanalysis.

METHODS

All-comer patients with lower extremity DVT were enrolled, with no limitation based on the patients' symptom duration. Chronicity was assessed three times and compared: before the procedure based on symptom duration, during the procedure based on available pre-thrombectomy imaging, and visual inspection of the extracted thrombus morphology after thrombectomy. Patients were grouped into acute, subacute, and chronic subgroups according to their post-thrombectomy thrombus chronicity based on thrombus morphology. Analyses on baseline and procedural characteristics along with thrombus removal were performed across subgroups. The effectiveness of thrombus removal was determined by Marder scores adjudicated by an independent core laboratory, with a prespecified primary effectiveness end point of complete or near-complete (≥75%) thrombus removal.

RESULTS

Of the 260 treated limbs from 250 patients, using symptom duration alone, 70.7% were considered acute, 20.9% subacute, and 8.4% chronic. Upon visual inspection, the extracted thrombus chronicity was approximately one-third in each subgroup: 32.7% had acute thrombus, 35.4% subacute thrombus, and 31.9% chronic thrombus. Chronicity assessed using symptom duration alone mismatched the post-thrombectomy chronicity in 55.1% of limbs (P < .0001) with 49.0% being more chronic than suggested by the patients' duration of symptoms. Chronicity assessed using pre-thrombectomy imaging mismatched the post-thrombectomy chronicity in 17.5% of limbs (P < .0001). No patients received thrombolytics and 99.6% were treated in a single session. Complete or near-complete thrombus removal was achieved in a high percentage of limbs regardless of thrombus chronicity: 90.8%, 81.9%, and 83.8% in limbs with acute, subacute, and chronic thrombus, respectively.

CONCLUSIONS

This subanalysis from the all-comer ClotTriever Outcomes registry demonstrates that extracted thrombus in DVT may be more chronic than suggested by the patients' duration of symptoms. The addition of imaging is helpful to determine the ability of thrombus to respond to therapy. Irrespective of thrombus chronicity, the ClotTriever system can be effective at removing acute, subacute, and chronic thrombus in a single-session procedure without the need for thrombolytics.

Thrombus Structural Composition in Cardiovascular Disease

Thrombosis is a major complication of cardiovascular disease, leading to myocardial infarction, acute ischemic stroke, or venous thromboembolism. Thrombosis occurs when a thrombus forms inside blood vessels disrupting blood flow. Developments in thrombectomy to remove thrombi from vessels have provided new opportunities to study thrombus composition which may help to understand mechanisms of disease and underpin improvements in treatments. We aimed to review thrombus compositions, roles of components in thrombus formation and stability, and methods to investigate thrombi. Also, we summarize studies on thrombus structure obtained from cardiovascular patients and animal models. Thrombi are composed of fibrin, red blood cells, platelets, leukocytes, and neutrophil extracellular traps. These components have been analyzed by several techniques, including scanning electron microscopy, laser scanning confocal microscopy, histochemistry, and immunohistochemistry; however, each technique has advantages and limitations. Thrombi are heterogenous in composition, but overall, thrombi obtained from myocardial infarction are composed of mainly fibrin and other components, including platelets, red blood cells, leukocytes, and cholesterol crystals. Thrombi from patients with acute ischemic stroke are characterized by red blood cell- and platelet-rich regions. Thrombi from patients with venous thromboembolism contain mainly red blood cells and fibrin with some platelets and leukocytes. Thrombus composition from patients with myocardial infarction is influenced by ischemic time. Animal thrombosis models are crucial to gain further mechanistic information about thrombosis and thrombus structure, with thrombi being similar in composition compared with those from patients. Further studies on thrombus composition and function are key to improve treatment and clinical outcome of thrombosis.