Prototype percutaneous thrombolytic device: preclinical testing in subacute inferior vena caval thrombosis in a pig model

Endovascular Porcine Model of Iliocaval Venous Thrombosis

OBJECTIVE

To develop a large animal model of iliocaval deep venous thrombosis (DVT), which enables development and evaluation of interventional management and existing imaging modalities.

METHODS

The experimental protocol consisted of a total endovascular approach. Pigs were percutaneously accessed through the right internal jugular and bilateral femoral veins. Three balloon catheters were inflated to induce venous stasis in the infrarenal inferior vena cava (IVC) and bilateral common iliac veins (CIVs). Hypercoagulability was induced by injecting 10 000 IU of thrombin. After 2.5 hours, the balloon catheters were removed before animal recovery. After seven, 14, 21, 28, or 35 days, animals were euthanised; the IVC and CIV were harvested en bloc, cross sectioned and prepared for histological examination. Multimodal imaging was performed before and after thrombus creation, and before animal euthanasia.

RESULTS

Thirteen female domestic pigs with a mean weight of 59.3 kilograms were used. The mean maximum IVC diameter and area were 16.4 mm and 1.2 cm², respectively. The procedure was successful in 12 animals with occlusive venous thrombosis in the region of interest on immediate post-operative magnetic resonance venography and a mean thrombus volume of 19.8 cm³. Clinical pathology results showed platelet consumption, D dimer increase, and inflammatory response. Histological evaluation demonstrated a red cell, fibrin, and platelet rich thrombus on day 1, with progressive inflammatory cell infiltration from day 7. Collagen deposition appeared in week 2 and neovascularisation in week 3.

CONCLUSION

Endovascular occlusion combined with thrombin infusion is a reliable minimally invasive approach to produce acute and subacute DVT in a large animal model.

A Preclinical Porcine Model of Portal Vein Thrombosis in Liver Cirrhosis

Background

This study aimed at presenting a novel method of developing a porcine model of portal vein thrombosis (PVT) in cirrhosis by intravenous administration of thrombin and insertion of a fibered coil. We further investigated changes of biochemical parameters, coagulation, and proinflammatory cytokine expression in the cirrhosis-PVT group.

Methods

Twelve male pigs were randomized into the control group (n = 3) and cirrhosis group (n = 9). In cirrhotic pigs, three were randomly selected to establish PVT by ultrasound-guided percutaneous puncture of the main portal vein (MPV) followed by intravenous thrombin administration and fibered coil insertion. Thrombosis in the MPV was detected by abdominal enhanced computer tomography (CT). The changes of hepatic function, coagulation system, and inflammation cytokines were compared among normal, cirrhosis, and cirrhosis with PVT groups.

Results

As manifested by the presence of a filling defect in MPV on portal venous-phase CT angiography, fibrin thrombi were formed in the MPV in cirrhotic pigs within one week and persisted for four weeks. Five weeks after surgery, abnormal liver functions occurred in association with PVT formation in cirrhosis. Both coagulation and thromboelastography parameters showed that cirrhosis-PVT pigs exhibited a procoagulant state through hyperfunction of platelets and clotting factors. Interleukin 6 (IL-6) as a potential inflammatory marker stimulated PVT-mediated inflammation activation in cirrhosis.

Conclusions

Our study provides in vivo evidence that intravenous injection of a coil and thrombin into MPV under interventional guided devices enables a feasible method in thrombus creation. Further exploration and validation of large-sample cases are required to characterize utilities of this model.

Critical Review of Large Animal Models for Central Deep Venous Thrombosis

OBJECTIVE

To review the existing literature on large animal models of central venous thrombosis (CVT) and to evaluate its relevance in regard to the development and testing of dedicated therapeutics applicable to humans.

METHODS

A systematic literature search was conducted in PubMed and Embase. Articles describing an in vivo experimental protocol of CVT in large animals, involving the iliac vein and/or the vena cava and/or the brachiocephalic vein, were included. The primary aim of the study, animal characteristics, experimental protocol, and thrombus evaluation were recorded.

RESULTS

Thirty-eight papers describing more than 30 different protocols were included. Animals used were pigs (53%), dogs (21%), monkeys (24%), and cattle (3%). The median number of animals per study was 12. Animal sex, strain, and weight were missing in 18 studies (47%), seven studies (18%), and eight studies (21%), respectively. CVT was always induced by venous stasis: solely (55%), or in addition to hypercoagulability (37%) or endothelial damage (10%). The size of the vessel used for thrombus creation was measured in four studies (10%). Unexpected animal death occurred in nine studies (24%), ranging from 3% to 37% of the animals. Twenty-two studies (58%) in the acute phase and 31 studies in the chronic phase (82%) evaluated the presence or absence of the thrombus created, and its occlusive characteristic was reported, respectively, in five and 17 studies. Histological examination was performed in 24 studies (63%) with comparison to human thrombus in one study.

CONCLUSION

This review showed advantages and weaknesses of the existing large animal models of CVT. Future models should insist on more rigour and consistency in reporting animal characteristics, as well as evaluating and comparing the thrombus created to human thrombus.

Molecular magnetic resonance imaging of deep vein thrombosis using a fibrin-targeted contrast agent: a feasibility study

PURPOSE

To evaluate the value of a fibrin-specific MR contrast agent (EP-2104R; EPIX Pharmaceuticals) for detection of deep vein thrombosis (DVT) and monitoring of percutaneous intervention for treatment.

MATERIALS AND METHODS

In 6 domestic swine, DVT was induced in an iliac/femoral vein using an occlusion-balloon catheter and subsequent injection of thrombin. The occluded vessels were recanalized by mechanical thrombectomy using a Fogarty catheter and an Arrow rotating thrombectomy device. Magnetic resonance imaging of the pelvis and lung was repeated 4 times (before and after DVT induction, after contrast agent administration, and after intervention) using a 1.5-T whole-body XMR system (ACS-NT, Philips Medical Systems, Best, NL). The visualization of the thrombi and contrast-to-noise ratio (CNR) was assessed.

RESULTS

EP-2104R allowed selective visualization of thrombi with accurate determination of the extent of DVT with high contrast (CNR: 65.3 +/- 17.2). After intervention, dislodged thrombus fragments were selectively visualized in the lung (CNR: 27.9 +/- 9.3).

CONCLUSIONS

Molecular magnetic resonance imaging using fibrin-specific MR contrast agent EP-2104R allowed for selective visualization of DVT and monitoring of percutaneous intervention.

A porcine deep vein thrombosis model for magnetic resonance-guided monitoring of different thrombectomy procedures

PURPOSE

To establish a porcine model of deep iliac vein thrombosis, which allows monitoring of thrombectomy and thrombolytic procedures by magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Deep iliac vein thrombosis was induced in 12 domestic swine using an occlusion-balloon catheter and subsequent injection of thrombin distal to the occluded vessel site. Thrombosis induction was successfully achieved in all animals after 1 hour as verified by MRI. In addition, x-ray fluoroscopy was performed for comparison. Subsequently, thrombectomy was performed using a Fogarty catheter, an Arrow-Trerotola percutaneous thrombolytic device as well as electrical discharge-induced shock waves. The latter procedure was carried out with and without additional administration of Actilyse. MRI and x-ray fluoroscopy were repeated to monitor therapy.

RESULTS

After successful thrombosis induction within the deep iliac veins in all cases, thrombus material could be completely removed using the Fogarty catheter and the Arrow-Trerotola percutaneous thrombolytic device, whereas electrical discharge-induced shock wave failed to recanalize the occluded vessel even if additional Actilyse was administered. The actual burden of thrombotic material could be reliably visualized using MRI.

CONCLUSIONS

A porcine model of deep iliac vein thrombosis model is presented, which permits reliable visualization of thrombotic material. This model might be a useful tool to compare different thrombectomy devices or to evaluate the effectiveness of new thrombolytic approaches.

Mechanical Thrombectomy of Acute Iliofemoral Deep Vein Thrombosis with Use of an Arrow-Trerotola Percutaneous Thrombectomy Device

PURPOSE

To evaluate the immediate and 1-year clinical outcomes of mechanical thrombectomy with use of the Arrow-Trerotola percutaneous thrombectomy device (PTD) with or without low-dose urokinase in the treatment of acute iliofemoral deep vein thrombosis (DVT).

MATERIALS AND METHODS

Mechanical thrombectomy with the PTD was performed in 25 patients with acute iliofemoral DVT. Thrombolytic therapy with low-dose urokinase was used in all patients without contraindications (n = 20). Other therapies used in combination included inferior vena cava filter insertion (n = 5), sheath aspiration thrombectomy (n = 25), and angioplasty and stent placement (n = 20).

RESULTS

Initial technical and clinical success was achieved in all cases. In the 20 patients who had no contraindications to the use of urokinase, the dosage of urokinase did not exceed 1 million IU (range, 360,000-1,000,000 IU; mean, 640,000 IU). The mean time of urokinase infusion was 16 hours (range, 12-20). In five patients who had a contraindication to the use of urokinase, mechanical thrombectomy with the PTD was successful without the use of urokinase. There were no major complications. Primary patency of the stent-implanted common iliac vein segment was achieved at 1 year in 17 of 20 patients (85%). The overall 1-year clinical success rate was 92% (23 of 25 patients). Valvular insufficiency occurred in two patients (8%).

CONCLUSION

The PTD is an effective mechanical thrombectomy device in the treatment of acute iliofemoral DVT with or without adjunctive urokinase thrombolysis.

Percutaneous Venous Thrombectomy Using the Arrow-Trerotola Percutaneous Thrombolytic Device (PTD) with Temporary Caval Filtration: In Vitro Investigations

PURPOSE

To evaluate the size and quantity of downstream emboli after thrombectomy using the Arrow-Trerotola Percutaneous Thrombolytic Device (PTD) with or without temporary filtration for extensive iliofemoral and iliocaval thrombi in an in vitro flow model.

METHODS

Iliocaval thrombi were simulated by clotted bovine blood in a flow model (semilucent silicone tubings, diameter 12-16 mm). Five experimental set-ups were performed 10 times each; thrombus particles and distribution were measured in the effluent. First, after retrograde insertion, mechanical thrombectomy was performed using the PTD alone. Then a modified self-expanding tulip-shaped temporary vena cava stent filter was inserted additionally at the beginning of each declotting procedure and removed immediately after the intervention without any manipulation within or at the filter itself. In a third step, the filter was filled with thrombus only. Here, two experiments were performed: Careful closure within the flow circuit without any additional fragmentation procedure and running the PTD within the filter lumen, respectively. In the final set-up, mechanical thrombectomy was performed within the thrombus-filled tubing as well as in the filter lumen. The latter was closed at the end of the procedure and both devices were removed from the flow circuit.

RESULTS

Running the PTD in the flow circuit without filter protection led to a fragmentation of 67.9% (+/-7.14%) of the clot into particles < or =500 microm; restoration of flow was established in all cases. Additional placement of the filter safely allowed maceration of 82.9% (+/-5.59%) of the thrombus. Controlled closure of the thrombus-filled filter within the flow circuit without additional mechanical treatment broke up 75.2% (+/-10.49%), while additional mechanical thrombectomy by running the PTD within the occluded filter led to dissolution of 90.4% (+/-3.99%) of the initial clot. In the final set-up, an overall fragmentation rate of 99.6% (+/-0.44%) was achieved.

CONCLUSIONS

The combined use of the Arrow-Trerotola PTD and a temporary vena cava stent filter proved to be effective for even large clot removal in this experimental set-up.

Endovascular management of venous thrombotic and occlusive diseases of the lower extremities

Acute complications of deep vein thrombosis (DVT) of the lower extremities include pulmonary embolism and venous ischemia. Delayed complications include a spectrum of debilitating symptoms referred to as postthrombotic syndrome (PST). Anticoagulation therapy is recognized as the mainstay of therapy in acute DVT. However, there are few data to suggest any major beneficial effect on PTS, which is thought to be mediated by valve damage and/or occlusive chronic thrombus and venous scarring. Endovascular catheter-directed thrombolysis techniques with pharmacologic thrombolytic agents, used alone or in combination with mechanical thrombectomy devices, have been proven highly effective in clearing acute DVT, which may allow the preservation of venous valve function and prevention of subsequent venous occlusive disease. Definitive management of underlying anatomic occlusive abnormalities can also be undertaken.

Validation of US-guided percutaneous venous access and manual compression for studies in swine

PURPOSE

To validate, in swine, the feasibility, efficacy, and safety of ultrasound (US)-guided vascular access, with manual compression for hemostasis, as an alternative to surgical cutdown.

MATERIALS AND METHODS

US-guided femoral vein access was attempted 22 times in eight pigs. Bilateral access was performed in the initial procedure (eight pigs, 16 veins), and unilateral access was performed during follow-up procedures (six pigs, six veins). Two sheath sizes were used: 9 F (in eight veins) and 8 F (in 14 veins). At the completion of each procedure, the vascular sheaths were removed and hemostasis was attempted by manual compression. All animals were followed clinically for at least 24 hours after each access procedure. Bilateral US images of the femoral region were obtained in six pigs (12 puncture sites) 2 weeks after the initial procedure.

RESULTS

US-guided femoral vein access was successful in all 22 attempts, including 16 first-time insertions and six subsequent insertions. Hemostasis was achieved with 5 minutes of manual compression in all 22 procedures. No groin complications were identified on clinical follow-up or at necropsy. US imaging of the 12 femoral access points in the six pigs that underwent more than one procedure demonstrated normal femoral veins that compressed appropriately with no evidence of thrombosis or hematoma.

CONCLUSION

US-guided femoral vein access, with manual compression used for hemostasis, is a safe and effective method for venous interventions in swine. Moreover, this percutaneous technique allows the same vessel to be reused.