Ovine Iliac Vein Model for Endovascular Thrombectomy of Acute Deep Venous Thrombosis

Immune-mediated regeneration of cell-free vascular grafts in an ovine model

We developed acellular tissue engineered vessels (ATEV) using small intestine submucosa (SIS) incorporating heparin and a novel protein named H2R5. ATEVs were implanted into the arterial circulation of an ovine animal model, demonstrating high primary patency rates over a period of three months. Implanted grafts were infiltrated by host cells, the majority of which were monocytes/macrophages (MC/MΦ), as demonstrated by scRNA sequencing and immunostaining. They also developed functional endothelial and medial layers that deposited new extracellular matrix leading to matrix remodeling and acquisition of mechanical properties that were similar to those of native arteries. Notably, during this short implantation time, ATEVs turned into functional neo-arteries, as evidenced by the development of the vascular contractile function. Our findings underscore the potential of H2R5-functionalized ATEVs as promising candidates for tissue replacement grafts in a large pre-clinical animal model and highlight the contribution of macrophages in vascular regeneration.

Assessment of Catheter-Directed Thrombolysis and Histotripsy Treatment for Deep Vein Thrombosis

PURPOSE

The hypothesis of this study was that histotripsy, an ultrasound therapy that disrupts tissue mechanically through the action of bubble clouds, increases the short-term rate of acute thrombus clearance for catheter-directed thrombolysis (CDT) in an animal model.

MATERIALS AND METHODS

Thrombi formed in the femoral vein of pigs were treated with CDT, histotripsy, or CDT and histotripsy (histotripsy+). Ultrasound (B-mode and color Doppler) and contrast fluoroscopy imaging data were scored by 4 observers for semiquantitative evaluation of each arm with ordinal regression models. Further, B-mode images were manually annotated by 3 observers to quantify the thrombus clearance rate.

RESULTS

A total of 27 thrombi (2.0 cm [SD ± 0.4] in length) in 27 animals were considered in this study (N = 8 for CDT, N = 9 for histotripsy, and N = 10 for histotripsy+). The mean treatment duration was 20.2 minutes (SD ± 1.3). The ordinal regression models indicated that the thrombus clearance rate increased for histotripsy+ relative to CDT based on B-mode and color Doppler but not fluoroscopy (P = .015, P = .001, and P = .900, respectively). Manual annotation of B-mode images denoted that histotripsy+ had an increased thrombus clearance rate relative to CDT and histotripsy (P = .001 and P = .022, respectively). Petechial hemorrhage was present in the perivascular soft tissue for 2 cases with histotripsy and 1 case with histotripsy+.

CONCLUSIONS

The clearance of acute thrombus was similar for treatment with CDT or histotripsy. Combining these individual approaches further increased the rate of thrombus clearance based on multiple imaging metrics.

Preclinical evaluation of a novel endovascular thrombectomy device in a modified swine model for iliac vein thrombosis

Objective

To evaluate the safety and efficacy of a novel endovascular thrombectomy device in a modified swine model of iliac vein thrombosis.

Methods

A modified swine model for iliac vein thrombosis was created using proximal‒distal balloon occlusion combined with autologous venous thrombus and thrombin injections. The safety and efficacy of the newly developed Zylox endovascular thrombectomy system were evaluated in this animal model and its performance was compared with that of the AcoStream aspiration thrombectomy device.

Results

Bilateral iliac vein thrombosis models were successfully created in 12 swine, with 23 iliac veins used for device testing and one for anatomical observation. The thrombus length in the Zylox group was greater than in the AcoStream group (98.42 ± 17.56 mm vs. 84.12 ± 13.30 mm), while thrombus scores were not significantly different between the two groups. Although Grade I thrombus clearance was achieved in all iliac veins in both groups, blood loss in the Zylox group was significantly less than in the AcoStream group (81.09 ± 27.26 ml vs. 162.50 ± 61.96 ml, P < 0.001). Three swine (6 iliac veins) in each group underwent repeat venography evaluations 28 days postthrombectomy, showing that all the veins were patent without any rethrombosis. Histopathologic evaluation immediately and 28 days postthrombectomy revealed no differences between the two groups. No complications or deaths occurred in the swine during the entire process.

Conclusion

The current modified swine model is stable, reproducible, and appropriate for testing endovascular devices. This study preliminarily verified the safety and efficacy of the Zylox thrombectomy system for thrombus removal in this animal model and demonstrated its advantage in controlling blood loss. Future randomized controlled trials in humans are needed to further verify the safety and efficacy of the device.

Histological Features of In-Stent Restenosis after Iliac Vein Thrombus Removal and Stent Placement in a Goat Model

PURPOSE

To establish an animal model for in-stent restenosis (ISR) after postthrombotic iliac vein stent placement and characterize histopathological changes in tissue within the stented vein.

MATERIALS AND METHODS

Iliac vein thrombosis was induced using balloon occlusion and thrombin injection in 8 male Boer goats. Mechanical thrombectomy and iliac vein stent placement were performed 3 days after thrombosis induction. Restenosis was evaluated by venography and optical coherence tomography (OCT) at 1 and 8 weeks after stent placement, and stent specimens were taken for pathological examination after the animals were euthanized.

RESULTS

Thrombosis induction was successful in all 8 goats, with >80% iliac vein occlusion. After thrombus removal, OCT revealed considerable venous intimal thickening and a small number of mural thrombi. Neointimal hyperplasia with thrombus formation was observed in all goats 1 week after stent implantation; the degree of ISR was 15%-33%. At 8 weeks, the degree of ISR was 21%-32% in 3 goats, and stent occlusion was observed in 1 goat. At 1 week, the neointima predominantly consisted of fresh thrombi. At 8 weeks, proliferplastic fibrotic tissue and smooth muscle cells (SMCs) were predominant, and the stent surfaces were endothelialized in 2 of 3 goats and partially endothelialized in 1 goat.

CONCLUSIONS

In the goat model, postthrombotic neointimal hyperplasia in the venous stent may result from time-dependent thrombus formation and organization, accompanied by migration and proliferation of SMCs, causing ISR. These results provide a basis to further explore the mechanism of venous ISR and promote the development of venous stents that reduce neointimal hyperplasia.

Comparison of Fibered versus Nonfibered Coils for Venous Embolization in an Ovine Model

PURPOSE

To compare nylon fibered (F) with nonfibered (NF) coils for embolization in an ovine venous model.

MATERIALS AND METHODS

Four- to 8-mm-diameter, 0.035-inch F and NF coils were deployed in 24 veins in 6 sheep. The number of coils, total length of the coils, and length of implanted coil pack required to achieve complete stasis were recorded, as were vessel diameter, radiation dose, ease of packing, damage to embolized vessel, and time to stasis. Venography at 1 and 3 months was used to assess the migration and durability of vessel occlusion. Veins were harvested at 3 months.

RESULTS

F and NF coils were deployed in 24 veins, and stasis was achieved, without immediate coil migration or vessel damage. The mean numbers of F and NF coils per vein were 5 and 8.75, respectively (P = .007). The vessel diameter between the groups was not statistically different. The total coil length (F, 70 cm vs NF, 122.5 cm; P = .0007), coil pack length (F, 29.3 mm vs NF, 39.4 mm; P = .003), time to stasis (F, 5.3 minutes vs NF, 9.0 minutes; P = .008), and radiation dose (F, 25.3 mGy vs NF, 34.9 mGy; P = .037) were significantly different between the groups. Challenges with the animal model prevented conclusive long-term results. Migration occurred with 8 of 11 (72%) coil packs in the femoral veins and 0 of 13 (0%) coil packs in the internal iliac and deep femoral veins. Venography demonstrated that of 16 remaining coil packs, 11 were occluded at 1 month and 10 remained occluded at 3 months.

CONCLUSIONS

Fibers allow for significantly fewer coils to achieve immediate venous occlusion.