Endovascular Porcine Model of Iliocaval Venous Thrombosis

Experimental multiparametric magnetic resonance imaging characterization of iliocaval venous thrombosis pathological changes

OBJECTIVE

Iliocaval thrombotic obstruction is a challenging condition, especially because thrombus age and corresponding pathological remodeling at presentation are unknown, which directly impacts management. Our aim was to assess the ability of magnetic resonance imaging (MRI) in determining age thresholds of experimentally created inferior vena cava (IVC) thrombosis in pigs.

METHODS

We used a previously described swine model of IVC thrombosis. The animals underwent MRI at baseline, immediately after thrombosis creation, and after a follow-up period extending from 2 to 28 days. Thirteen pigs were divided into three groups according to disease chronicity: acute group (AG; n = 5), subacute group (SAG; n = 4), and chronic group (CG; n = 4), with a mean thrombosis age of 6.4 ± 2.5 days, 15.7 ± 2.8 days, and 28 ± 5.7 days, respectively. A T1-weighted volumetric interpolated breath-hold examination sequence was used to anatomically delineate IVC thrombus as a region of interest. Three other MRI sequences were used to assess the thrombus signal.

RESULTS

The Kruskal-Wallis test showed a statistically significant difference in T1 relaxation times after contrast injection (P = .026) between the three groups of chronicity. The AG (360.2 ± 102.5 ms) was significantly different from the CG (336.7 ± 55.2 ms; P = .003), and the SAG (354.1 ± 89.7 ms) was significantly different from the AG (P = .027). There was a statistically significant difference in native T2 relaxation times (P = .038) between the three groups. The AG (160 ± 86.7 ms) was significantly different from the SAG (142.3 ± 55.4 ms; P = .027), and the SAG was significantly different from the CG (178.4 ± 11.7 ms; P = .004).

CONCLUSIONS

This study highlighted MRI characteristics in a swine model that might have the potential to significantly differentiate subacute and chronic stages from an acute stage of deep vein thrombosis in humans. Further clinical studies in humans are warranted.

CLINICAL RELEVANCE

In addition to providing a better understanding of venous thrombosis remodeling over time, magnetic resonance imaging has the potential to be a tool that could allow us to characterize the composition of venous thrombus over an interval, allowing for a refined analysis of the local evolution of venous thrombosis. We propose a noninvasive and innovative method to characterize different thresholds of chronicity with magnetic resonance imaging features of central deep vein thrombosis of the inferior vena cava experimentally obtained using a totally endovascular in vivo swine model, mimicking human pathophysiology. Being able to determine these features noninvasively is critical for vascular specialists when it comes to choosing between fibrinolytic therapy, percutaneous thrombectomy, or surgical management.

Prevalence and risk factors for proximal deep vein thrombosis at admission in patients with traumatic fractures: a multicenter retrospective study

Objective

This study aimed to determine the associated risk factors for proximal deep vein thrombosis (DVT) in patients with lower extremity and pelvic-acetabular fractures.

Methods

The medical records of 4,056 patients with lower extremity and pelvic-acetabular fractures were retrospectively reviewed. The patients were classified into proximal or non-proximal DVT groups. Logistic regression models were used to determine the independent risk variables for proximal DVT. The predictive value of the related risk factors was further analyzed using receiver operating characteristic curves.

Results

The prevalence of proximal DVT was 3.16%. Sex, body mass index (BMI), fracture site, injury mechanism, diabetes, coronary heart disease (CHD), injury-to-admission interval, hematocrit, platelet counts, and D-dimer levels differed significantly between the two groups. BMI ≥ 24.0 kg/m2, femoral shaft fractures, high-energy injury, diabetes, injury-to-admission interval >24 h were independent risk factors for proximal DVT. CHD decreased the risk of proximal DVT. The platelet and D-dimer had high negative predictive value for predicting proximal DVT formation, with cut-off values of 174 × 109/L and 2.18 mg/L, respectively.

Conclusion

BMI ≥ 24.0 kg/m2, femoral shaft fractures, high-energy injury, diabetes, injury-to-admission interval >24 h were independent risk factors for proximal DVT in patients with lower extremity and pelvic-acetabular fractures. Platelet count and D-dimer level were effective indicators for excluding proximal DVT occurrence. CHD decreased the risk of proximal DVT.

Venous thromboembolism swine model with reflux-induced venous hypertension

Objective

This study describes a novel swine model of venous thromboembolism (VTE) with reflux-induced venous hypertension.

Methods

Six pigs underwent disruption of the tricuspid chordae tendineae to create reflux and venous hypertension in the femoral vein. The vein was traumatized 2 to 3 weeks later by repeated withdrawal of a slightly overinflated occlusion balloon across the lumen, followed by balloon occlusion of the outflow. A small amount of thrombin was injected into the traumatized vein segment immediately after outflow occlusion. Thrombosis of the traumatized vein evolved into an organized thrombus seven weeks later. The histological features of the harvested post-thrombotic femoral vein were studied with hematoxylin and eosin and Trichrome stains.

Results

In all six pigs, initial disruption of the chordae tendineae was successfully performed to create tricuspid reflux and venous hypertension. After two-stage sequential procedures, a thrombus formed in the target femoral vein segment. Histology of the harvested thrombotic vein showed features of an organizing thrombus with collagen formation and fibrosis.

Conclusions

The novel swine VTE model may serve as a platform for developing and testing human-sized therapeutic procedures and devices in translational venous research.

Clinical Relevance

This study describes a swine model of VTE created by incorporating all three elements of Virchow's triad. The model uniquely incorporates reflux-induced venous hypertension, which may be used in studying venous insufficiency and VTE in those with systemic venous hypertension. Likewise, this model may serve as a platform for development and evaluation of diagnostic imaging or therapeutic procedures and devices in subjects with systemic venous hypertension.

Comparison between canine and porcine models of chronic deep venous thrombosis

OBJECTIVE

To first induce chronic deep venous thrombosis in the left iliac veins of canines and porcines and then compare these two models to validate endovascular treatment devices.

METHODS

Thrombin and fibrinogen were used to produce a solid thrombus in the left iliac veins of a stenosis model. The researchers used venous angiography and histological staining to investigate the progression of thrombosis.

RESULTS

A left iliac vein thrombus was successfully formed in all experimental animals, including six Labrador dogs and three Bama miniature pigs, and there was minimal surgical bleeding. All dogs survived until 90 days, and three pigs died on Days 29, 33, and 58.

CONCLUSION

The researchers first established the models and then observed the progression of chronic deep venous thrombosis of the iliac vein in large animals for up to 90 days. Dogs are better suited for chronic deep venous thrombosis models due to their uncomplicated anatomy, excellent obedience, and proneness to physical activity compared with pigs.

Double-Barrel Nitinol Stent Placement for Iliocaval Reconstruction: The Effect of Deployment Sequence and Direction on Final Configuration

Double-barrel stent placement across the iliocaval confluence is commonly used for the treatment of chronic bilateral iliocaval occlusion. The difference in the deployment outcomes of synchronous parallel stent deployment versus asynchronous or antiparallel deployment and the underlying stent interactions are poorly understood. In this study, 3 strategies of double-barrel nitinol self-expanding stent deployment across the iliocaval confluence (synchronous parallel, asynchronous parallel, and synchronous antiparallel) were contrasted in vivo in 3 swine followed by assessment of the explanted stent construct. Synchronous parallel stent deployment achieved a desired double-barrel configuration. The asynchronous parallel and antiparallel deployment strategies both resulted in a crushed stent despite subsequent simultaneous balloon angioplasty. These animal model results suggested that in patients who undergo double-barrel iliocaval reconstruction, synchronous parallel stent deployment may provide the desired stent conformation and increase the chance for clinical success.

Venous congestion affects neuromuscular changes in pigs in terms of muscle electrical activity and muscle stiffness

Early detection of venous congestion (VC)-related diseases such as deep vein thrombosis (DVT) is important to prevent irreversible or serious pathological conditions. However, the current way of diagnosing DVT is only possible after recognizing advanced DVT symptoms such as swelling, pain, and tightness in affected extremities, which may be due to the lack of information on neuromechanical changes following VC. Thus, the goal of this study was to investigate acute neuromechanical changes in muscle electrical activity and muscle stiffness when VC was induced. The eight pigs were selected and the change of muscle stiffness from the acceleration and muscle activity in terms of integral electromyography (IEMG) was investigated in three VC stages. Consequently, we discovered a significant increase in the change in muscle stiffness and IEMG from the baseline to the VC stages (p < 0.05). Our results and approach can enable early detection of pathological conditions associated with VC, which can be a basis for further developing early diagnostic tools for detecting VC-related diseases.

Thrombosis Models: An Overview of Common In Vivo and In Vitro Models of Thrombosis

Occlusions in the blood vessels caused by blood clots, referred to as thrombosis, and the subsequent outcomes are leading causes of morbidity and mortality worldwide. In vitro and in vivo models of thrombosis have advanced our understanding of the complex pathways involved in its development and allowed the evaluation of different therapeutic approaches for its management. This review summarizes different commonly used approaches to induce thrombosis in vivo and in vitro, without detailing the protocols for each technique or the mechanism of thrombus development. For ease of flow, a schematic illustration of the models mentioned in the review is shown below. Considering the number of available approaches, we emphasize the importance of standardizing thrombosis models in research per study aim and application, as different pathophysiological mechanisms are involved in each model, and they exert varying responses to the same carried tests. For the time being, the selection of the appropriate model depends on several factors, including the available settings and research facilities, the aim of the research and its application, and the researchers' experience and ability to perform surgical interventions if needed.