Evaluation of thrombolysis in a porcine model of chronic deep venous thrombosis: an endovascular model

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.

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.

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.

Pulmonary artery embolism: comprehensive transcriptomic analysis in understanding the pathogenic mechanisms of the disease

BACKGROUND

Pulmonary embolism (PE) is a severe disease that usually originates from deep vein thrombosis (DVT) of the lower extremities. This study set out to investigate the changes in the transcriptome of the pulmonary artery (PA) in the course of the PE in the porcine model.

METHODS

The study was performed on 11 male pigs: a thrombus was formed in each right femoral vein in six animals, and then was released to induce PE, the remaining five animals served as a control group. In the experimental animals total RNA was isolated from the PA where the blood clot lodged, and in the control group, from the corresponding PA segments. High-throughput RNA sequencing was used to analyse the global changes in the transcriptome of PA with induced PE (PA-E).

RESULTS

Applied multistep bioinformatics revealed 473 differentially expressed genes (DEGs): 198 upregulated and 275 downregulated. Functional Gene Ontology annotated 347 DEGs into 27 biological processes, 324 to the 11 cellular components and 346 to the 2 molecular functions categories. In the signaling pathway analysis, KEGG 'protein processing in endoplasmic reticulum' was identified for the mRNAs modulated during PE. The same KEGG pathway was also exposed by 8 differentially alternative splicing genes. Within single nucleotide variants, the 61 allele-specific expression variants were localised in the vicinity of the genes that belong to the cellular components of the 'endoplasmic reticulum'. The discovered allele-specific genes were also classified as signatures of the cardiovascular system.

CONCLUSIONS

The findings of this research provide the first thorough investigation of the changes in the gene expression profile of PA affected by an embolus. Evidence from this study suggests that the disturbed homeostasis in the biosynthesis of proteins in the endoplasmic reticulum plays a major role in the pathogenesis of PE.

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.

Endovascular Venous Stenosis and Thrombosis Large Animal Model: angiographic, histological, and biomechanical characterization

PURPOSE

Characterize an ovine endovascular radiofrequency ablation based venous stenosis and thrombosis model for studying venous biomechanics and response to intervention.

MATERIALS AND METHODS

Unilateral short-segment (n= 2) or long-segment (n = 6) iliac vein stenoses were created in eight adult sheep using an endovenous radiofrequency (RF) ablation technique. Angiographic assessment was performed at baseline, immediately after venous stenosis creation, and after 2-week (n = 6) or 3-month (n = 2) survival. Stenosed iliac veins and contralateral healthy controls were harvested for histological and biomechanical assessment.

RESULTS

At follow-up, the short-segment RF ablation group showed stable stenosis without occlusion. The long-segment group showed complete venous occlusion/thrombosis with formation of collateral veins. Stenosed veins showed significant wall thickening (0.28 mm vs 0.16 mm; p = 0.0175) and confluent collagen deposition compared to healthy controls. Subacute non-adherent thrombi were apparent at 2 weeks, which were replaced by fibrous luminal obliteration with channels of recanalization at 3 months. Stenosed veins demonstrated increased longitudinal stiffness (448.5 ± 5.4 kPa vs. 314.6 ± 1.5 kPa, p < 0.0001) and decreased circumferential stiffness (140.8 ± 2.6 kPa vs. 246.0 ± 1.6 kPa, p < 0.0001) compared to healthy controls.

CONCLUSION

Endovenous radiofrequency ablation is a reliable technique for creating venous stenosis and thrombosis in a large animal model with histological and biomechanical attributes similar to those seen in humans. This platform can facilitate understanding of venous biomechanics and testing of venous specific devices and interventions.

A New Experimental Porcine Model of Venous Thromboembolism

Venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE), is a severe disease affecting the human venous system, accompanied by high morbidity and mortality rates. The aim of the study was to establish a new porcine VTE model based on the formation of the thrombus in vivo. The study was performed on 10 castrated male pigs: thrombus was formed in each closed femoral vein and then successfully released from the right femoral vein into the circulation of animals. In six pigs PE was confirmed via both computed tomography pulmonary angiography and an autopsy. Our research presents a novel experimental porcine model of VTE that involves inducing DVT and PE in the same animal in vivo, making it suitable for advanced clinical research and testing of future therapies.

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.

Fatal Ovarian Hemorrhage Associated With Anticoagulation Therapy in a Yucatan Mini-Pig Following Venous Stent Implantation

Swine models are commonly utilized in endovascular research for development of intravascular interventions and medical device development. As part of a pilot study for a venous vascular stent device, a 5-year-old female Yucatan mini-pig underwent bilateral external iliac vein stent placement under general anesthesia. To reduce thrombotic complications by reduction of thrombus formation on wires, sheaths, and catheters, the pig was heparinized with a total of 300 IU/kg of heparin, establishing an activated clotting time (ACT) of 436 s. The ACT had returned to below 200 s by the end of the procedure. To prevent postoperative thrombosis, the pig received an anticoagulation therapy protocol consisting of enoxaparin, clopidogrel, and aspirin. There were no complications during the immediate postoperative period. However, the pig died 4 days after surgery. Necropsy established the cause of death as abdominal exsanguination due to severe, acute, intra-ovarian hemorrhage, most likely related to ovulation. Life-threatening ovarian hemorrhage is occasionally seen in women with congenital or acquired bleeding disorders; to our knowledge this is the first report of fatal ovarian hemorrhage in an animal enrolled in a pre-clinical research trial.

By word of mouse: using animal models in venous thrombosis research

Deep vein thrombosis (DVT) is a disease with high prevalence and morbidity. It can lead to pulmonary embolism with severe respiratory insufficiency and risk of death. Mechanisms behind all stages of DVT, such as thrombosis commencement, propagation, and resolution, remain incompletely understood. Animal models represent an invaluable tool to explore these problems and identify new targets for DVT prevention and treatment. In this review, we discuss existing models of venous thrombosis, their advantages and disadvantages, and applicability to studying different aspects of DVT pathophysiology. We also speculate about requirements for an "ideal model" that would best recapitulate features of human DVT and discuss readouts of various models.

Animal models of venous thrombosis

Venous thrombosis (VT) is a prevalent clinical condition with significant adverse sequela or mortality. Anticoagulation and pharmacologic or pharmacomechanical thrombolytic therapies are the mainstays of VT treatment. An understanding of thrombosis biology will allow for more effective VT-tailored diagnosis and therapy. In vivo models of thrombosis provide indispensable tools to study the pathogenesis of thrombus formation and to evaluate novel therapeutic or preventive adjuncts for VT management or prevention. In this article, we review the most prominent in vivo models of VT created in rodents and swine species and outline how each model can serve as a useful tool to promote our understanding of VT pathogenesis and to examine novel therapies.

Two swine models of iliac vein occlusion: Which form most contributes to venous thrombosis?

OBJECTIVES

In the present study, we establish two swine models of iliac vein occlusion (IVO) with spontaneous thrombosis to understand the mechanisms linking IVO and thrombosis.

METHODS

Two IVO models were established in 12 swine either by ligating the common iliac vein (CIVO) or both the common and external iliac veins (CEIVO). Venography was performed to assess each model and the associated thrombosis. Invasive blood pressure was also measured, and the vessels were examined histologically to analyse the pathological changes after ligation.

RESULTS

On venography, the CIVO model showed common iliac vein (CIV) occlusion and reflux in the collateral veins whereas the CEIVO model showed occlusion in the CIV and external iliac vein (EIV), stasis in the EIV, and decreased collateral vasculature on venography. Thrombosis was only observed in the CEIVO model, which was with significantly higher venous blood pressure in the EIV and with significantly more thickened venous wall with lymphocytic infiltration histologically.

CONCLUSIONS

Two IVO models can be feasibly and reliably established in swine. The CEIVO model had a higher prevalence of thrombosis than the CIVO model. This CEIVO model produces comparatively less collateral drainage and greater inflammation that can contribute to the thrombosis prone to this type of model.

Aspectos clínicos, ultra-sonográficos e venográficos da tromboflebite jugular experimental em equinos

A tromboflebite jugular ocorre frequentemente em equinos, decorrendo geralmente de processos mórbidos associados à iatrogenia, podendo levar a perda de função, edema cefálico, diminuição do desempenho atlético e ainda causar o óbito. Esta enfermidade nos equinos apesar de frequente é pouco conhecida quanto à sua evolução e tratamentos. O objetivo deste trabalho foi avaliar a evolução da tromboflebite jugular experimental em equinos, quanto às alterações clínicas e estruturais envolvidas na enfermidade, observando-se os aspectos clínicos, ultra-sonográficos e venográficos no contexto do trombo e do vaso, quanto à possibilidade de recanalização do trombo produzido e da vascularização compensatória. A tromboflebite da veia jugular foi induzida, unilateralmente, em 05 equinos nos quais previamente à indução da tromboflebite e diariamente após foram observadas manifestações clínicas e realizados exames ultra-sonográficos. Venografias foram feitas nos momentos pré-indução, na indução e a cada seis dias após a indução da tromboflebite, verificando-se a recanalização do trombo oclusivo e a presença de vasos na drenagem sanguínea compensatória. Observou-se a ocorrência de edema moderado das regiões parotídea, massetérica e supra-orbitária e discreto edema submandibular que reduziram até o 6º dia, permanecendo apenas discreto aumento parotídeo. O ingurgitamento da jugular cranial a região da indução permaneceu durante todo o período de avaliação. A porção caudal à tromboflebite mostrou ingurgitamento frente ao garrote na entrada do tórax desde o primeiro dia após a indução. Os exames ultra-sonográficos mostraram formação de trombo oclusivo total durante todo o período de observação em 3 animais e o restabelecimento parcial do fluxo na jugular em 2 animais e a presença de vasos colaterais conduzindo o sangue da porção cranial para a porção caudal à obstrução. As venografias revelaram fluxo sanguíneo "linear" normal no momento pré-operatório, constatando nos momentos pós-operatórios a presença oclusiva do trombo, com o contraste preenchendo os vasos tributários compensatórios direcionados à porção caudal à oclusão da veia ou ainda estagnado cranialmente ao trombo. Conclui-se que a trombose oclusiva na tromboflebite jugular experimental e unilateral sofre recanalização e compensação vascular por vasos tributários de drenagem, com redução gradativa dos sinais decorrentes da estase sanguínea de retorno, especificamente as regiões cefálicas com edema. Estudos envolvendo a tromboflebite jugular nos equinos devem evoluir nos aspectos experimental e clínico.

Noninvasive treatment of deep venous thrombosis using pulsed ultrasound cavitation therapy (histotripsy) in a porcine model

PURPOSE

This study evaluated histotripsy as a noninvasive, image-guided method of thrombolysis in a porcine model of deep vein thrombosis. Histotripsy therapy uses short, high-intensity, focused ultrasound pulses to cause mechanical breakdown of targeted soft tissue by acoustic cavitation, which is guided by real-time ultrasound imaging. This is an in vivo feasibility study of histotripsy thrombolysis.

METHODS AND MATERIALS

Acute thrombi were formed in the femoral vein of juvenile pigs weighing 30-40 kg by balloon occlusion with two catheters and thrombin infusion. A 10-cm-diameter 1-MHz focused transducer was used for therapy. An 8-MHz ultrasound imager was used to align the clot with the therapy focus. Therapy consisted of five cycle pulses delivered at a rate of 1 kHz and peak negative pressure between 14 and 19 MPa. The focus was scanned along the long axis of the vessel to treat the entire visible clot during ultrasound exposure. The targeted region identified by a hyperechoic cavitation bubble cloud was visualized via ultrasound during treatment.

RESULTS

Thrombus breakdown was apparent as a decrease in echogenicity within the vessel in 10 of 12 cases and in 7 cases improved flow through the vein as measured by color Doppler. Vessel histology found denudation of vascular endothelium and small pockets of hemorrhage in the vessel adventitia and underlying muscle and fatty tissue, but perforation of the vessel wall was never observed.

CONCLUSIONS

The results indicate histotripsy has potential for development as a noninvasive treatment for deep vein thrombosis.

In vivo veritas: Thrombosis mechanisms in animal models

Experimental models have enhanced our understanding of atherothrombosis pathophysiology and have played a major role in the search for adequate therapeutic interventions. Various animal models have been developed to simulate thrombosis and to study in vivo parameters related to hemodynamics and rheology that lead to thrombogenesis. Although no model completely mimics the human condition, much can be learned from existing models about specific biologic processes in disease causation and therapeutic intervention. In general, large animals such as pigs and monkeys have been better suited to study atherosclerosis and arterial and venous thrombosis than smaller species such as rats, rabbits, and dogs. On the other hand, mouse models of arterial and venous thrombosis have attracted increasing interest over the past two decades, owing to direct availability of a growing number of genetically modified mice, improved technical feasibility, standardization of new models of local thrombosis, and low maintenance costs. To simulate rupture of an atherosclerotic plaque, models of arterial thrombosis often involve vascular injury, which can be achieved by several means. There is no animal model that is sufficiently tall, that can mimic the ability of humans to walk upright, and that possesses the calf muscle pump that plays an important role in human venous hemodynamics. A number of spontaneous or genetically engineered animals with overexpression or deletion of various elements in the coagulation, platelet, and fibrinolysis pathways are now available. These animal models can replicate important aspects of thrombosis in humans, and provide a valuable resource in the development of novel concepts of disease mechanisms in human patients.

Trombectomia com cateter de Fogarty no tratamento da tromboflebite jugular experimental em eqüinos

Trombose da veia jugular é problema freqüente na medicina eqüina, implicando muitas vezes em conseqüências fatais. O objetivo deste trabalho foi avaliar em eqüinos a aplicabilidade da trombectomia com cateter de Fogarty, técnica rotineiramente empregada pela medicina humana, no restabelecimento da perviedade vascular. Foram utilizados 10 eqüinos divididos em dois grupos de cinco animais, em que se induziu a trombose da veia jugular direita, através do acesso cirúrgico à veia e aplicação de sutura estenosante e injeção de glicose a 50%. No grupo controle avaliou-se a evolução da tromboflebite sem qualquer tipo de intervenção terapêutica. Os animais do grupo tratado foram submetidos à trombectomia com cateter de Fogarty. Foram avaliados os parâmetros clínicos gerais, regionais, ultra-sonográficos e angiográficos, nos momentos pré-indução (M-PRÉ), indução da trombose (MTI) e 10 dias de evolução da trombose (M10). A técnica empregada induziu a tromboflebite, que obstruiu completamente um segmento da veia jugular de todos os animais. Os animais do grupo controle mantiveram os trombos obstruindo totalmente o lume vascular até o final do período de avaliação, sendo que avaliações regionais mostraram principalmente o edema parotídeo e o ingurgitamento vascular, cranial à tromboflebite da veia jugular. O grupo tratado apresentou as veias jugulares pérvias ao final do experimento, confirmadas pelos exames ultra-sonográficos e angiográficos, com remissão total dos sinais clínicos. Concluiu-se que a técnica da trombectomia com cateter de Fogarty foi eficiente na desobstrução da veia jugular submetida à trombose experimental.

Rheolytic pharmacomechanical thrombectomy in experimental chronic deep vein thrombosis: effect of L-arginine on thrombogenicity and endothelial vasomotor function

PURPOSE

Endovascular removal of intravascular thrombus using the AngioJet rheolytic thrombectomy (RT) system has been shown to be clinically effective. This system also permits the concomitant infusion of thrombolytic agent followed by thrombectomy, thus creating a novel strategy known as pharmacomechanical thrombectomy (PMT). Although these interventions have gained wide clinical application, little is known regarding the vessel wall response following thrombectomy therapy. The aims of this study were to assess the effect of thrombectomy interventions on endothelial function in a porcine model of deep venous thrombosis (DVT) and to evaluate the effect of nitric oxide (NO) precursor L-arginine on endothelial function following thrombectomy therapy.

METHODS

Deep vein thrombosis was created in bilateral iliac veins by deploying a self-expanding stent-graft incorporating an intraluminal stenosis from a groin approach. Five pigs underwent sham operation. Following 14 days of DVT, animals were randomized to three groups: the first group received RT treatment (RT group, n = 5); the second group received pharmacomechanical thrombectomy (PMT) with tissue plasminogen activator (alteplase 10 mg; PMT group, n = 5); and the third group received PMT with tPA plus intravenous L-arginine (20 mmol/l) (arginine group, n = 5). Iliac vein patency was evaluated by venography and intravascular ultrasound at 1 week. Nitric oxide level was determined by a chemiluminescent assay of the nitrite/nitrate metabolites (NO(x)). Thrombogenicity was evaluated by radiolabeled platelet and fibrin deposition. Veins were harvested and evaluated with light microscopy and scanning electron microscopy (SEM). Endothelial function was evaluated using organ chamber analysis.

RESULTS

The luminal areas in the sham, RT, PMT, and arginine groups were 34 +/- 10 mm(2), 21 +/- 13 mm(2), 35 +/- 18 mm(2), and 37 +/- 16 mm(2), respectively. All iliac veins remained patent at 2 weeks. No difference in endothelial cell structure was observed between the three treatment groups by means of light microscopic or SEM examination. A decrease in platelet deposition occurred in the arginine group compared to the RT and PMT groups (P < 0.05). The arginine group also showed a greater endothelium-dependent relaxation compared to the RT or PMT groups in response to A23187, bradykinin, and ADP (P < 0.05). Local NO(x) level was higher in the arginine group than in the RT or PMT group (2.6 +/- 0.6 micromol/l versus 0.3 +/- 0.1 micromol/l and 0.3 +/- 0.2 micromol/l; P < 0.01).

CONCLUSIONS

AngioJet RT and PMT interventions resulted in similar attenuated endothelium-dependent vasoreactivity and morphologic effect. L-Arginine supplementation preserves endothelial vasoreactivity and reduces platelet deposition following PMT in iliac DVT. Additionally, L-arginine enhances NO production at sites of venous thrombosis. The NO precursor L-arginine may have a therapeutic potential in preserving endothelial function following mechanical thrombectomy.

Relation of Ultrasound Morphologic Characteristics of Central Pulmonary Artery Thromboemboli to Their Ex Vivo Lysibility

BACKGROUND

Ultrasound morphology of massive central pulmonary artery thromboemboli (TE) is an independent predictor of 30-day mortality. The aim of this study was to asses ex vivo lysibility of morphologically different TE.

METHODS

Forty-five central pulmonary artery TE, collected at autopsies, were divided into hypoechoic (group A) and hyperechoic (group B) categories. TE were lysed with alteplase in a perfusing system simulating pulmonary circulation for 1 hour.

RESULTS

The grey scale mean of thrombi in group B was higher compared with group A (64 +/- 7 vs. 38 +/- 7, respectively, P < .01). Spontaneous lysis in group A did not differ compared with group B (2.2% +/- 0.5% vs. 2.1% +/- 0.4%, P = .4). After incubation with alteplase, the weight of TE was reduced more in group A than in group B (16% +/- 2% vs. 11% +/- 2%, P < .001). The grey scale mean negatively correlated with the percentage of TE weight reduction (0.768) (P < .001).

CONCLUSION

Ultrasound morphology of TE from central pulmonary arteries correlates significantly with ex vivo lysibility. Hypoechoic TE are more susceptible to thrombolysis than hyperechoic TE.

Laparoscopic ligation of the infrarenal vena cava in combination with transfemoral thrombin infusion: a new animal model of chronic deep venous thrombosis

OBJECTIVE

We describe a new technique to create an animal model of chronic venous thrombosis. The morphological and histological properties of the resulting thrombi are described.

METHODS

Thirteen pigs underwent laparoscopic ligation of the infrarenal vena cava in combination with transfemoral thrombin infusion. After 1, 3, 6, 9, 12 and 15 days, respectively, two animals were killed and the thrombosed vein segments were explanted. After recording their weight and dimensions, the thrombi underwent histological examination by light microscopy.

RESULTS

In all 13 cases, the procedure was completed laparoscopically and all 13 animals survived the procedure. While 12 pigs (92%) had an uneventful postoperative course, one animal died on the first postoperative night of an unknown cause. Autopsy revealed correct placing of the ligature with occlusive thrombosis of the inferior vena cava and the iliac veins in 12 animals, in one animal the ligature had been incorrectly placed around the origin of the right iliac vein with thrombosis limited to that vessel. Histological evaluation demonstrated mixed thrombi that showed increasing signs of organisation with advancing age.

CONCLUSIONS

Laparoscopic ligation of the infrarenal vena cava in combination with transfemoral thrombin infusion is a safe and reliable way to produce chronic venous thrombosis in an animal model. The resulting thrombi are comparable to human deep venous thrombosis in terms of extent, size and organisation process.

Morphologic characteristics of central pulmonary thromboemboli predict haemodynamic response in massive pulmonary embolism

OBJECTIVE

On hospital admission, the morphology of the central pulmonary artery thromboemboli is an independent predictor of 30-day mortality in patients with massive pulmonary embolism (MPE). This may be due to the differential susceptibility of thromboemboli to thrombolysis. The aim of this study was to assess haemodynamic response to treatment in patients with MPE and morphologically different thromboemboli.

DESIGN

Prospective observational study.

SETTING

An 11-bed closed medical ICU at a 860-bed community general hospital.

PATIENTS

Twelve consecutive patients with shock or hypotension due to MPE and central pulmonary thromboemboli detected by transesophageal echocardiography who were treated with thrombolysis between January 2000 through April 2002.

PROCEDURES

Patients were divided into two groups according to the characteristics of detected central pulmonary thromboemboli: group 1, thrombi with one or more long, mobile parts; and group 2, immobile thrombi. Urokinase infusion was terminated when mixed venous oxygen saturation was stabilized above 60% for 15 min.

RESULTS

At 2 h, the total pulmonary vascular resistance index was reduced more in group 1 than group 2 [from 27+/-12 mmHg/(l.min.m(2)) to 14+/-6 mmHg/(l.min.m(2)) (-52%) vs 27+/-8 mmHg/(l.min.m(2)) to 23+/-10 mmHg/(l.min.m(2)) (-15%), respectively, P=0.04]. In group 1 thrombolysis was terminated earlier than group 2 (89+/-40 min vs 210+/-62 min, respectively, P= 0.0024). The cumulative dose of urokinase used in group 1 was lower than group 2 (1.7+/-0.3 M i.u. vs 2.7+/-0.5 M i.u., respectively, P= 0.023).

CONCLUSION

Haemodynamic stabilization is achieved faster in patients with mobile central thromboemboli detected by transesophageal echocardiography during MPE.

L-arginine improves endothelial vasoreactivity and reduces thrombogenicity after thrombolysis in experimental deep venous thrombosis

PURPOSE

Nitric oxide (NO) is important in regulation of platelet aggregation, endothelial function, and intravascular thrombosis. The purposes of this study were to assess the effect of thrombolysis on endothelial function in a porcine model of deep venous thrombosis (DVT) and to evaluate the effect of NO precursor l-arginine on endothelial function after thrombolytic therapy.

METHODS

DVT was created in bilateral iliac veins by deploying a self-expanding stent-graft that incorporated an intraluminal stenosis, from a groin approach. Five pigs underwent sham operation. After 7 days of DVT, animals were randomized to three groups: saline pulse-spray (saline group, n = 5), thrombolytic pulse-spray with tissue plasminogen activator (alteplase, 8 mg; t-PA group, n = 5), and thrombolytic pulse-spray plus intravenous l-arginine (20 mmol/L; arginine group, n = 5). At 2 weeks iliac vein patency was evaluated at venography and intravascular ultrasound scanning. NO level was determined with a chemiluminescent assay of the nitrite and nitrate metabolites (NO(x)). Thrombogenicity was evaluated with radiolabeled platelet and fibrin deposition. Veins were harvested and evaluated with light microscopy and scanning electron microscopy. Endothelial function was evaluated with organ chamber analysis.

RESULTS

All iliac veins remained patent at 2 weeks. The luminal areas in the sham, saline, t-PA, and arginine groups were 53 +/- 23 mm(2), 14 +/- 11 mm(2), 34 +/- 19 mm(2), and 42 +/- 21 mm(2), respectively. No difference in endothelial cell structure was observed between the three treatment groups at light microscopy or scanning electron microscopy. Although no difference in fibrin deposition was noted among the three treatment groups, decreased platelet deposition occurred in the arginine group compared with the saline or t-PA groups (P <.05). The arginine group showed greater endothelial-dependent relaxation compared with the t-PA or saline groups (73% +/- 23% vs 49% +/- 18% and 32% +/- 21%; P <.05). Local NO(x) level in the arginine group was correspondingly higher compared with the saline or t-PA groups (1.8 +/- 0.3 micromol/L vs 0.3 +/- 0.05 micromol/L and 0.2 +/- 0.04 micromol/L; P <.05).

CONCLUSIONS

NO precursor l-arginine supplementation enhances NO production at sites of venous thrombosis. Moreover, l-arginine preserves endothelial vasoreactivity and reduces platelet deposition after thrombolysis in iliac DVT. These data suggest that l-arginine may preserve endothelial function after thrombolysis and may reduce the likelihood of postthrombotic syndrome.

A percutaneous approach to deep venous valve insufficiency with a new self-expanding venous frame valve

PURPOSE

To ascertain if a percutaneously delivered venous valve bioprosthesis (PVVB) can be implanted in the porcine venous system and function without complications.

METHODS

The PVVB is a glutaraldehyde-preserved, valve-bearing venous xenograft sutured inside a memory-coded nitinol frame (diameter 10, 12, or 14 mm). In 10 50-kg pigs, the external jugular vein was exposed, and a 16-F introducer sheath was positioned in the common iliac vein. One PVVB was inserted and deployed in each iliac vein under fluoroscopic control. After PVVB implantation, all animals were randomly given either vitamin K antagonists (1-2 mg/d) (group I) or a combination of aspirin (150 mg/d) and clopidogrel (75 mg/d) (group II), which were shown in a preliminary pilot study to be the most effective anticoagulation regimens in the pig model. Ascending and descending completion phlebograms were performed. PVVBs were evaluated with phlebography at 4 weeks to assess patency and competence; all PVVBs were explanted and processed for histological analysis.

RESULTS

In 8 animals, the PVVB was successfully deployed in both the left and right iliac veins. In 2 pigs, only 1 PVVB was inserted due to vascular anomalies. Completion phlebography demonstrated 18 patent and competent valves. At 2 weeks, bleeding complications occurred in 3 group I pigs; all 5 animals were terminated to prevent further complications. Of the 8 valves in this group, 7 were patent (3 competent) by phlebography; 1 PVVB had migrated due to known undersizing of the stent frame. At 4 weeks, group II (5 pigs, 10 valves) analysis revealed 5 patent (3 competent) valves; no bleeding complications occurred in this group. Histology showed thrombosis as the cause of occlusion in all 5 non-patent valves from group II.

CONCLUSIONS

Deployment of a glutaraldehyde-fixed bovine vein sutured to a self-expanding nitinol stent in the porcine iliac vein is technically feasible. Development of a venous bioprosthesis that can be placed percutaneously may have important clinical applications as an endovascular treatment for chronic venous insufficiency when it is due to valvular incompetence.

Principle mechanisms underlying venous thromboembolism: epidemiology, risk factors, pathophysiology and pathogenesis

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are distinct but related aspects of the same dynamic disease process known as venous thromboembolism (VTE). An estimated 200,000 new cases occur in the United States every year, including 94,000 with PE, resulting in an incidence of 23 per 100,000 patients per year-cases. Without treatment, pulmonary embolism is associated with a mortality rate of approximately 30%, causing nearly 50,000 deaths per year. Moreover, based on post-mortem studies, two-thirds of the patients with pulmonary emboli remain undiagnosed. Clinically, PE may present as (1) isolated dyspnea, (2) pleuritic pain and/or hemoptysis, and (3) circulatory collapse. However, clinical history and examination can be notoriously misleading in reaching a diagnosis. A number of acquired etiologic risk factors (predispositions) are associated with a tendency to develop VTE. These include increasing age, immobilization, surgery, trauma, hospital or nursing home confinement, malignancy, neurologic disease with extremity paresis, as well as certain types of oral contraception and hormone replacement therapy. In addition, a variety of genetic risk factors, such as factor V Leiden, protein S or C deficiency have also been identified. However, in at least half of the instances, no predisposing factors can be identified (idiopathic PE). In the majority of cases thromboemboli originate in the deep veins of the calf or pelvis. The pathogenic conditions for VTE comprise a triad of factors and include (1) venous stasis, (2) hypercoagulable states, and (3) vascular endothelium injury. Occlusion of pulmonary arteries has variable and transient clinical and pathophysiologic consequences, involving both mechanical and reflex effects of vascular occlusion with a consecutive perfusion defect as well as the release of vasoactive and other inflammatory mediators. The objectives of this article are to present an overview of the etiologic and pathogenic factors promoting VTE as well as the pathophysiologic and inflammatory processes following PE.

Early results of thrombolysis vs anticoagulation in iliofemoral venous thrombosis. A randomised clinical trial

OBJECTIVE

catheter directed thrombolysis has been advocated for complete and rapid dissolution of iliofemoral deep venous thrombosis (DVT). The aim of our study is to compare, in a randomised trial, local thrombolysis and anticoagulation with anticoagulation alone in patients with iliofemoral DVT.

METHODS

a consecutive series of 35 eligible patients, were randomised to either catheter directed thrombolysis followed by anticoagulation or to anticoagulation alone. Clot lysis and deep venous reflux were assessed with ultrasound duplex and plethysmography after 6 months.

RESULTS

complete data were available in the 18 and 17 patients randomised to thrombolysis and anticoagulation, respectively. At 6 months, patency rate was better in cases treated with thrombolysis [13/18 (72%) vs 2/17 (12%), p < 0.001]. Venous reflux was higher in-patients treated with anticoagulant [7 patients (41%) vs 2 (11%), p = 0.04].

CONCLUSION

in the short-term patients treated with catheter directed thrombolysis obtained better patency and competence than those treated with standard anticoagulation.

Impact of morphologic characteristics of central pulmonary thromboemboli in massive pulmonary embolism

STUDY OBJECTIVE

To assess the impact of morphologically different central pulmonary artery thromboemboli in patients with massive pulmonary emboli (MPEs) on short-term outcome.

DESIGN

A prospective registry of consecutive patients.

SETTING

An 11-bed closed medical ICU at a 860-bed community general hospital

PATIENTS

Forty-seven patients with shock or hypotension due to MPE and central pulmonary thromboemboli detected by transesophageal echocardiography who were treated with thrombolysis between January 1994 and April 2000.

PROCEDURES

Patients were divided into two groups according to the following characteristics of the detected thromboemboli: group 1, thrombi with one or more long, mobile parts; and group 2, immobile thrombi. Right heart catheterization was performed.

RESULTS

The incidence of both types of thromboemboli was comparable. Groups 1 and 2 showed no differences in demographic data, risk factors for pulmonary embolism, length of preceding clinical symptoms, percentage of patients in shock, hemodynamic variables, serum lactate levels on hospital admission, and treatment. Seven fatal cases due to obstructive shock and right heart failure were present in group 2, but none were present in group 1 (7 of 23 patients vs 0 of 24 patients, respectively; p < 0.05). At 12 h, the cardiac index was lower in group 2 than in group 1 (2.6 +/- 1.0 vs 3.1 +/- 0.9 L/min/m(2), respectively; p < 0.05), and the central venous pressure (15.0 +/- 6.2 vs 12.5 +/- 3.7 mm Hg, respectively; p < 0.05) and total pulmonary resistance (12.9 +/- 5.9 vs 8.6 +/- 2.7 mm Hg/L/min/m(2), respectively; p < 0.001) were higher in group 2 compared to group 1. On hospital admission, inclusion in group 2 (p < 0.03; hazard ratio, 9.53; 95% confidence interval [CI], 1.19 to 76.47) and preexisting chronic medical or neurologic disease (p < 0.01; hazard ratio, 16.4; 95% CI, 1.97 to 136.3) were independent predictors of 30-day mortality.

CONCLUSION

On hospital admission, morphology of the thromboemboli and the presence of pre-existing chronic medical or neurologic disease are independent predictors of 30-day mortality. Patients with immobile central pulmonary thromboemboli have a worse short-term outcome than those with mobile central pulmonary thromboemboli.