Thrombosis with outflow obstruction delays thrombolysis and results in chronic wall thickening of rat veins

Plasmin and Matrix Metalloproteinase System in Deep Venous Thrombosis Resolution

Deep venous thrombosis (DVT) is a common event in hospitalized medical and surgical patients. Outside of anticoagulation, few good options exist for decreasing the vein wall damage that results after natural thrombolysis. DVT resolution is complex and involves chemokines, leukocytes, and native vein wall cells. Herein some aspects of DVT resolution related to the intersection of inflammation, the plasminogen and matrix metalloproteinase systems, and their respective inhibitors are reviewed. Ultimately, better knowledge of these natural thrombolytic systems may allow local, directed, and specific acceleration of DVT resolution and decreased vein wall damage.

Thrombus age is ideally measured by history or MRV prior to thrombus removal

Many factors are known to be important in order to achieve optimal results after thrombus removal for iliofemoral DVT. Not much is published in the literature about timing the treatment, though many guidelines recommend treatment within 14 days. This time span lies within the phrase of acute DVT according to the definition given in many reporting standards. This article will highlight the value of information acquired from patients directly regarding onset of symptoms versus information acquired from imaging with the purpose of a more precise selection of patients for catheter-directed thrombolysis for iliofemoral DVT. What is the value of clinical information acquired from patients and does the information from imaging have additional value?

Catheter-directed thrombolysis with a continuous infusion of low-dose urokinase for non-acute deep venous thrombosis of the lower extremity

OBJECTIVE

We wanted to evaluate the feasibility of catheter-directed thrombolysis with a continuous infusion of low-dose urokinase for treating non-acute (less than 14 days) deep venous thrombosis of the lower extremity.

MATERIALS AND METHODS

The clinical data of 110 patients who were treated by catheter-directed thrombolysis with a continuous infusion of low-dose urokinase for lower extremity deep venous thrombosis was analysed. Adjunctive angioplasty or/and stenting was performed for the residual stenosis. Venous recanalization was graded by pre- and post-treatment venography. Follow-up was performed by clinical evaluation and Doppler ultrasound.

RESULTS

A total of 112 limbs with deep venous thrombosis with a mean symptom duration of 22.7 days (range: 15-38 days) were treated with a urokinase infusion (mean: 3.5 million IU) for a mean of 196 hours. After thrombolysis, stent placement was performed in 25 iliac vein lesions and percutaneous angioplasty (PTA) alone was done in five iliac veins. Clinically significant recanalization was achieved in 81% (90 of 112) of the treated limbs; complete recanalization was achieved in 28% (31 of 112) and partial recanalization was achieved in 53% (59 of 112). Minor bleeding occurred in 14 (13%) patients, but none of the patients suffered from major bleeding or symptomatic pulmonary embolism. During follow-up (mean: 15.2 months, range: 3-24 months), the veins were patent in 74 (67%) limbs. Thirty seven limbs (32%) showed progression of the stenosis with luminal narrowing more than 50%, including three with rethrombosis, while one revealed an asymptomatic iliac vein occlusion; 25 limbs (22%) developed mild post-thrombotic syndrome, and none had severe post-thrombotic syndrome. Valvular reflux occurred in 24 (21%) limbs.

CONCLUSION

Catheter-directed thrombolysis with a continuous infusion of low-dose urokinase combined with adjunctive iliac vein stenting is safe and effective for removal of the clot burden and for restoration of the venous flow in patients with non-acute lower extremity deep venous thrombosis.

Plasmin inhibition increases MMP-9 activity and decreases vein wall stiffness during venous thrombosis resolution

INTRODUCTION

Deep venous thrombosis (DVT) resolution involves the plasmin and the matrix metalloproteinase (MMP) system. This study tested the hypothesis that pharmacological inhibition of the plasmin system would impair DVT resolution and worsen vein wall damage.

METHODS

A rat model of stasis DVT by inferior vena cava (IVC) ligation was performed with intravenous control saline or aprotinin (AP; 2.8 mg/kg at operation), and harvest of thrombosed IVC at 7 days. After laser Doppler imaging, DVT were separated and weighed, and vein wall stiffness was assessed by tensiometry. Thrombus and vein wall tissue analysis included total collagen by colorimetric assay, cytokines, chemokines, and d-dimer by ELISA, urokinase-plasminogen activator (uPA), and plasminogen activator inhibitor-1 (PAI-1) by immuno-blotting, MMP-2 and -9 by zymography, and neutrophil (PMN) and monocyte (ED-1) leukocytes by immunohistochemistry.

RESULTS

DVT weights were 2-fold greater in the AP-treated rats (P < 0.05), but no significant differences in thrombus perfusion, collagen, or d-dimer levels were found. Vein wall stiffness was reduced 50% (P < 0.05), suggesting less biomechanical injury. The total vein wall MMP-9 was increased (P < 0.05) 5-fold in the AP group compared with controls, while MMP-2 was elevated but did not reach significance. No difference was found in vein wall tumor necrosis factor-alpha, tissue growth factor-beta, vein wall or thrombus monocytes, PMN, or uPA/PAI-1 ratio between groups.

DISCUSSION

AP inhibition of the plasmin system was associated with larger thrombi but less vein wall injury, but no difference in other measures of resolution, possibly because of increased vein wall MMP-9 activity. These data suggest an important redundant mechanism for DVT resolution.

Adventitial remodeling with increased matrix metalloproteinase-2 activity in a porcine arteriovenous polytetrafluoroethylene grafts

BACKGROUND

We hypothesized the source of early proliferating cells contributing to venous stenosis formation in a porcine hemodialysis grafts is the adventitia and media, and migration of these cells is greatest within the first two weeks following graft placement, resulting in increased matrix metalloproteinase-2 (MMP-2) activity.

METHODS

Polytetrafluoroethylene grafts from the iliac artery to the ipsilateral iliac vein were placed in 23 pigs and 5-Bromo-2'-deoxyuridine (BrdU) was given at 24 and 48 hours after surgery to assess cell proliferation and migration. Angiography and magnetic resonance angiography was performed. Animals were euthanized on day three (N= 6), day seven, (N= 5), day 14 (N= 6), and days 19 to 26 (N= 6) after graft placement, and stenotic tissue and unaffected contralateral iliac vein were removed for zymography and immunostaining.

RESULTS

Migration of cells derived from the adventitia and media peaked at day 14. Adventitial diameter of the stenotic vein decreased, while the intima to media ratio increased. MMP-2 activity peaks at day seven in the adventitia and days 19 to 26 in the intima.

CONCLUSION

These results confirm our hypothesis that the source of cells resulting in venous stenosis formation is derived from the adventitia and media, with cell migration being greatest within the first two weeks after graft placement with translocation of these cells into the intima at four weeks. MMP-2 activity peaks at day seven in the adventitia and again at days 19 to 26 in the intima. A key to limiting venous stenosis formation may lie in inhibiting MMP-2 by adventitial and medial targeting.

The role of inflammation in early and late venous thrombosis: Are there clinical implications?

Venous thrombosis is associated with a significant inflammatory response. Inflammatory cells, adhesion molecules (especially selectins), cytokines, and procoagulant microparticles appear to be associated with the thrombogenic process. Once thrombus forms, inflammatory cells are important to thrombus resolution along with fibrinolytic agents and proinflammatory mediators. Collagen and elastin breakdown by the DVT renders the vein wall stiff and non-compliant. Rapid and complete thrombus resolution should lessen vein wall damage and lessen or prevent the development of chronic venous insufficiency. Understanding the basic biology of thrombogenesis and thrombus resolution is important, as novel therapies to both prevent and treat venous thrombosis and hasten thrombus resolution should result from a better understanding of the basic biological mechanisms.

Role of Platelet Activation in Catheter-Induced Vascular Wall Injury

PURPOSE

To investigate the role of smooth muscle cell (SMC) response and platelet activation in peripheral venous catheterization using a model of catheter injury associated with thrombocytopenic treatment.

METHODS

Silicon elastic catheters were inserted into New Zealand White rabbit external jugular veins from 24 hours to 60 days. Immunocytochemical procedures with antibodies to differentiation markers specific for SMCs, myofibroblasts, and endothelial cells were used to ascertain the phenotypic features of injured venous SMCs and the tissue sleeve formed around the catheter. Thrombocytopenia was induced in rabbits by busulfan treatment and the effect on catheter injury development examined after 15 days. The putative direct effect of this drug on the venous SMC proliferation, migration, and differentiation was assayed in vitro for 48 hours.

RESULTS

Catheter injury is characterized by the progressive formation of (1) a neointima, containing differentiating SMCs, which are derived from the media and adventitial layer, and (2) by the organizing thrombus formed around the catheter, which contains myofibroblasts. In busulfan-treated thrombocytopenic animals, there was no evidence for either neointimal development or thrombus formation. A direct role of this drug in the unresponsiveness of vascular wall can be excluded by the unchanged proliferation and migration pattern of cultured venous SMCs treated with busulfan compared to control cultures.

CONCLUSIONS

In our model, accumulation of differentiated SMCs in the neointima and myofibroblast appearance in the thrombus are linked, although distinct, events regulated by platelet activation, which is able to furnish the appropriate microenvironment for vascular SMC recruitment from the media/adventitial layer.

Effect of torsion on microvenous anastomotic patency in a rat model and early thrombolytic phenomenon

Torsion at the microanastomosis site is a basic fault and should be avoided. In this study, we investigate the effects of different degrees of microvenous torsion on patency and its physical changes on anastomoses in a rat model. One hundred anastomoses were performed at different degrees of torsion, using femoral veins of Sprague-Dawley rats. Anastomoses were performed at 0 degrees, 45 degrees, 90 degrees, 135 degrees, and 180 degrees of torsion randomly. Patency tests immediately, 1 h, and 1 week after the anastomoses were checked, using the refill test. Measurements of external diameter were recorded at three points: one at the anastomosis site, and the others 2 mm proximal and distal to the anastomotic site. Finally, histopathologic and scanning electron microscopy studies were performed. Subsequently, because of the peculiar phenomenon of early recannulation of the thrombosed vessels, 20 vessels were also explored on the first and the third days postoperatively. The data demonstrate that torsion at 180 degrees, compared with 0 degrees, 45 degrees, and 90 degrees, impaired patency significantly (P < 0.005). In the subsequent study of 20 veins that were thrombosed on the first day, all became patent on the third day and remained so. In conclusion, rotation of a microvenous anastomosis begins to affect the patency rate at 90 degrees of torsion, and at 180 degrees has a patency rate of only 25%. However, all become patent again from the third day onwards. Thrombosis of rat femoral veins without chronic obstruction results in rapid lysis of thrombus and transient proliferative changes.

Prognostic value of CT before thrombolytic therapy in iliofemoral deep venous thrombosis

PURPOSE

To prospectively assess the computed tomographic (CT) findings of iliofemoral deep venous thrombosis (DVT) and evaluate their relevance to the treatment of DVT with catheter-directed thrombolysis.

MATERIALS AND METHODS

Twenty-four consecutive patients with symptomatic iliofemoral DVT were studied with both nonenhanced and contrast-enhanced CT before thrombolytic therapy. Mean duration of clinical symptom was 15.8 days +/- 20.8 (range, 1-90 d). Selected CT findings were prospectively evaluated and correlated with duration of symptoms and outcome of thrombolytic therapy, including attenuation number of the thrombus on nonenhanced CT (in HU), presence of venous distention (distention ratio: vein diameter divided by the diameter of corresponding normal contralateral vein), and poor venous wall demarcation. The following threshold variables were also evaluated: attenuation > or =60 HU and distention ratio > or =1.5.

RESULTS

CT was suggestive of DVT in all patients, although different patterns were present. Higher attenuation on noncontrast CT was seen in patients who had favorable outcome of thrombolytic therapy compared to poor responders (66.1 +/- 8.7 vs 45.9 +/- 9.6; P <.0001). Distention ratio was also significantly higher in the good response group (2.6 +/- 1.4 vs 1.4 +/- 0.7; P <.05). Recent onset of clinical symptoms was associated with better outcome (9.4 d +/- 8.9 vs 28.6 d +/- 31.2; P <.03). Multiple-stepwise regression analysis of these variable produce the results of "attenuation >60" as the most predictive variable of favorable outcome of thrombolysis, followed by "distention ratio >1.5" and poor demarcation.

CONCLUSION

Selected CT findings are better predictors of a favorable outcome of thrombolytic therapy than duration of clinical symptoms alone.

Indications for surgical treatment of iliofemoral vein thrombosis

The goals of treatment of acute iliofemoral DVT should be prevention of fatal PE, reduction of pain and swelling of the involved leg, trying to stop the development of phlegmasia cerulea dolens and venous gangrene, prevention of disabling PTS by early removal of the blood clot, avoiding proximal venous obstruction, preserving normal, functioning valves in the leg veins, and preventing reflux. The authors recommend an aggressive approach with rapid removal of the occluding thrombus in the leg veins extending up into the iliac veins in active patients with a short history of symptomatic DVT, usually less than 7 days. This approach is not justified in chronically ill, bedridden, high-risk, or aged patients, or those with serious intercurrent disease or limited life expectancy. In these patients, such interventions can only be indicated for limb salvage in phlegmasia cerulea dolens when conservative treatment does not prevent the development of an acute compartment syndrome with venous gangrene. The preferred means of accomplishing early and quick removal of the thrombus is CDITT. Most of the authors' positive experience with thrombolysis is based on the use of urokinase. The Food and Drug Administration (FDA) has put this drug on temporary hold for almost 1 year. The alternative drugs (e.g., tissue plasminogen activator [tPA]) have not been tested for CDITT of DVT, and tPA is not FDA-approved for this indication. When there are contraindications or failure of thrombolysis, TE with a temporary AVF is a valid alternative.