Low-molecular-weight heparin (dalteparin) effectively prevents thrombosis in a rat model of deep arterial injury

Antithrombotic efficacy of direct oral anticoagulants on patency rate following microsurgical anastomosis in crushed rat arteries

BACKGROUND

During the last decade direct oral anticoagulants (DOAC) have been established in various fields of medicine.Their use in microsurgery has not been evaluated yet though. This study aims to evaluate their efficacy in microsurgery and additionally compare them with a well established antithrombotic agent.

MATERIALS AND METHODS

The right femoral artery of 101 rats divided into 4 groups, was crushed and anastomosed. Group A (20 rats) received placebo therapy (1 ml NaCl 0.9%, orally), while Group B (27 rats), Group C (27 rats) and Group D (27 rats) received rivaroxaban (3 mg/kg, orally), dabigatran (30 mg/kg, orally) and enoxaparin (30 mg/kg, subcutaneously) respectively. All drugs were administered 3 h preoperatively and once daily for the following postoperative days until the sacrifice of the animals. Patency was evaluated at 1st, 7th and 20th postoperative day. Following patency evaluation the rats were sacrificed and the vessels were harvested for histological examination.

RESULTS

None of the rats died postoperatively. Patency rates of rivaroxaban group (78%), dabigatran group (70%) and enoxaparin group (63%) were statistically similar, but significantly higher than the placebo-treated control group (p < 0.05). Cells with morphologic features of endothelial cells were evident 7 days after the injury.

CONCLUSION

The results of this study demonstrate the following: (1) rivaroxaban and dabigatran through inhibition of thrombus formation significantly enhanced the patency rate compared to placebo treatment (2) the antithrombotic efficacy of rivaroxaban and dabigatran in compromised microvessels was similar to that of enoxaparin, the most widely used antithrombotic agent.

Effect of Ethanol on Micro-Vessels Diameter and Prevention of Thrombosis

BACKGROUND

Microvascular surgery is one of the most important parts of reconstructive surgery. In the present study, the effect of ethanol on microvascular diameter and prevention of thrombosis was evaluated.

METHODS

Totally, 80 vessels including 40 arteries and 40 veins in right and left ears of 20 adult rabbits were enrolled. Seven days after injection of ethanol to rabbit ear vessel, vessel diameter and thrombosis rate post-iced saline challenge were documented and compared to normal saline injection in contralateral ear as a control group.

RESULTS

Vessel diameter in both arteries and veins in ethanol group was significantly larger than normal saline control group, and patency rates due to preventive effect of ethanol were also significantly higher in the ethanol group after iced saline challenge.

CONCLUSION

Pretreatment with ethanol can enlarge vessel diameter and play a preventive role on thrombosis after iced saline challenge.

Thromboprophylaxis in Head and Neck Microvascular Reconstruction

Head and neck patients undergoing microvascular reconstruction are at high risk for thromboembolism. While the prevention of thromboembolism has become an essential aspect of care, within the field of microsurgery, concern for anastomotic complications have hindered the creation of an accepted regimen. The aim of this review was to evaluate the risks and benefits of prophylactic agents for thromboprophylaxis. A literature search was conducted in MEDLINE, Cochrane Library, and PubMed/NCBI databases. Articles discussing thromboprophylaxis in otolaryngology, head and neck surgery, or microvascular reconstruction were considered in the review from the past 30 years. The majority of patients undergoing microvascular surgery have multiple risk factors for thrombus formation. Several consensus guidelines exist for the prophylaxis in patients who are critically ill, undergoing surgery, or with malignancy. Significant evidence supports the routine use of mechanical means, such as early mobilization and pneumatic compression along with subcutaneous heparin. Low-molecular-weight heparin is also frequently utilized, although results are largely divided. Data on aspirin remain equivocal. Studies on microvascular failure and flap loss have demonstrated little to no association with chemoprophylaxis. The evidence for postoperative thromboprophylaxis regimens in patients undergoing head and neck free tissue transfer is variable. Multiple studies have supported the use of unfractionated heparin or low-molecular-weight heparin. There appears to be an expert consensus for the combined use of mechanical prophylactic methods and chemical prophylaxis. Prospective randomized trials are required to validate the most effective combination of chemoprophylaxis agents.

Management of the Pediatric Patient Following Upper Extremity Replantation or Revascularization: A Suggested Protocol

BACKGROUND

Traumatic pediatric amputations of the hand and upper extremity can have long-term financial, psychological, developmental, and functional consequences that readily extend beyond the realm of that which is normally encountered in comparatively injured adults. These factors, along with a paucity of medical comorbidities, have guided a more liberal and aggressive approach to treating pediatric amputations in hopes of optimizing psychosocial, aesthetic, and developmental outcomes. Furthermore, advances in pharmacology and microsurgical replantation techniques have allowed what were otherwise exceedingly rare surgeries to become commonplace in hospitals all over the world. Despite these gains, vascular thrombosis remains the leading cause of failure in microvascular surgeries. A recent survey showed that 96% of reconstructive surgeons use some form of anticoagulation therapy in their treatment, but no consensus regarding pharmacologic agents, dosing, or efficacy exists. The risk of thrombosis is further complicated by the dynamic nature of vasculature in response to stressors such as sympathetic tone, decreased intravascular volume, and response to external temperature. Given the lack of a higher-level evidence to guide the replantation surgeon in postoperative orders, we created an inclusive protocol, outlining complete and proper management of the pediatric patient following revascularization or replantation surgery.

METHODS

We reviewed the methods employed by our microvascular surgeons and consulted with board-certified pediatricians to produce a final document that was adopted ubiquitously among our providers.

RESULTS

We do not have head-to-head data demonstrating improved outcomes with use of the protocol. Nonetheless, the original document has been modified and reproduced here for your consideration and use.

CONCLUSIONS

Since initiating the protocol, we feel it has helped standardize our practice, avoid instances of incomplete or missed order sets, and facilitate interdisciplinary management through decreased gaps in communication, especially in those surgeries terminating in the middle of the night.

Experimental Thromboprophylaxis with Low Molecular Weight Heparin After Microsurgical Revascularization

There is great variability among microsurgeons as regards the use of prophylactic anticoagulant after revascularization and this is probably due to lack of comparative data. Also, there has been much debate regarding the benefit of anti-thrombotic therapies versus the risk of complications such as systemic bleeding and hematoma formation. To evaluate the effectiveness of postoperative low molecular weight heparin (LMWH) as a prophylactic anticoagulant therapy after microsurgical repair of the femoral artery and vein in rats. Randomized, blinded study. The femoral artery and vein of 40 Sprague Dawley rats were sectioned and repaired with microsurgical sutures under general anesthesia. They were randomly divided into 2 groups: Group (A) in which the 20 rats were injected with Enoxaparin subcutaneously at a dose 1.5 mg/kg once daily for 3 successive days; Group (B), the control group, in which 20 rats were injected with isotonic sodium chloride 0.9 % subcutaneously in a blinded fashion. After 7 days, the femoral vessels were re-explored and patency of the femoral vessels was assessed with empty-and-refill test. There were a total of 12 vascular thrombosis among 74 microsurgical repair in both groups with percentage of 16.22 % including, 5 arterial anastomosis and 7 venous anastomosis. The incidence of thrombosis in the treatment group (A) was 18.4 % while the incidence of thrombosis in the control group (B) was 13.8 %. This difference was not statistically significant using Fisher exact test. Postoperative administration of LMWH did not provide the desired protection against thrombosis after microsurgical vascular repair.

A modified vascularized whole knee joint allotransplantation model in the rat

Previous papers have shown surgical neoangiogenesis to allow long-term bone allotransplant survival without immunosuppression. Whole joint composite tissue allotransplants (CTA) might be treated similarly. A novel rat knee CTA model is described for further study of the roles of neoangiogensis in joint allotransplant survival and adjustment of immunosuppression. Microvascular knee CTA was performed in nine rats across a major histocompatibility barrier with both pedicle repair and implantation of host-derived arteriovenous ("a/v") bundles. In the control group (N = 3), the pedicle was ligated. Immunosuppression was given daily. Joint mobility, weight-bearing, pedicle patency, bone blood flow, and sprouting from a/v bundles were assessed at 3 weeks. All but the nonrevascularized control knees had full passive motion and full weight bearing. One nutrient pedicle thrombosed prematurely. Blood flow was measurable in transplants with patent nutrient pedicles. Implanted a/v bundles produced new vascular networks on angiography. This new rat microsurgical model permits further study of joint allotransplantation. Patency of both pedicles and implanted a/v bundles was maintained, laying a foundation for future studies.

Human activated protein C variants in a rat model of arterial thrombosis

BACKGROUND

Activated protein C (APC) inhibits coagulation by degrading activated factor V (FVa) and factor VIII (FVIIIa), protein S (PS) functioning as a cofactor to APC.

METHODS

By mutagenesis of the vitamin K-dependent Gla domain of APC, we have recently created an APC variant having enhanced anticoagulant activity due to increased affinity for negatively charged phospholipid membranes. In the present study, the potential antithrombotic effects of this APC variant, and of a variant APC that is additionally mutated in the serine protease domain, have been evaluated in a blind randomized study in a rat model of arterial thrombosis. In this model, we have previously found the combination of bovine APC and PS to be highly antithrombotic. Four treatment groups each containing 10 rats were, in a blind random fashion, given intravenous bolus injections of wild-type or mutant variants of APC (0.8 mg/kg) together with human PS (0.6 mg/kg) or human PS (0.6 mg/kg) alone. A control group with 20 animals where given vehicle only.

RESULTS

A trend to increased patency rates was noted in a group receiving one of the APC variants, but it did not reach statistical significance.

CONCLUSION

In conclusion, administration of human APC variants having enhanced anticoagulant efficacy together with human PS in a rat model of arterial thrombosis did not give an efficient antithrombotic effect. The lack of effect may be due to species-specific differences between the human protein C system and the rat hemostatic system.

Various Local Hemostatic Agents with Different Modes of Action; an in vivo Comparative Randomized Vascular Surgical Experimental Study

OBJECTIVES

To evaluate the effects of different local hemostatic agents in a new high flow vascular experimental bleeding model.

DESIGN

Bovine thrombin combined with collagen matrix (bTcM), microporous polysaccharide hemospheres (MPH), freeze-dried rFVIIa with and without the combination of MPH were compared to a control group (solely compression) in a randomized fashion (20 animals/group). Primary endpoint was hemostasis, and secondary endpoints were time to hemostasis, blood loss, and blood pressure at hemostasis.

METHODS

The common carotid artery of heparinized rats was ligated proximally and transected. Compression was applied for one minute followed by application of the topical hemostatic agent. Compression was maintained for another two minutes followed by re-evaluation of hemostasis: if bleeding continued additional compression was applied and thereafter bleeding was checked every minute until hemostasis.

RESULTS

All animals in the bTcM group obtained hemostasis compared to 20% in the control group (p<0.0001). The combination of MPH and rFVIIa (70% hemostasis) also showed a significant hemostatic capacity compared to control group (p<0.001). None of the other active treatment groups differed compared to control group. Animals treated with bTcM had a significantly shorter time to hemostasis compared to animals in the other active treatment groups. No significant difference in blood loss and blood pressure at hemostasis was detected.

CONCLUSIONS

The most effective hemostatic agent was bTcM, followed by the combination of rFVIIa and MPH, while neither MPH nor rFVIIa alone displayed any hemostatic capacity compared to compression only.

Comparative study of isovolemic hemodilution with 3% albumin, dextran-40, and prophylactic enoxaparin (LMWH) on thrombus formation at venous microanastomosis in rats

The objective of the present investigation was to compare the effect of isovolemic hemodilution with 3% albumin, dextran-40, and enoxaparin on the prevention of thrombosis in femoral vein microanastomosis using an experimental model in rats. Forty male Wistar rats were allocated into four groups: group 1, control, thrombogenic model without previous treatment; group 2, hemodiluted, thrombogenic model with previous hemodilution; group 3, dextran-40, thrombogenic model with dextran infusion (10 ml/kg), and group 4, enoxaparin, thrombogenic model with administration of enoxaparin (0.5 mg/kg/day). Hemostatic parameters, hematologic examinations, patency of anastomosis, and histopathological examination were evaluated. The hemostatic parameters were similar in the four groups studied. Group hemodiluted, dextran-40, and enoxaparin showed significantly reduced number of red blood cells and platelets as compared with the control group. The hemodilution significantly increased the patency rates of the vein at 20 min and 48 h. Dextran-40 and enoxaparin improved the patency of the vein only at 20 min, but failed to show a significant increase in the final patency at 48 h. After 48 h, the rate of venous thrombosis, as evaluated microscopically, was significantly decreased in hemodiluted animals (1/8) as compared with controls (10/10); in rats treated with dextran-40 (7/10) and enoxaparin (5/10) the rate of venous thrombosis was significantly higher as compared with rats of the group hemodiluted. Based on these observations, it can be concluded that hemodilution with albumin 3% was a safe and more adequate procedure than the use of the schemes of administration of dextran-40 and enoxaparin used in this study to prevent thrombus formation at femoral vein microanastomosis in rats. Since hemodilution promotes reduction in blood viscosity and in erythrocyte and platelet aggregation as well as dilution of the coagulation factors themselves, its use could provide better microcirculatory blood perfusion, decreasing the risk of thrombosis, and making possible safer microsurgical procedures.

The antithrombotic and anti-inflammatory effects of BCX-3607, a small molecule tissue factor/factor VIIa inhibitor

Tissue factor (TF) is a transmembrane glycoprotein that binds its zymogen cofactor, Factor VIIa (FVIIa) on the cell surface. Together (TF/FVIIa) they activate Factor X (FX) and Factor IX (FIX) and start the extrinsic pathway of blood coagulation. As such, the TF/FVIIa complex plays an important role in normal physiology as well as in thrombotic diseases such as unstable angina (UA), disseminated intravascular coagulation (DIC), and deep vein thrombosis (DVT). In addition to its function as an initiator of coagulation, TF/FVIIa plays an important role in inflammation. Expression of TF on the cell surface and its appearance as a soluble molecule are characteristic features of acute and chronic inflammation in conditions such as sepsis and atherosclerosis. Here we demonstrate that BCX-3607, a small molecule potent inhibitor of TF/FVIIa, reduces thrombus weight in an animal model of DVT. BCX-3607 also decreases the level of interleukin-6 (IL-6) in a LPS-stimulated mouse model of endotoxemia. Additionally, in vitro studies indicate that BCX-3607 blocks the generation of TF/FVIIa-induced IL-8 mRNA in human keratinocytes and reduces the TF/FVIIa-mediated generation of IL-6 and IL-8 in human umbilical vein endothelial cells (HUVEC). Therefore, BCX-3607 might block the TF/FVIIa-mediated coagulation and inflammation associated with pathological conditions.

Anticoagulation therapy in microsurgery: a review

The advent of microsurgical tissue transfer including replantation greatly has expanded the scope of reconstructive surgery. There are few recent innovations in anticoagulation therapies for microsurgery, however, and anastomotic thrombosis remains an occasional cause of surgical failure. No consensus exists on the ideal anticoagulation protocol for microsurgery. This article reviews major pharmacologic modalities of anticoagulation, delineates the mechanism of action and study of efficacy of each agent, and compares the risks and benefits of popular anticoagulation therapies. Finally, it examines available human outcomes-based data and attempts to provide a glimpse of the future direction of microsurgical anticoagulation research.

Effect of low molecular weight heparin on fracture healing in a stabilized rat femur fracture model

The purpose of this study was to evaluate the effect of low molecular weight heparin (LMWH) on fracture healing in a standard stabilized rat femur fracture model. A closed, mid-diaphyseal transverse fracture was created in the right femur of Long-Evans rats after insertion of a 0.8-mm K-wire into the medullary canal. Animals were randomized to receive either LMWH (70 units/kg dalteparin) or an injection of normal saline daily for 2 weeks. Animals were sacrificed at 2, 3, and 6 weeks. Fracture healing was assessed by radiographs, histology, and mechanical testing. There were no significant differences between the control and LMWH groups in the percentage of animals with radiographic bridging callus at each time point. Histologic appearance of fracture healing was similar between the control and LMWH groups. There were no significant differences in the normalized mechanical properties of the control and LMWH groups at 2 and 3 weeks. At 6 weeks, the percent torque of the LMWH group was significantly greater than the control group ( p = 0.0072), however, there was no significant difference in the stiffness and energy absorption. Dalteparin, at the dosage used in this study, did not impair fracture healing in this standard stabilized rat femur fracture model.

The Effect of Fondaparinux Versus Enoxaparin in the Survival of a Congested Skin Flap in a Rabbit Model

BACKGROUND

The purpose of this study was to evaluate the effects of fondaparinux, a selective antithrombin III agonist, in comparison to the low-molecular-weight heparin enoxaparin in the survival of a congested skin flap.

MATERIALS AND METHODS

Eighteen axial-pattern auricular flaps were performed on rabbits using a well-described congested flap model. Animals were randomized into 2 treatment groups, enoxaparin (n = 6) and fondaparinux (n = 6), and a control group (n = 6) that received no treatment. Skin flap survival area was measured postoperatively at 7 and 14 days.

RESULTS

The groups that received fondaparinux and enoxaparin had similar mean flap survival areas and were not statistically different. However, both treatment groups significantly increased flap survival compared with controls (P < 0.014).

CONCLUSIONS

Fondaparinux, like enoxaparin, significantly improves survival of congested flaps in rabbits. Its use instead of enoxaparin may be warranted, given that it eliminates the risk of heparin-induced thrombocytopenia. Further study in humans is warranted.

[Low molecular weight heparin in patients undergoing vascular surgery]

OBJECTIVES

Despite the fact that there are no approved indications by the French regulatory agency and despite the absence of recommendations, low molecular weight heparins (LMWH) are frequently used in vascular surgery, an area at both high risk of perioperative arterial and venous thrombosis as well as of bleeding. The aim of this study was to investigate medical practice in vascular surgery, using a survey of prescribers of antithrombotic agents.

STUDY DESIGN

Survey of physicians from different specialities involved in patient care before, during, and after vascular surgery.

PATIENTS AND METHODS

Between March and June 2003, 301 physicians filled a questionnaire providing information about their antithrombotic regimens depending on the type of vascular surgery. These physicians are involved in an important part of vascular surgery activity in France.

RESULTS

The survey confirmed the use of LMWH in near 80% of patients scheduled for vascular surgery. The prescribed LMWH is frequently associated with antiplatelets agents. During patient's hospitalization, LMWH prescription is guided by numerous factors, making the prescription protocol rather complex. Major risk factors favoring continued prophylaxis after patient's hospital discharge include surgery with a high risk of thromboembolic events and limited ambulation. Analysis of the data also showed that the surgeon and the referring physician are both implicated in the majority of the postoperative care following patient's discharge, and therefore, in prescribing the antithrombotic drug.

CONCLUSION

This survey gives information on practical use of LMWH in the vascular surgery setting. This information could lead to prospective studies of LMWH in situations other than venous thromboembolic disease.

Can low molecular weight heparin replace unfractionated heparin during peripheral arterial reconstruction? An open label prospective randomized controlled trial

OBJECTIVE

This study was undertaken to evaluate the effect of low molecular weight heparin (LMWH) compared with unfractionated heparin (UFH) on the rate of occlusion and bleeding during peripheral vascular surgery.

METHODS

The study was an open label, prospective, randomized trial, carried out by 20 Swedish surgical and vascular surgical departments that report to the Swedish Vascular Registry (SWEDVASC). Study subjects included patients undergoing peripheral vascular procedures, except carotid surgery. Of the 849 patients included, 817 were followed up to 30 days. LMWH (40 mg of enoxaparin) or UFH (5000 IU heparin) was given intravenously immediately before clamping. The same formulation in diluted form was used for vascular rinsing. Main outcome measures included patent reconstruction at day 1, perioperative blood loss, and the percentage of patients requiring protamin. Further, 30-day data for mortality, repeat operation, and recurrent occlusion are reported.

RESULTS

The mortality rate at 30 days was 2.7%, with no difference between groups. The patency rate at 1 day was 91.2% to 98.4%, depending on diagnosis and type of reconstruction. No difference was recorded between study groups (0.6 < P < 1.0). At 30 days the patency rate was 83.1% to 100% (0.2 < P <.9). Median blood loss was 350 mL (interquartile range [IQR], 200-800 mL) in the LMWH group and 425 mL (IQR, 200-900 mL) in the UFH group (P =.02). Protamin was given to significantly fewer patients in the LMWH group (P =.001). LMWH was comparable to UFH during peripheral vascular reconstruction in terms of 1-day and 30-day graft patency, operative blood loss, and hemorrhagic complications. Protamine was required less often after LMWH. In this randomized trial LMWH was as effective as UFH in preventing thrombosis without excess bleeding or hemorrhagic complications.