Arterial and Venous Stasis

Cardiovascular diseases associated with intravascular thrombosis are among the most common causes of death in both developed and developing countries. Arterial thrombosis leads to myocardial infarction while venous thrombosis is a frequent side-effect of oncology drugs.

The stasis-induced thrombosis model (aka the Wessler Model) is a classical method to evaluate potential effective antithrombotic agents. It combines local arterial or venous stasis with hypercoagulability produced by the injection of thromboplastin into the systemic circulation of rabbits or rats.

IPST currently runs several thrombosis and homeostasis models including the Wessler (venous stasis) model, which involves the occlusion of a segment of the rabbit jugular vein. Our venous stasis models include vessel clamp (stasis), with or without clotting agent, followed by reperfusion, thrombus examination, etc. Bleeding time is also measured from a standard incision made on the ventral part of the rabbit’s ear.

The potential antithrombotic agent is administered and the carotid artery or jugular vein (vena cava in rats) is occluded by clamp one (1) minute after the injection of the hypercoagulant into the circulation.

Over the years, IPST has used several coagulation factors as reference compounds to induce thrombosis, such as NovoSeven and human FXIa. Our experience with the model includes various endpoints aimed at evaluating thromboembolitic propensity in the rabbit venous stasis model.

Synthetic molecules, naturally occurring peptides, IVIGs, have all been tested here. IVIGs also require precautious infusion to reduce thromboembolic events – and as such, we have had to develop special protocols for those.

Other assays such as aPTT/PT, platelets aggregation and TEG5000 are also available if they can support or refine the findings of a study.

TEG-FaceRightIPST has recently completed the validation of a TEG5000 thromboelastograph for IVIG bath quality control. The test is added to the standard Wessler assay produced for IVIG batch clearance, and the North American regulators, in the United States and Canada, have been very pleased with the refinement it brings to the assay.

Thromboelastography (TEG) is yet another method of assessing the coagulation cascade in blood. While preclinical methods often rely on optical platelet aggregation assays using platelet-rich plasma, clinical procedures work directly with whole blood from a patient. This allows less fluid handling, supposedly more rapid results which can be useful immediately in the context of surgical procedures, or belatedly during diagnostics.

TEG relies on the “thickening” of whole blood once the coagulation cascade is activated; a paddled-shaft measures the resistance of the blood to motor-driven torsion, giving a direct readout of the consistence of the coagulated blood. The method uses 250 µL of whole blood, and is a perfect complement to whole-animal Wessler assays, in which in-situ coagulation/thrombus formation is measured after a short stasis period. Combined with bleeding time  and optical (Chronolog) platelet aggregation assessments, also on the same Wessler animal, one gets a very thorough examination of coagulation, thrombogenicity, and platelet aggregation.

All in all, it’s probably a good idea – and definitely economically viable – to work TEG into your testing strategy.

End points:

  • Blood sample analysis: CBC
  • Thrombus weight
  • Thrombus score
  • Bleeding time

Rabbit, Rat