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Synthetic grafts are being widely used to bypass occluded vessels or to supply blood flow. Thrombosis of these grafts is a major complication. The clots are often formed during the first exposure of blood to the graft surface which later become a nidus for larger clots. We examined whether pretreatment of the graft with heparin prevents this initial clotting process.
A circuit was assembled to compare two sets of shunts in the same subject. This circuit simulated a systemic-pulmonary shunt with inflow cannula in the aorta, branching to 2 groups of study and control grafts, connected to an outflow cannula in the pulmonary artery. The study group was treated with heparin for 15 minutes prior to placement in the circuit. With installation of the circuit, the blood flowed from the aorta to a set of multiple branches all the same size and properties with the only difference being exposure to heparin.
Pressure was monitored proximal and distal to the branches to verify similar flow dynamics in each group. After 2 hours of simultaneous and equal flow in all branches the circulation was discontinued and the grafts were irrigated and sliced open to expose the inner surface. Digital images were taken in a standard technique coded for each graft for a blinded analysis. The images were analyzed by image analysis software. The density and area of the pixels was proportionate to the amount of the clot formed on the graft surface.
The pressure gradient between the groups was identical throughout the study, meaning similar flow characteristics were maintained in all branches. The pretreated grafts had fewer blood clots adhered to the surface by direct visual inspection. The image analysis showed 5 vs.39 clots, 0.01% vs. 1.8% clotted area and 62 vs. 5630 clot pixel area between the treated and non-treated grafts respectively, p <0.05.
Pretreatment of the synthetic graft with heparin prior to implantation reduces the risk of early clot formation. This simple practice might be helpful to prevent initial thrombosis of the graft and later occlusion especially in critical situations where the patency of the graft is crucial.
- 2013 American College of Cardiology Foundation