New Model for in Vivo Quantification of Microvascular Embolization, Thrombus Formation, and Recanalization in Composite Flaps

Abstract

Background. Microthrombi are suggested to be involved in the pathogenesis of composite flap failure. Due to the lack of appropriate experimental models, however, the significance of microvascular thrombus formation and microthromboembolization in free flap failure remains poorly understood. The purpose of this study was therefore to develop a rat hindlimb model that allows tissue-confined in vivo analysis of thrombus formation, thromboembolization, and recanalization within the microcirculation of osteomyocutaneous flaps using intravital fluorescence microscopy. Materials and methods. Thrombus formation was induced photochemically in individual arterioles and venules of muscle, subcutis, and periosteum. To study thromboembolization, autologous arterial thrombi (40 μm) were preformed in vitro and were injected into the femoral artery supplying the osteomyocutaneous flap. Results. First platelet deposition was found independent from microvascular red blood cell velocity, while the subsequent growth of thrombus correlated inversely with red blood cell flow measured in the respective microvessel. Time required for complete thrombotic arteriolar occlusion exceeded 700 s, whereas thrombus growth in venules was found to be significantly accelerated (∼300 s) without differences between the individual tissues analyzed. The embolization resulted in a complete shutdown of capillary perfusion in muscle, subcutis, skin, and periosteum. During subsequent spontaneous recanalization, capillary perfusion increased in all tissues to approximately half of baseline, however, without further recovery during the 4-h postembolization period. Conclusion. The model presented is suitable to quantitatively study the pathophysiology of microvascular thrombus formation, thromboembolization, and recanalization in composite flaps, and may thus be used to evaluate the effectiveness of novel therapeutic strategies to prevent flap failure.