Laser-induced primary and secondary hemostasis dynamics and mechanisms in relation to selective photothermolysis of port wine stains

Background: Superficial vascular anomalies such as port wine stains are commonly treated by selective photothermolysis (SP). The endovascular laser-tissue interactions underlying SP are governed by a photothermal response (thermocoagulation of blood) and a hemodynamic response (thrombosis). Currently it is not known whether the hemodynamic response encompasses both primary and secondary hemostasis, which platelet receptors are involved, and what the SP-induced thrombosis kinetics are in low-flow venules. Objectives: To (1) define the role and kinetics of primary and secondary hemostasis in laser-induced thrombus formation and (2) determine which key platelet surface receptors are involved in the hemodynamic response. Methods: 532-nm laser-irradiated hamster dorsal skin fold venules were studied by intravital fluorescence microscopy following fluorescent labeling of platelets with 5(6)-carboxyfluorescein. Heparin and fluorescently labeled anti-glycoprotein Ib-α (GPIbα) and anti-P-selectin antibodies were administered to investigate the role of coagulation and platelet receptors, respectively. Lesional sizes were quantified by software. Results: Laser irradiation consistently produced sub-occlusive thermal coagula. Thrombosis was triggered in all irradiated venules in a thermal coagulum-independent manner and peaked at 6.25. min post-irradiation. Heparin decreased the maximum thrombus size and caused thrombosis to reach a maximum at 1.25. min. Immunoblocking of GPIbα abated the extent of thrombosis, whereas immunoblocking of P-selectin had no effect. Conclusions: The hemodynamic response ensues the photothermal response in a thermal coagulum-independent manner and involves primary and secondary hemostasis. Primary hemostasis is mediated by constitutively expressed GPIbα but not by activation-dependent P-selectin.