Visualizing the pharmacological preconditioning effect of botulinum toxin A by the infrared thermography in a rat pedicled perforator island flap model.

BACKGROUND Surgical delay can improve flap viability, leading to vasodilation, neovascularization, and vessel reorganization. Experiments suggest similar positive effect of botulinum toxin A (BTX-A) on pedicled flaps' viability. However, whether it may convert the choke anastomoses into the true anastomoses and how to identify the optimal timing for flap transfer remains unclear. METHODS One hundred and fifty-four Sprague-Dawley rats were divided into a control group, three saline injection groups, and three BTX-A injection groups defined by time of injection (2, 3, 4 weeks before flap harvest). A pedicled flap of 11×3 cm was marked on the unilateral dorsum of rat. Before flap harvest, the flap donors were assessed by the infrared thermal imaging, postmortem arteriography, immunohistochemical staining of CD 31 and ELISA. Flap survival areas percentage was measured on postoperative day 7. RESULTS In the control group and saline groups, the infrared thermography showed three independent white hotspots interspaced by red zones over flaps, whereas it presented a continuous white band in the BTX-A groups. There was a significant increase in the flap survival area, flap surface temperatures, the numbers of identifiable vessels in the choke zones, microvascular density and vascular endothelial growth factor concentration in the BTX-A groups. CONCLUSIONS BTX-A can convert the choke anastomoses into the true anastomoses and its preconditioning effect cannot increase over time; it is appropriate to choose the timing point when the infrared thermal images show a continuous white band existing over flaps for flap transfer.