Visualizing The Pharmacological Delay Effect Of Botulinum Toxin A On The Flap Donor By The Infrared Thermography

Research background and purpose: 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.In this study,infrared thermography was used to observe the flap donor before BTX-A injection and after pharmacological delay,to explore the feasibility of visualizing the delayed effect of botulinum toxin type A by using infrared thermography,and to determine the transfer time.Methods: A total of 91 SD rats were randomly divided into 7 groups(13 rats in each group),including blank control group,BTX-A delay group(delayed by 2 weeks,3 weeks,and 4 weeks)and corresponding saline control group delayed by 2 weeks,3 weeks,and 4 weeks).The perforator flap(11×3cm)was designed on the unilateral dorsum of rats.In the BTX-A delay groups,a total of 15 IU of BTX-A was injected subcutaneously point by point after the observation with the infrared thermography.The saline control groups were given the same amount of saline.After the corresponding delay period,the flaps were observed again by the infrared thermography.After the observation,6 rats in each group conducted flaps elevation,4 rats underwent lead oxide arteriography,and 3 rats underwent CD31 immunohistochemical staining.The survival rate of the flaps was measured at the 7th day after surgery.Result: 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.The 2-week and 3-week BTX-A delay groups were statistically different from that of the control group in flap temperature and the number of transverse vessels in choke zone.Immunohistochemical staining showed that the microvascular density in the flap choke zone of the BTX-A delay groups was significantly higher than that of the normal saline control groups,and it continued to increase as the delay time increased.The microvascular density in the 4-week delay group was significantly higher than that in the 2-week delay group and the 3-week delay group.The survival rate of flaps in the BTXA delay groups were statistically different from that in the normal saline control group,but there was no difference between the groups.Conclusion: 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.