Reply: The reliability of evaluating flap survival with Infrared Thermography and the mechanism of improving flap survival by Botulinum Toxin Type A

Sir: We would like to thank Xiaomu Ma et al. for their comments on our article entitled “Visualizing the Pharmacologic Preconditioning Effect of Botulinum Toxin Type A by Infrared Thermography in a Rat Pedicled Perforator Island Flap Model.”1 In this study, we evaluated the beneficial effect of preconditioning by botulinum toxin type A on the flap survival in a pedicled perforator island flap rat model. We concluded that (1) the pretreatment with botulinum toxin type A can effectively improve flap survival by converting choke anastomoses to true anastomoses; (2) this conversion can be identified by infrared thermography on the flap donors after pretreatment, which shows a characteristic continuous white band; and (3) the optimal timing for flap transfer can be determined by infrared thermography.1 Xiaomu Ma et al. considered that the occurrence of a continuous white band visualized by infrared thermograms on the flap donors after botulinum toxin type A may indicate an increase in blood flow of the arterial perforators instead of the conversion of linking patterns; in addition, they proposed that the effect of botulinum toxin type A preconditioning may come from botulinum toxin type A–induced vasodilation of arterial perforators and subsequent increase in blood flow rather than the conversion of linking patterns. First, we need to say that the conversion of linking patterns induced by botulinum toxin type A was demonstrated by an increase in the number of transverse vessels rather than vasodilation in the choke zones on postmortem arteriography. This conversion of linking patterns is characterized by a significant increase in the number of transverse vessels in the choke zones on postmortem arteriography.2,3 Second, the perforator angiosomes on infrared thermography show white, whereas the choke zones manifest red areas in Sprague-Dawley rats.3 Infrared thermography displays a temperature difference as a color-coded image, with red indicating low temperature and white indicating high; only when choke anastomoses are converted into true anastomoses, the choke zones present white.3 Third, the number of perforator angiosomes captured by a cutaneous perforator does not increase unless the choke anastomoses are converted into true anastomoses.4 Based on the preliminary results, we consider that pretreatment with botulinum toxin type A improves the survival of pedicled perforator island flaps by converting choke anastomoses to true anastomoses rather than by vasodilation of the arterial perforators. How the choke anastomoses convert to true anastomoses by botulinum toxin type A remains unclear; we suppose that botulinum toxin type A may paralyze vascular smooth muscle cells of the choke vessels by inhibiting the release of acetylcholine from the presynaptic membrane, resulting in the conversion of choke anastomoses to true anastomoses. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication.