The Retrograde Limb of the Internal Mammary Vein in the Swine Model: A Sufficient Outflow Option in Free Tissue Transfer

Abstract

Sir: After reading the bright article entitled “The Retrograde Limb of the Internal Mammary Vein: An Additional Outflow Option in DIEP Flap Breast Reconstruction” by Kerr-Valentic et al.,1 we would like to present our unpublished experimental data with special regard to the outflow of the retrograde limb of the internal mammary vein. In a group of 8-week-old white swine (n = 12), the right internal mammary vessels were exposed and a microvascular clamp was applied to occlude the vein. The blood flow at the two ends of the internal mammary vein2 was depicted by the M-Turbo Ultrasound system (SonoSite, Inc., Bothell, Wash.), which is equipped with a high-frequency 12- to 20-MHz transducer. A normal venous Doppler signal with a continuous waveform was documented both proximally and distally. A latissimus dorsi myocutaneous flap was then transferred to the chest; the thoracodorsal artery was anastomosed to the anterograde internal mammary artery and the thoracodorsal vein to the retrograde internal mammary vein (Fig. 1). The idea for this experimental design arises from literature stating that the internal mammary vein lacks valves, thus allowing bidirectional blood flow.3 After 1 hour, flow through the flap was established and blood flow was depicted from the flap to the caudal limb of the internal mammary vein. Then, the flap was inset and secured with sutures over the sternum. No clinical evidence of venous congestion or arterial insufficiency was seen in any flap. After 48 hours, each animal was reanesthetized and anastomoses were exposed. Duplex ultrasonography depicted normal blood flow in all flaps; specifically, patent venous flow through the venous-to-venous anastomoses was documented (Fig. 2). Thus, the retrograde internal mammary vein is a sufficient outflow option in the swine model.Fig. 1.: The thoracodorsal artery (TDA) was anastomosed to the anterograde internal mammary artery (IMA) and the thoracodorsal vein (TDV) to the retrograde internal mammary vein (IMV).Fig. 2.: After 48 hours, duplex ultrasonography demonstrated retrograde venous flow away from the latissimus dorsi flap and into the retrograde internal mammary vein; the blue color depicts venous flow (away from the flap) in the retrograde vein.We would like to compliment the authors for their perception and method to give evidence that the retrograde limb of the internal mammary vein is an option as a recipient vein in humans. Nevertheless, to ensure success of the reconstruction, the authors anastomosed the one deep inferior epigastric perforator vena comitans to the antegrade and the other to the retrograde internal mammary vein. After the direction of flow in the caudal internal mammary vein was documented with duplex ultrasonography, the clamp on the antegrade vein was released.1 Thus, they documented venous outflow through the retrograde limb on only a short-term basis (15 minutes). However, our data suggested that the retrograde limb could support the outflow on a long-term basis as well, because it was used solely for the free flap drainage in our experimental model. The depiction of normal venous flow at the distal end of the internal mammary vein is essential in the decision to use it as an additional outflow. Loss of venous signal and/or the depiction of abnormal venous flow may indicate an occlusive or preocclusive pattern and thus may designate the distal limb as a nonreliable outflow option. In humans, especially irradiated patients or subjects with cardiovascular comorbidities, abnormal venous flow is often observed. Therefore, the intraoperative blood flow evaluation at both ends of the internal mammary vein is mandatory, before using the retrograde limb as an additional outflow in the scenarios that the authors described.1 Andreas Gravvanis, M.D., Ph.D. Dimosthenis Tsoutsos, M.D., Ph.D. Plastic Surgery Department General State Hospital of Athens “G. Gennimatas” Apostolos Papalois, Ph.D. Experimental Surgical Laboratory Andreas Karabinis, M.D., Ph.D. Intensive Care Unit Vasilios Dimitriou, M.D., Ph.D. Department of Anesthesiology Dimitrios Karakitsos, M.D., Ph.D. Intensive Care Unit General State Hospital of Athens “G. Gennimatas” Athens, Greece