The Shunt-Restricted Arterialized Venous Flap
An arterialized venous flap is a cutaneous flap based on subcutaneous veins (most often using veins in the forearm) with no actual identifiable artery. The skin and subcutaneous tissue are harvested while preserving their connections to the superficial venous system. To provide blood flow to the flap, one end of the vein is anastomosed to a recipient artery (thus “arterialized”), while the other end of the vein is anastomosed to a recipient vein. The flap is perfused by nonphysiologic flow of blood from the vein into the peripheral tissue. Therefore, the size of the flap is limited.
Although the concept had been introduced more than three decades ago, it remains unpopular because of the tendency of this flap to develop significant venous congestion postoperatively. This problem is to be expected, especially when a venous flap is designed in an antegrade flow-through fashion, with the same vein (or a branch of the same vein) providing inflow (afferent) and outflow (efferent) for the flap. This creates an unrestricted arteriovenous (AV) shunt, where the arterial blood may bypass the peripheral tissue without egress into the capillary beds. Moreover, the efferent end of the vein experiences nearly the same (arterial) pressure as the afferent end, which impedes the return of venous blood from the flap.
Several strategies have been proposed to overcome this problem, such as repairing multiple efferent veins, employing a smaller afferent vein and a larger efferent vein, performing various chemical or mechanical delay procedures, and transferring the flap in a retrograde fashion to utilize the resistance of the valves to lower the pressure in the efferent vein. While high rates of “success” have been reported with these modifications, venous congestion remains troublesome and often results in partial flap loss.1 Since the goal is to achieve functional soft-tissue coverage of a digit, even a small amount of fibrosis from secondary healing can result in failure.
Our design uses an antegrade flap, with the main concept to utilize different veins for arterialization and venous drainage, thereby “individualizing” the veins into an afferent portion that is under arterial pressure and an efferent portion that has minimal intraluminal pressure. By doing so, AV shunting is “restricted,” or minimized. Venous drainage from the flap is facilitated by the low intraluminal pressure in the efferent vein, and venous congestion is minimized. AV shunt restriction can be accomplished in several ways, depending upon the venous pattern within the flap.2
Indications
Defects on the hand/digit that cannot be resurfaced by a local or a regional flap
Composite tissue defects requiring replacement of both tendon and soft tissue (e.g., harvesting palmaris longus along with the venous flap in volar forearm)
Contraindications
There is no absolute contraindication for a shunt-restricted arterialized venous flap transfer.
A venous flap based on deep-seated superficial veins or with thick subcutaneous fat may not be a good choice as it prevents visualization of the venous system and makes shunt restriction difficult.
When revascularization of the distal part of the digit is also required, a flow-through venous flap is indicated instead of the shunt-restricted arterialized venous flap.
We recommend caution when using our technique for very large flaps, since adequate control of direct AV shunting would be more difficult when an abundant venous network exists within a broader territory. In these instances there is an assortment of thin perforator flaps that can be used.
Examination/Imaging
No special examination or imaging study is required prior to harvesting a venous flap from the distal volar forearm. The only prerequisite is that the veins must be located superficial enough to be visualized when a tourniquet is applied. During the preoperative physical examination, if a patient has deeply seated veins or thick subcutaneous fat that prevents visualization of the superficial venous system, alternatives to a venous flap should be considered.
Relevant Anatomy
The specific method to restrict AV shunting is dependent on the venous pattern, as described below and illustrated in Fig. 54.1 . (Note that all flaps are designed for antegrade flow; thus, the afferent end of the flap is located more distally on the forearm.)
II-pattern: two parallel and separate veins without any visible interconnection. In this situation, AV shunting can be avoided simply by using one vein for inflow and the other for outflow. The afferent vein is arterialized (pressurized), thus forcing arterial blood into the peripheral tissue; but, because of the absence of an interconnection between the two veins, the efferent vein maintains a physiologic venous pressure and permits drainage of venous blood from the flap.
H-pattern: two parallel veins with transverse interconnecting branch(es). The interconnecting branches are ligated, and separate veins are used for inflow and outflow (as with II-pattern flaps).
Y-pattern: one vein entering the afferent end of the flap, bifurcating into two branches that exit the efferent end. One of the efferent branches is ligated at the end, thus forming an inflow-only segment when arterialized. The other efferent branch is ligated downstream to the venous bifurcation, thereby becoming isolated from the afferent branch and serving as an outflow-only segment. Ideally, the Y-pattern flap should be designed with the bifurcation located as close to the afferent end (the more distal portion of the forearm) as possible. This maximizes the length of the outflow vessel within the flap.
λ (lambda)-pattern (reversed Y-pattern): two veins entering the afferent end of the flap, merging to form a single vein that exits the efferent end. This is the opposite of the Y-pattern, and the strategy is reversed, with ligation of one of the afferent branches upstream from the merging point. The afferent branch that has been ligated upstream from the merging point will act as the inflow segment. The other afferent branch is ligated at its afferent end, acting solely as an outflow segment. In designing a λ-pattern flap, the bifurcation should be located as close to the efferent end (the more proximal portion of the forearm) as possible to maximize the length of the inflow vessel within the flap.
I-pattern: one continuous vein running along the length of the flap. Because the single vein must provide both inflow and outflow, the vessel is ligated at its midpoint so that only the afferent half is arterialized. The length of the vein traveling within the flap should be maximized to optimize both the perfusion and venous drainage of the flap.
Pitfalls
Arterialized venous flaps have a low resistance to infection. They are not suitable for providing coverage for chronic, ulcerative defects.
This technique may not be reliable in flaps with larger dimensions (maximum flap dimension was 3.5 × 7.5 cm2 in our series).
Complications
Mild-to-moderate venous congestion
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