Effects of venous supercharging in deep inferior epigastric artery perforator fl ap

Purpose: To evaluate the effects of venous supercharging in deep inferior epigastric artery perforator fl ap in rats. Methods: 20 Wistar rats were randomized in 2 groups: control group (C), all had fl aps raised based on the deep inferior epigastric perforator vessels (DIEP), and experimental group (E), which was identical to group C, except that the contralateral superfi cial inferior epigastric vein was also kept with the fl ap. Flow studies using laser Doppler fl owmetry where performed daily in the four zones of the fl ap. On the 7th postoperative day rats were killed and fl ap survival was determined using digital planimetry. Results: Flow values were presented as a percentage of the baseline fl ow after incision of the fl ap edges. The surviving fl ap area was demonstrated as a percentage of the total fl ap area. Evaluation by digital planimetry showed that fl ap survival in group E was higher than in group C (97,38%±1,32%vs.44,13%±4,83%, p=0,0006). Conclusion: This study shows that venous supercharging of the rat DIEP fl ap results in greater fl ap survival.


Introduction
Random fl aps were used in the past as the sole resource for defects coverage; however those fl aps had limited applications regarding location and size of the defect.These limitations were solved by incorporating a vessel within the fl ap, the axial fl ap.Mathes and Nahai in early 80's described the muscles irrigation pattern, and muscles started to be used as fl aps.The great advantage of muscle fl aps is the rich arterial supply, which makes it a great choice for bigger defects.Later Koshima and Soeda 1 introduced a new concept: a fl ap presenting the same advantages of muscles fl aps, however without the morbidity related to the donor area.This concept originated the perforator fl aps.The fi rst perforator fl ap was described by Koshima and Soeda 1 , composed of periumbilical fat and skin, with total preservation of rectus abdominus muscle.After the fi rst description, these fl aps were described for various purposes: lower and upper limb reconstruction, head and neck reconstruction and even augmentation mammoplasty.Allen and Treece 2 described their experience with these fl aps in breast reconstruction.Promising results in this fi eld had turned perforator fl aps in a very important option in breast reconstruction 3 , especially because several series showed lower donor site morbidity.Some partial fl ap loss were described, and it was hypothesized the those fl aps were more susceptible to venous congestion 4 .There are advantages of the perforator fl aps over muscle fl aps, mainly related to donor site morbidity, but the necrosis risk must be assessed to justify its election for fi rst choice fl aps in many fi elds, including breast reconstruction.However one aspect of these fl ap remains controversial: is lower venous outfl ow responsible for literature described partial fl ap loss?The purpose of the present study is to determine if venous supercharging has any infl uence on perforator fl ap viability.

Methods
Twenty male Wistar rats, between 250-300 g, were used in this experiment.Animals were anesthetized with ketamine and xylazine.The DIEP fl ap was marked over the abdominal wall; superiorly at the xiphoid level, inferiorly at the level of the anterosuperior iliac spines and laterally at the posterior axillary line (Figure 1).

Groups
The animals were randomly assigned for one of two groups: control and experiment.

Control Group
The DIEP fl ap harvested based on a single perforator of the right rectus abdominis muscle (Figure 2).Superfi cial epigastric vessels as well as others perforators vessels were cauterized.All dissection was performed with an surgical microscope (model G-Ni 8024,KAPS, Germany).

Experiment Group
Flap was harvested the same way as control group, except that the right inferior superfi cial epigastric vein was left intact (Figure 3).The fl ap was sutured to its bed.The fl ap was divided in 4 zones: I the area over the perforator vessels; II the area lateral to midline; III area lateral to zone I and IV the area lateral to zone II (Figure 4).

Viability assessment Laser-doppler fl owmetry
The fi rst reading of the fl ow in the fl ap was taken immediately after the fl ap incised (vasamedics, laserfl o bpm2, minessota, us) and this value was adopted as basal value.The measurements were performed daily in every quadrant of every animal

Digital planimetry
In the seventh post operative day the animals were killed and its fl aps were photographed at a 20 cm distance from the object (Canon Powershot S400, Canon, Japan).The images were captured and sent to a computer.Adobe Photoshop® was used to convert the images to bitmap and calculate the viability trhough pixels numbers.Flap viability=viable area (number of pixels)/total area (number of pixels) x100.

Statistical analysis
Mann-Whitney test was used to compare blood fl ow and Kruskal-Wallis to compare viability.

Flap viability
All animals were evaluated in 7th po regarding viability.Four animals were excluded, two in each group due to death during anesthesia performed daily to assess blood fl ow.Viability rate among control group was 44,13% and 97,38% , a signifi cant statistical difference (p=0,0006).

Laser-doppler fl owmetry
Basal values were obtained just after incising the fl ap, and daily in all four zones previously marked.The mean values of fl ow shows a similarity between groups in zone II and discrepant in zones I, III and IV, however there is no signifi cant statistical difference between groups.Analysis of fl ow daily shows a marked decrease of mean values on 3 rd and 4 th po in both groups, statistically signifi cant lower in control group (p=0,0011 and p=0,0379) (Table 1).

Perforator fl ap model
The model used in the present study was fi rst described by Oksar et al. 5 and it was based on a single perforator of the right deep inferior epigastric artery.Although Hallock and Rice 6 have described another fl ap and called it true perforator fl ap, the model used in the present study allows a complete analysis of hemodynamics and physiology.The size of the fl ap was variable, following anatomical landmarks as described by Oksar et al. 5,6 .Vascular predominance of DIEP fl ap in humans is the same as the TRAM fl ap, inferiorly based 7 .In rats the DIEP and TRAM fl aps are superiorly based (deep inferior epigastric artery) 6 .Hallock 6 debated this fact and concluded that although the TRAM fl ap is not perfectly related to the rat, the results obtained in experimental surgery can make important contributions to clinical research.

Venous and arterial supercharging
Supercharging is a procedure to increase fl ap vascularization.It can be a venous supercharching, an additional vein to increase drainage or an arterial supercharging, when an artery is added.Some authors 8 hipothesized that perforator fl aps have more venous congestion due to the size of its veins.Left inferior superfi cial vein was chosen for being the vein more contralateral to the pedicle.Sano 6 have already described increase in viability in supercharged TRAM fl aps in rats.

Laser-doppler fl owmetry
Laser-doppler fl owmetry is a non-invasive method to monitor blood fl ow in free fl aps, and blood fl ow variation is a useful tool to determine fl ap evolution, since viability is directly related to adequate blood fl ow.Blood fl ow has a great variability in every animal.Ratio of fl ow is more important to evaluate, so the fi rst measurement was determined to be the basal fl ow, as described by Hallock 6 .In the present study, blood fl ow was higher in experiment group, statistically signifi cant on 3 rd an 4 th po.

Flap viability
Digital planimetry as described by Sano 6 was performed.In the present study it was encountered 44,13% of viability on control group and 97,38% on experimental group, and the difference was statistically signifi cant (p= 0,0006).It was observed a pattern of necrosis contralateral to the pedicle, already described by others authors 5,6 .

Conclusion
The viability of the deep inferior epigastric artery fl ap is superior in the venous supercharging group.

FIGURE 3 -FIGURE 4 -
FIGURE 3 -Left: diep fl ap harvested and nourished by deep inferior epigastric perforator vessels.Right: superfi cial inferior right vein dissected and preserved in experimental group FIGURE 4 -Zone demarcation over the fl ap.Zone I, over the vascular pedicle; Zone II, lateral to midline; Zone III, lateral to Zone I; Zone IV, lateral to Zone II

TABLE 1 -
Mean fl ow values in experimental and control group.Daily measurement (ml/min/100g of tissue) Note: n -number of animals, ep -standard error, p -statistical signifi cance level.