Ex vivo model with bovine heart : a proposal for training microscopic dissection and vascularmicroanastomoses

Training is a process that requires patience and constant practice. The execution of microscopic procedures is present in the day-to-day of several surgical specialties, but unfortunately experimental models are not easy to access in our environment. We propose a bovine heart model used by residents and young surgeons in the training of microscopic dissection and microanastomoses. It is described the assembly of this model, which can be performed individually and with accessible material to the surgical departments. Our experience in the preparation of the pieces, as well as tips for the process, are described in the text. The bovine myocardial model can be reproduced in any center with benches and surgical instruments. Low cost, fast preparation, and wide availability of the used tissue are among the advantages of this model. We consider the project useful in the training of surgical residents and young surgeons.


M
icrosurgery is a routine of many surgical specialties, such as Neurosurgery, Reconstructive Plastic Surgery, Vascular Surgery, Cardiac Surgery and Otorhinolaryngology, among others.There are several models described in literature to train microsurgery in experimental environment, employing from synthetic materials, such as plastics and latex, to biological ones -such as corpses [1][2][3][4][5] .
These factors are important in this context of microsurgical models: cost 6 , time for replication, basic instrumental for reproduction, similarity with structures and environments found in surgical procedures, comparison and evaluation of training results 7,8 , applicability of developed ability 9 , use of inert materials, use of guinea pigs and their bioethical issues 10 , and guidance or supervision during the execution of activities 11 .
We present a model of easy reproducibility and low cost for microsurgical training, using bovine heart.This model allows to perform microanastomoses and to exercise necessary fine movements with microsurgical instruments.The advantages and disadvantages of this model are also related in the text.

TECHNICAL NOTE
For the model, we used fresh bovine hearts, in which the following procedures were performed: selective catheterization of the coronary arteries, perfusion and removal of clots followed by saline solution infusion containing dyes in a ratio of 4:1.
For such method, the traditional quenching ink, which has the advantages of easy appearance for dissection and have already been used in other works in literature.Figures 1 and 2 show the used instruments, the piece assemblies, and the initial work of the dissection of the vessels.
The cardiac muscle was sectioned and extended, which generated more stability to work (Figure 3).
After coronary dissection, extensions from 2cm to 3cm free from perforators in the course of vessels may be found.Larger space to perform microanastomoses could be obtained by ligating perforators.Nylon 9-0 and 10-0 suture wire were used to perform end-to-end, end-to-side, and side-to-side anastomoses, these with the use of sectioned vessels of the piece itself or of other myocardiums (Figures 4 and 5).The execution is performed with the help of a surgical microscope with magnification ranging from 10x to 14x.In our laboratory there was a Zeiss S88 microscope available for training.In general, from six to ten knots were required for an integral suture, varying with the diameter of the vessel.In more proximal stretches, coronaries with up to 3mm diameter may be found, while in more distal areas in the piece most vessels are up to 1.5mm in diameter.Then, the surgeon tests the permeability of communication with the diluted dyes.In addition to anastomoses, direct sutures could also be trained in more gibbous parts of the vessels, as shown in figure 4.An important aspect in anastomoses is the patency after vessel suturing.The use of dyes after luminal catheterization has been already successfully described in a variety of organs or tissues.Among them, placenta, rat cadavers, and even human parts in anatomical laboratories 3,8 .In this project, the injection of saline with ink allowed the surgeon good visibility of the flow through the anastomosis and, in case of absence of patency or externalization of the content, the correction could be made instantly, observing the result of new knots or their withdrawal.We mentioned the dilution we usually use, but, if the practitioner desires a more consistent appearance of the solution, the dye/ ink ratio should be increased.More concentrated mixtures leak less through sutures or damaged tributaries.Training centers with this resource availability should encourage their residents to take full advantage of this opportunity 5,15 .Works with femoral vein and carotid artery are the most cited in literature 6,16 .
However, the model of this article presentes other relevant advantages.As already mentioned, its cost was lower when compared to living animal models, for which it is necessary, in addition to the direct acquisition, budget for animal husbandry, anesthesia material, and postoperative support.Regulation and bioethical considerations are not a problem for the training centers, since the pieces are easily obtained by any citizen and care should always be taken only with proper disposal in the laboratory.Finally, in relation to inorganic (for example, latex 13 ) models, the use of animal tissue offers greater similarity to human surgeries, regardless of the topography or surgical area.

Figure 1 .
Figure 1.a) instruments for microsurgical training, using a bovine heart model: micro-scissors, fine tweezers, needle holder for macroscopic suture and in bayonet for microscopic suture, catheters, and syringes.Inks added to saline solution were used as dyes.The preparation of the model was carried out on a simple lab bench; b,c) initial intraluminal vessel wash to eliminate debris was performed.Initially, a needle gave greater pressure to clean vessels with coagulated blood.Then, a micro-catheter was used to infusedye.

Figure 2 .
Figure 2. a) catheter positioned for dye injection; b) distal vessels are less gibbous and have more tributaries; c,d) magnified dissection with the aid of blue dye for better identification of planes and perforators.

Figure 3 .
Figure 3. a) sectioned and extended piece of bovine myocardium (larger) to execute the model.Piece of porcine myocardium (smaller) was also tested in the formulation of the proposed model.The porcine piece, despite having less adipose tissue, has smaller area for the dissection work and for micro-suture; b) piece of bovine myocardium with excess of fatty tissue.Such type of piece is commonly found in meat shops and can cause difficulty in the elaboration of the model, if unawarely acquired.

CONCLUSIONS
Surgeons naturally obtain satisfactory results in the day-to-day routine due to the repetition of the dissection process, identification, and microsuture practice.To reach this point, it takes determination and patience during training period.As coordinators of this project, we aimed to demonstrate an objective and reproducible method to collaborate in the development of the microsurgical practice.This model serves as a facilitator for supervised learning during the medical residency, or even for the constant exercise of microvascular technique by specialist surgeons.In Brazil, residents usually lack time or financial conditions to seek a more refined training or even have access to structured laboratories.As described, the use of bovine heart is cost-effective and can help in this preparation stage to work with microstructures and perform vascular surgeries in a valuable way.