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INTRODUCTION
Coronary arteries establish a system of vessels that supply hearts´ metabolic requirements. During diastole these arteries are filled with blood, which flows to each cardiac structure through several branches (Crick et al., 1998; Drake et al., 2010; Iaizzo, 2015).
Multiple methods have been used to describe the coronary paths and ramifications, such as direct dissection after formaldehyde fixation Crick et al., dissectible casting after polymeric repletion (Moore, 1930; Blair, 1961; Ozgel et al., 2004; Moura Junior et al., 2009; Oliveira et al., 2010; Gómez & Ballesteros, 2013); cardiac tissue digestion with corrosive agents (Blair; Bertho & Gagnon, 1964; Roldán & Blanquez Layunta, 1982; Weaver et al., 1986), clearing with wintergreen oil (Abramson et al, 1933; Moore et al., 2008) and radiological tools applied to obtain post mortem images of the heart (Rodrigues et al., 2005). However, polymeric repletion and subsequent diaphanization of adult hearts have not been presented as a tool to compare coronary paths and/ or ramification between species. This technique can be useful for anatomy teaching Rueda-Esteban et al. (2017).
The aim of this study is to determine if repletiondiaphanization is a useful tool to improve superficial coronary anatomy visualization.
Brief anatomical description
Human (Homo sapiens), goat (Capra aegagrus hircus), bovine (Bos taurus), equine (Equus caballus), porcine (Sus scrofa domesticus), canine (Canis lupus familiaris) and feline (Felis silvestris catus) hearts were selected due to their anatomical importance in veterinary and human medicine teaching and research.
For human, the left coronary artery (LCA) divides into the anterior descending artery and the circumflex branch (CxB). Their branches supply mainly the left atrium and ventricle. In contrast, the posterior descending artery (PDA) and right marginal artery (RMA) emerge from the right coronary artery (RCA), which (along with other branches) allow blood flow to the right heart and a portion of the left ventricle (Rodriguez et al., 1961; Moore et al.; Drake et al.).
Porcine and feline LCA divides into the paraconal interventricular branch (PIB) and CxB. With other branches, these vessels supply the left atrium and ventricle. On the other hand, the subsinusoidal branch (SB) and RMA rise from the RCA. The branches of these vessels supply the right heart and a part of the left ventricle. However, in cited literature RMA is not reported for felines′ cardiac anatomy (Reighard & Jennings, 1901; Weaver et al.; Abramson et al.; Crick et al.; Gómez & Ballesteros; Rodrigues et al.; Rodriguez et al.; Sahni et al., 2008).
For bovines and equines, the RCA is called right circumflex artery (RCx) after it emerges. In both species, the LCA divides into the PIB and CxB, but SBs´ origin is different, in bovines this arterial branch is a ramification of the LCA while in equines it is from the RCA (Roldán & Blanquez Layunta; Gloobe, 1989; Budras & Budras, 2003; Ozgel et al.; König & Liebich, 2008).
In canines, the right heart is supplied by the RCA, which in its path is called RCx and originates the RMA. The left heart with part of the right ventricle is supplied by the CxA, PIB and SB; branches of the LCA (Moore; Besso Pianetto, 1939; Blair; Oliveira et al.; Evans & De Lahunta, 2013). Goats´ coronary anatomy share distribution similarities with canines; however, RCx is not reported in them (Yang et al., 1989; Moura Junior et al.).
Finally, the septal arteries cross the interventricular wall supplying it. In canine, bovine and goat this vessel has been reported as a unique artery; while in human, porcine, equine, and feline it is defined as an anastomosis of branches from the LCA and RCA (Abramson et al.; Bertho & Gagnon; Yang et al.).
MATERIAL AND METHOD
Seven adult hearts, one of each species, were used for this study. Age, size, weight and sex were not considered relevant. The human heart was acquired at the Universidad de los Andes School of Medicine Anatomy Laboratory, under the Research Ethics Board Act No. 448 of 2015 and the Expedited Endorsement for cadaveric dissection and description Act No. 518 of 2015. Porcine, bovine, and goat hearts were obtained as products of food industry. Canine, feline, and equine specimens were obtained after euthanasia due to medical conditions with the appropriate indication of this procedure, non-related to this study. Animal specimens were used under the approval of our Institutional Animal Care and Use Committee (IACUC) (Reference: CICUAL_17-021).
Repletion was carried out by injecting methylmethacrylate through the coronary arteries, beginning at the ascending aorta. The injection of the atrial and ventricular cavities was not required. Fixation and dehydration were done by submersion in ethylic alcohol at increasing concentrations until 96.9 % was reached. Diaphanization was then carried out in all specimens following our Anatomy Laboratory protocol Rueda-Esteban et al. Potassium hydroxide (KOH) at an initial concentration of 4-5 % was used to macerate the tissue. Then, the hearts were cleared with anhydrous glycerin and KOH, varying the glycerinKOH proportion until the specimen was totally immersed in glycerin. Finally, pictures of the hearts were taken, and the background was eliminated with Macromedia Fireworks 8 and Adobe Photoshop 10, without editing the hearts.
RESULTS
All hearts were successfully injected, six of them were partially diaphanized (bovine, equine, porcine, canine, human and goat) and one fully diaphanized (feline). Despite this, in some species the epicardial fat distribution didn´t allow proper visualization of some coronary arteries (Fig. 1). The observed anatomy was concordant with the literature, however as incidental findings, two anatomical variations were found: in the human heart, the PDA emerged from the LCA; in canine heart, the SB was a branch of the RCA.
DISCUSSION
Big hearts need a longer maceration time to complete the diaphanization process. However, coronary paths and its relationship with other cardiac structures can be seen through partial diaphanization. For Bovine and equine hearts, the CxB and RCx cannot be easily visualized because they are surrounded by epicardial fat (Fig. 1), which can be removed through dissection before the diaphanization process, not pursued for this study. Septal arteries are not correctly visualized through this technique, since full maceration is necessary, increasing the risk of tissue damage.
By blending the approaches of repletion to highlight coronary vessels and transparency obtained through diaphanization (even if partial), repletion-diaphanization proves to be a useful tool to observe main superficial coronary arteries without damaging related cardiac structures and three-dimensional arrangement of the heart. The use of this type of specimens could be a valuable tool for teaching and research purposes. Further research should be done to determine its functionality and shelf life.
