INTRODUCTION

Knowledge of the individual variants of coronary artery structure is crucial for the successful diagnosis and surgical treatment of coronary sclerosis (Bokeriya & Berishvili, 2003). For nearly a century, interest in the study of heart arteries has persisted due to the high mortality rate from angina and myocardial infarction (James, 1961; Kolesov, 1977; Sokolov, 2005; Muresian, 2009). The type of coronary artery distribution and their branches determine the conditions of heart blood supply and the compensatory restoration of blood flow in cases of acute myocardial ischemia.

M.S. Lisitsyn (1927) was one of the first to propose distinguishing three types of coronary artery structures: right-dominant, left-dominant, and balanced patterns. This classification is based on the distribution of branches from the circumflex branch of the left coronary artery and the right coronary artery on the diaphragmatic surface of the heart. Later, other anatomists proposed different approaches for classifying heart arterial architecture types (Schlesinger, 1940; James, 1965). These included determining the ratio of the diameters of the circumflex branch of the left coronary artery and the right coronary artery, counting the number of arterial branches to the heart chambers, measuring the angles of branch departure depending on the heart shape, and determining the methods of coronary artery branching (Lüdinghausen, 2003; Loukas et al., 2009; Goryacheva, 2012; Milyukov & Zharikova, 2014). However, these methods proved to be more labor-intensive and less accurate, which is why they did not gain wide practical application. These additional morphological indicators should be considered only within the framework of the main topographic types of coronary artery structures: balanced, right-dominant, and left-dominant. Recently, morphological data have been supplemented by clinical studies of heart vessels using contrast-enhanced computed tomography, which allows for the identification of the three-dimensional orientation of coronary arteries, the anastomoses between them, and the evaluation of the actual blood supply zones of the atria and ventricles. However, anatomical methods for determining heart arterial structures remain more accurate and objective.

The definitive angioarchitecture of the heart develops during its intrauterine development. During the embryonic period, coronary arteries form as a network of rings. Subsequently, several arteries become major vessels, while the remaining small arteries do not undergo further development, after which the branching and distribution of the coronary vessels becomes unique for each heart (Berishvili & Vakhrormeeva, 1990). The reduction of the right or left half of the initial arterial network will ultimately determine the topographic type of blood supply in adults. Such a causal approach excludes mechanical interpretation of coronary artery structure variants and makes it conscious and scientifically grounded.

This study was conducted to determine the frequency of different types of coronary artery structures in the human heart, and to identify the most effective and least labor-intensive method for studying cardiac vessels.

MATERIALS AND METHODS

The study was conducted on 78 hearts obtained from deceased individuals of mature and elderly age. Based on the research method used, all hearts were divided into three groups. The first group consisted of nine hearts, where the heart vessels were studied by dissection after preliminary fixation in 7% formalin solution for 2 weeks, without prior injection. In the second group, consisting of 37 specimens, the heart arteries and veins were injected with a colored silicone composition (comprising 100 parts of low-molecular-weight silicone with hydroxyl groups SCTN-A, 4 parts of tin-organic catalyst K-18, and 1 part of organic dye) before fixation. After silicone polymerization, the hearts were fixed in 7% formalin for 2 weeks and then studied by dissection to examine the topography of the injected arteries and veins. After determining the type of coronary artery structure, the hearts from the first and second groups were plastinated with silicone using the room temperature plastination method (Starchik & Henry, 2019). In the third group, consisting of 32 unfixed hearts, after flushing the atria and ventricles with warm water, silicone tubes of the appropriate diameter were inserted into the superior vena cava and one of the pulmonary veins, while the remaining large heart vessels were ligated or clamped. A mixture of 100 parts of high-molecular-weight silicone SCTN-G (Penta Co. Ltd)., 1 part of catalyst K-18 (Penta Co. Ltd.), and 1 part of organic dye (blue for the right chambers and heart veins, red for the left chambers and coronary arteries (Penta Co. Ltd.)) was injected under low pressure into the inserted tubes. After injection and silicone polymerization, the solidified casts of the right and left heart chambers were joined using long metal pins. To prevent displacement of artery and vein casts during corrosion, the injected vessels were also attached to the silicone casts of the heart chambers with small metal clips. Soft tissue removal was carried out by placing the specimens in a 25% sodium hydroxide solution heated to 70º C for two hours. The resulting corrosion casts of the heart chambers and vessels were rinsed in running water for 30 minutes, air-dried, and then studied and photographed.

The topographic type of coronary arteries was characterized by several criteria: 1) the distribution area of the right coronary artery (RCA) and the circumflex branch of the left coronary artery (LCACB) on the diaphragmatic surface of the heart; 2) the length, diameter, and branching pattern of the RCA and LCACB branches on the diaphragmatic surface of the heart (long, short, simultaneously long and short, short and "diving" branches); 3) the degree of arterial trunk formation on the diaphragmatic surface of the heart (strongly trunked network consisting of 2-3 arteries; moderately trunked network of 4-6 vessels; weakly trunked network of 7-10 arteries).

RESULTS

The left coronary artery (LCA) originated from the ascending aorta at its left sinus and immediately divided into branches. There were several branching patterns: 1) the LCA divided into two vessels - the anterior interventricular branch and the circumflex branch (81%); 2) the LCA divided into the anterior interventricular branch and a short trunk, which gave rise to the left marginal and circumflex branches (10%); 3) the LCA divided into three vessels: the anterior interventricular, diagonal, and circumflex branches (1%); 4) the LCA divided into a short trunk (for the anterior interventricular and diagonal branches) and the circumflex branch (8%). The first branching pattern of the LCA was the most common.

The right coronary artery (RCA) originated from the right sinus of the ascending aorta and was located in the right coronary sulcus. Initially, it gave off branches to the sternocostal surface of the heart - the right conus branch, the branch to the sinuatrial node, atrial branches, the anterior right ventricular branch, and the right marginal branch (inconsistent), then continued along the coronary sulcus to the diaphragmatic surface of the heart.

Based on the results of the heart studies in all examined groups, three types of coronary artery distribution were identified: balanced, right-dominant, and left-dominant. The main morphological criterion for determining the type of coronary artery structure was the distribution of the circumflex branch of the left coronary artery and the main trunk of the right coronary artery on the diaphragmatic surface of the heart.

In all examined heart groups, the balanced type of coronary artery distribution was the most frequently identified, with a frequency of 59.0%, while the left-dominant type was the least frequently observed. The results of the determination of artery branching types are presented in Table 1.

The balanced type of coronary artery distribution was identified in 46 out of 78 hearts examined. This type was characterized by the approximately equal diameters of the right coronary artery (RCA) and the left coronary artery (LCA), which did not exhibit significant signs of reduction. In this distribution pattern, the circumflex branch of the LCA branched within the diaphragmatic surface of the left ventricle, giving rise to 2-4 small diameter branches that extended to the posterior part of the interventricular septum. Meanwhile, the RCA followed the right portion of the coronary sulcus, descending along the posterior interventricular sulcus to the apex of the heart, where it gave off 2-5 small diameter branches to the posterior surface of the left ventricle (Fig. 1).

Figure 1. Balanced type of coronary artery distribution. A – plastinated specimen without coronary artery injection; B – plastinated specimen with injected coronary arteries; C – corrosion cast of the heart chambers and vessels. 1 – circumflex branch of the left coronary artery; 2 – right coronary artery; 3 – posterior interventricular branch; 4 – posterior branch of the left ventricle

In the balanced type, the posterior branches of the left ventricle always originated from the circumflex branch of the LCA. Besides these branches, the LCA often gave rise to the anterior branch of the left ventricle, atrial branches, and the left conus branch. The LCA branched in the anterior zones of the interventricular septum, left ventricle, and left atrium.

For the RCA, in the balanced type, it followed the diaphragmatic surface of the heart, giving off the posterior branch of the right ventricle and continuing to the posterior interventricular sulcus, where it became the posterior interventricular branch. The branching of the RCA was trunk-like, with all branches originating from the main arterial trunk and having relatively small diameters. The RCA branched in the myocardium of the posterior third of the interventricular septum, right ventricle, and right atrium.

In rare cases (approximately 10%), the RCA and LCA connected in the coronary sulcus, forming a pronounced coronary arterial anastomosis that closed the arterial ring in the coronary sulcus on the posterior surface of the heart. Such a coronary artery structure variant evidently provides more favorable compensatory possibilities for the development of collateral blood circulation in the heart.

A closed interventricular arterial anastomosis, where the anterior interventricular branch from the LCA anastomosed with the posterior interventricular branch from the RCA at the apex of the heart, was recorded very rarely, in less than 5% of observations.

 The right-dominant type of coronary artery distribution was observed in 28.2% of all cases. This type is characterized by an increase in the diameter and distribution area of the RCA. In this type, the circumflex branch of the LCA was partially reduced and did not reach the posterior interventricular sulcus, thereby leaving the right part of the diaphragmatic surface of the left ventricle available for the RCA branches (Fig. 2). A characteristic feature of the right-dominant type is also the predominance of the RCA diameter over the LCA diameter at their origin from the ascending part of the aorta.

Figure 2. Right-dominant type of coronary artery distribution. A – plastinated specimen without coronary artery injection; B – plastinated specimen with injected coronary arteries; C – corrosion cast of the heart chambers and vessels.
1 – circumflex branch of the left coronary artery; 2 – right coronary artery; 3 – posterior interventricular branch; 4 – posterior branch of the left ventricle

We identified two variants of the right-dominant type of coronary artery distribution: the moderate and the extreme. These variants differ in the degree of reduction of the LCA and the size of the right-dominant network distribution area on the posterior surface of the left ventricle.

The moderate right-dominant variant was more common, where the circumflex branch of the LCA was slightly reduced, giving off the left marginal branch to the left pulmonary surface of the left ventricle and the posterior branch of the left ventricle to the left half of its diaphragmatic surface. In this variant, the RCA branches were distributed over no more than 50% of the diaphragmatic surface of the left ventricle.

The extreme right-dominant variant differed from the moderate right-dominant variant in that the left-dominant network was more significantly reduced. This was evident in the absence, or significant underdevelopment, of the circumflex branch of the LCA. The circumflex branch originated from the LCA along with the anterior interventricular and diagonal branches, continuing into the left marginal branch without entering the diaphragmatic surface of the left ventricle, where the RCA branches were distributed.

In any variants of the right-dominant type, the RCA on the diaphragmatic surface of the heart formed a circumflex branch that continued along the left half of the coronary sulcus nearly as far as the pulmonary surface of the left ventricle, giving off several posterior branches of the left ventricle to its myocardium.

In the extreme right-dominant variant, the RCA on the diaphragmatic surface was seen to divide in two ways: 1) into two branches: the posterior interventricular branch (from which the right circumflex branch originates) and the posterior branch of the left ventricle; 2) into three branches: right circumflex, posterior interventricular, and posterior branch of the left ventricle. The right circumflex branch occupied the entire left half of the coronary sulcus. The posterior branch of the left ventricle originated directly from the RCA trunk or the right circumflex branch (Fig. 2A). The coronary network in this variant consisted of a trunk RCA with short and long branches, diving into the myocardium.

Thus, in the extreme right-dominant type, the RCA branches were distributed over more than 50% of the posterior surface of the left ventricle. The circumflex branch of the LCA was significantly reduced.

The left-dominant type of coronary artery distribution was the least common, observed in only 12.8% of cases. This type is characterized by the predominant development of the LCA and underdevelopment of the RCA (Fig. 3). In this distribution pattern, there could be two circumflex branches of the LCA. The main circumflex branch occupied the entire left section of the coronary sulcus and formed the posterior interventricular branch, which is an atypical branching pattern for the LCA. The additional circumflex branch followed below the main one, was short, and continued into the posterior branch of the left ventricle. When there was only one circumflex artery, it gave off several posterior branches of the left ventricle along its course and continued into the posterior interventricular branch.

Figure 3. Left-dominant type of coronary artery distribution. A – plastinated specimen without coronary artery injection; B – plastinated specimen with injected coronary arteries; C – corrosion cast of the heart chambers and vessels. 1 – circumflex branch of the left coronary artery; 2 – right coronary artery; 3 – posterior interventricular branch; 4 – posterior branch of the left ventricle

In comparison to the LCA, the RCA in the left-dominant type had a significantly smaller diameter and a shorter length, not exceeding 5 cm, which is much less than in other types of coronary artery distribution. The RCA originated from the ascending part of the aorta, passing in the coronary sulcus on the sternocostal surface of the heart, and continued into the right marginal branch, which ended at the right edge of the right ventricle and did not branch on the diaphragmatic surface of the right ventricle. Consequently, the branching region of the RCA was significantly smaller than in other types. Thus, in the left-dominant type of coronary artery distribution, the LCA occupied its typical region, which included the posterior region of the interventricular septum and part of the diaphragmatic surface of the right ventricle and right atrium.

DISCUSSION

The use of surgical methods to treat ischemic heart disease requires precise data on the types of coronary artery system configurations. Despite significant advances in in vivo imaging methods, such as coronary angiography and contrast-enhanced computed tomography, anatomical methods remain essential for determining coronary artery distribution types. The approaches proposed by Lisitsyn (1927) and Schlesinger (1940) for identifying the distribution types of the left and right coronary artery branches on the diaphragmatic surface of the heart have gained wide acceptance in anatomy and cardiovascular surgery. These approaches allowed the classification of three types of coronary circulation: right-dominant, left-dominant, and balanced patterns. Modern researchers utilize additional criteria for determining coronary artery structure types, specifically: 1) the initial diameter and topography of the circumflex branch of the left coronary artery and the right coronary artery; 2) the degree of formation of arterial trunks at the intersection of the coronary sulcus with the posterior interventricular sulcus; 3) the length and diameter of the branches of the right and left coronary arteries in the area of ​​the posterior interventricular sulcus and the apex of the heart; and 4) the area of ​​distribution of the branches of both coronary arteries in various regions of the posterior surface of the left and right ventricles. The use of all these criteria has led to the emergence of several subtypes within each coronary artery structure type. In our view, such a complex classification, utilizing additional varieties, requires strict quantitative, rather than qualitative, criteria for coronary artery distribution, including methods that can identify small coronary artery branches located deep within the myocardium. Moreover, these complex classifications often lead to varying interpretations, and complicate the comparison of results obtained by different researchers. Therefore, in our work, we used a simple classification with three types of coronary artery distribution, categorizing them into right-dominant, left-dominant, and balanced patterns.

The results of coronary artery distribution type determination vary significantly among researchers. According to our data, the balanced type of coronary artery distribution was the most common, occurring in 59% of cases, which is consistent with the data of other authors (Ahmed et al., 1972; Dzhavakhishvili et al., 1982; Koizumi et al., 2000). The balanced distribution pattern is associated with the presence of numerous anastomoses between the branches of the right and left coronary arteries in the posterior interventricular septum. However, many cardiac surgeons note that the existing anastomoses between the coronary artery branches are insufficient during myocardial ischemia and cannot ensure collateral blood flow in the event of acute coronary circulation disorders (James, 1961; Bokeria & Berishvili, 2003).

Most other researchers (Schlesinger, 1940; Blunk & DiDio, 1971; Pino et al., 1987; Falci Júnior, 1996; Karpov et al., 2010; Savchenko et al., 2010; Ortale, 2004) considered right coronary artery dominance to be the most common variant, with frequencies ranging from 48% to 78%. The frequency of the right-sided distribution type found in our study was 28.2%, which does not match the results of the above-mentioned authors.

Left coronary artery dominance was identified in only 12.8% of all our observations, making it the rarest variant of coronary arterial architecture. This aligns with the findings of the majority of coronary artery researchers. Those researchers who described the left-dominant type as the most common (James, 1965) did not base their classification on the distribution of coronary arteries on the diaphragmatic surface of the heart, but rather on the volume of myocardium supplied by each coronary artery. This classification approach may be valid but is rarely applied in morphology.

The application of various morphological methods for identifying coronary artery branching types enabled us to compare their effectiveness in determining arterial distribution zones in the heart chambers, the complexity of execution, and the overall labor intensity of each technique used. According to our data, the most effective but also the most labor-intensive method was the dissection of coronary arteries following the injection of colored silicone masses (hearts from the second group, Figures 1B, 2B, 3B). This technique has been widely used by other authors (Baptista et al., 1988; Goryacheva, 2012; Milyukov & Zharikova, 2014). For the injection, special metal cannulas were inserted into the coronary artery openings through the ascending aorta. For the injection of the heart veins, plastic tubes of various diameters were inserted into the coronary sinus opening and secured with surgical sutures. On average, injecting one heart took about 50 minutes. The zones of distribution of the right and left coronary arteries could be determined by the color of the myocardium in the branching zone, making it advisable to use silicone compositions of different colors for the right and left coronary arteries. Subsequent dissection after silicone polymerization involved removing subepicardial fat and loose connective tissue from the surfaces of the arteries and veins. It was noted that venous injection was not necessary for determining the coronary artery branching type, as it did not affect the result.

Silicone injection improves the results of dissection even of small-diameter arteries, significantly facilitating the identification of the distribution area of coronary artery branches compared to the hearts of the first group, where vascular injection was not used (Figures 1A, 2A, 3A). Dissection of arteries without prior injection was more commonly used in the first half of the 20th century (Lisitsyn, 1927; Schlesinger, 1940) when polymers were rarely used in anatomical practice for vascular injection, although coronary artery studies without injections are still encountered in the 21st century (Koizumi et al., 2000; Ortale, 2004). In hearts without prior artery injection, it was more challenging to determine the branching area of small-diameter arteries and to identify arteries passing deep within the myocardium. After silicone plastination, non-injected heart vessels often appeared collapsed and deformed. We used silicone plastination of the hearts from the first and second groups to preserve the studied samples for extended periods, enabling their further use for more detailed analysis and educational purposes.

Corrosion methods for obtaining vascular and heart chamber casts, followed by determining the type of arterial distribution, were employed in scientific research by James (1965) and Ahmed et al. (1972). This technique allows for easy visualization of large and small coronary artery branches on the surface of silicone heart chamber casts (hearts from the third group, Figures 1C, 2C, 3C), eliminating the need for labor-intensive dissection of heart vessels. However, using the corrosion method requires careful removal of the heart from the thoracic organ complex to avoid damaging large vessels and heart chambers. Thorough removal of blood clots and thrombi from the heart cavities with a stream of warm water was also crucial for obtaining good results. During injection, attention must be paid to ensuring the penetration of the silicone composition into the smallest arteries and veins, which is achieved by injecting under significant pressure. The injection of the silicone composition into the heart chambers under pressure increases the volumes of the heart chambers but does not alter the topography of the cardiac vessels. Since the resulting casts can shift during the removal of soft tissues in hot alkali, the fixation of the polymerized casts of the heart chambers to each other and the attachment of large arteries and veins to their surfaces with metal pins and clamps was crucial for preserving the original topographic relationships. After the corrosion process, determining the coronary artery branching type was not difficult, as the chamber boundaries and the distribution zones of the right and left coronary artery branches were easily identifiable on the casts.

CONCLUSION

Thus, the most common pattern of coronary artery distribution is the balanced type, followed by the right-sided pattern, with left coronary artery dominance being the rarest. All three plastination methods used can be applied to study coronary artery branching types; however, the least labor-intensive and most informative method is the use of the corrosion technique to obtain casts after the separate injection of red silicone composition into the left heart chambers and coronary arteries, and blue composition into the right heart chambers and veins, followed by corrosion.