Analysis of the coronary vascular system of the chinchilla heart showed in all cases the unambiguous presence of both left (LCA) and right (RCA) coronary arteries (Fig. 1, 2).
The right coronary artery trunk ran subepicardial. The main vessels branching from the trunk were undulating. They plunged in sections deep into the heart muscle, and the subsequent side branches undulated, though definitely within the superficial layer of the muscle. Further vessels were clearly directed deeper into the muscle, giving way to brush-like branched end vessels. Observations of the left coronary artery with its branches showed a similar course. In chinchillas, epicardial fat surrounding coronary arteries is usually not observed.
The right coronary artery showed high morphological variability in the trunk, particularly in its length, its branches, and course, as well as in terms of the vascularized area (Fig. 1A-D; Fig. 2A-D). The diameter of the RCA was 0.38 mm (± 0.08). In all the examined individuals, the RCA began with an oval opening (ostium) in the right sinus of the aortic valve on the level of its sino-tubular junction (Fig. 1E). In a few cases (n = 4), the opening on the level of the aortic trunk wall was divided, giving rise to smaller additional branches of the RCA (Fig. 1A, C). In all the cases (n = 30), the RCA split by giving off one to three proximal branches and a similar number of distal branches of the right atrium (Fig. 1; Fig. 2B-D). A variable number of branches was observed around the pulmonary trunk arterial cone. In a few cases, these vessels, as small accessory coronary arteries, supplied the arterial cone or the pulmonary trunk, departing separately from the aortic trunk (Figs. 1C; Fig. 2C). Among the subsequent branches, a variable configuration of branches was observed: the right circumflex branch, the proximal intermediate and distal right ventricle branches, and the marginal branch of the right ventricle. Ventricular branches were also characterized by high individual variability, mainly related to the presence or absence of their branches (Fig. 1A-D; 2A-E).
Due to the high variability in the course of RCA regarding, inter alia, the presence or absence (Fig. 2A) of the interventricular (posterior) branch and branches of the sinoatrial node, as the determinant of coronary arteries dominance were taken the length of individual branches and the area of their vascularization. If there is a posterior interventricular artery, it is always a branch of the LCA (Fig. 3D).
These observations allowed us to distinguish the two most common variants of the RCA course. Type 1 (n = 11) consists of cases where, from the trunk of the RCA running in the coronary sulcus, the conical branch of the pulmonary trunk and the sinoatrial nodal branch that supplies the upper wall of the right atrium and the area of the sinoatrial node branched off in turn (Fig. 2B; Fig. 3C). The right circumflex branch, continued as an extension of the RCA under the right auricle towards the coronary sinus (Fig. 2B). Without reaching the subsinuosal interventricular sulcus, the right surrounding branch of RCA gave off small branches to the wall of the coronary sinus, and in the further course a variable number of right ventricular secondary branches. These vascularized the proximal third of the right ventricular wall. In this type, the marginal branch of the right ventricle and the typical subsinuosal interventricular branch were not seen (Fig. 2A).
In type 2 (n = 15) the biggest branch was the marginal branch of the right ventricle (Fig. 2C; Fig. 3A, B). This vessel followed the sharp edge of the heart and supplied the proximal part of the right ventricle wall. In a few cases (n = 3) this constituted a continuation of the distal RCA segment. In this case, the right circumflex branch was underdeveloped. The branches of the right coronary artery vascularized about three quarters of the proximal part of the right ventricular wall. The remaining distal part of the right ventricular wall was supplied by the terminal branches of an extremely highly developed septal branch extending from the left coronary artery trunk (Fig. 2D, F; Fig. 3A). In its course through the interventricular septum, this vessel, in the middle of its length, radiated branches supplying the interventricular septum. The distal part of the LCA septal branch emerged on the surface of the right ventricular wall near the apex of the heart, where it ended in numerous small ramifications within the right ventricular wall.
In a few cases (n = 3), intermediate variants were observed where the marginal and the surrounding branches were similarly developed (Fig. 1A; Fig. 2D). One case involved a fetal heart with an unusually branched RCA. In this case, the short trunk was divided into four main branches: atrial, marginal, septal, and right circumflex. This last showed a very distinct nodal branch (Fig. 2E).
The left coronary artery departed in all cases (n = 30) from the left aortic sinus at the level of the free edge of the semilunar valve and ran towards the coronary sulcus (Fig. 1A-F; Fig. 2A, D, F). The left coronary artery was the dominant vessel with respect to the RCA, both in terms of diameter and area of vascularization (Fig. 2A, F). The average diameter of the LCA trunk measured at the wall of the aortic trunk was 0.74 mm (± 0.16). The LCA in its course divided into interventricular paraconal branch, circumflex, septal and ventricular branches. A wide range of variability in this vessel was also observed regarding both the length of the trunk and the number of branches. There were no sex differentiations of the examined structures.