Anatomic variations of coronary arteries: origins, branching patterns, and abnormalities

After this cadaveric study was approved by the institutional review board (IRB) of the Faculty of Medicine, Chulalongkorn University (IRB No. 667/60, approval No. 044/2017), 95 heart specimens from cadaver donors without a history of heart surgery (48 male, 47 female) from the Department of Anatomy, Faculty of Medicine, Chulalongkorn University, were collected and preserved in 10% formalin. After dissection, the dominant patterns were determined by observing the origin of the PIA. The PIA originated from RCA was classified as right dominance. PIA from CxA was classified as left dominance, and if the PIA arose from both arteries it would be classified as codominance [4]. We identified the location and number of orifices in the aortic cusps, branching patterns of the LCA, origin and number of conal arteries from the RCA, the occurrence of RPDA and its origin.

Abnormalities of coronary arteries were classified according to Angelini et al. as abnormality of origins and courses [5]. All data are presented as percentages after analyses using IBM SPSS Statistics for Windows (version 21).

The study included 95 heart specimens (mean age of donors at death ± standard deviation, 76.9 ± 13.2 years; range 34–99 years) with 48 male (78.0 ± 11.7 years; range 41–99 years) and 47 female (75.8 ± 14.6 years; range 34–96 years).

The prevalence of normal coronary artery variations is summarized in Table 1. The right dominance was the most common type of the coronary arterial system. The left and codominant patterns were found in 5% and 2%, respectively (Figure 1). One coronary orifice in each aortic cusp (dual aortic origin) was the most common. The most frequent variation was one in the left aortic cusp and 2 in the right aortic cusp. The extra orifice in the right cusp was noted as the origin of the conal artery (Figure 2).

Figure 1

Figure 2

The data of branching patterns of the LCA were collected from 93 specimens, because 2 were incomplete due to student dissection. The left main trunk normally bifurcated into AIA and CxA in 32 cases (34%). The most common type was trifurcation. MA was the additional branch. In all specimens, the first branch of the RCA was the conal artery. This artery most frequently had 2 branches (56%) and most branches originated from the RCA (Table 1; Figure 3).

Figure 3

The RPDA was found in 43 specimens (45%). All RPDAs arose from the RCA after giving the right marginal artery. In 3 specimens, RPDA branched from the RCA at the acute margin of the right ventricle (Figure 4). Most of the RPDA occurred in a right dominant pattern. The prevalence of abnormalities of coronary arteries including the anomalous origin of RCA from the left aortic cusp (Figure 5A), and the myocardial bridge are summarized in Table 2. The RCA in this anomalous case coursed interarterially between the aorta and the pulmonary trunk to continue into the coronary sulcus (Figure 5B).

Figure 4

Figure 5

A myocardial bridge was found in 62% (59 of 95 specimens). Most bridges comprised ventricular myocardium except one that was the right atrial wall (Figure 6). In these cases, after giving the right marginal artery, the RCA traveled into the right atrium wall above the coronary sulcus and emerged from the atrial wall to terminate in the right ventricle before reaching the posterior interventricular sulcus. The PIA, in this case, was derived from the CxA. The number of myocardial bridges in each specimen ranged from 1 to 4. The most common location of the myocardial bridge was situated at the AIA. The locations and number of myocardial bridges are shown in Table 2 and Figure 7.

Figure 6

Figure 7

Identification of the dominant pattern of coronary arteries has clinical importance particularly from the functional impact of myocardial ischemia [3]. The prevalence of right dominance had been reported to be 40%–80% [3, 6, 7, 8], left dominance 6.8%–18.57% [7, 9, 10], and codominance 10%–42.5% [8, 11, 12]. In the present study, the prevalence of right dominance was slightly higher than that reported previously, but left and codominance were considered to be lower. However, the codominant type was reported to be absent [6]. The inconsistency could be explained by the definition of the codominant type [7]. Moreover, dissection might not always yield the same result as radiology when evaluating the anatomy of the coronary artery [3].

In 94.7%–100%, the 2 coronary orifices were typically located in both aortic cusps [3, 13, 14]. However, additional orifices can be found in the right aortic cusp. Most of these orifices belonged to conal arteries in 33%–51% [15], and some of them belonged to the sinoatrial node artery (0.4%) [7]. The prevalence of 2 and 3 orifices in the right aortic cusp was 22%–28.81% and 0.2%, respectively [7, 10]. In the present study, there was a lower prevalence of dual aortic origin, whereas the prevalence of 2 orifices within the right cusp was similar to that reported previously [7, 10]. Moreover, the occurrence of 3 orifices in the right cusp was higher [7]. The presence of multiple orifices might cause problem and should be considered while performing the right ventriculotomy [7].

Left main trunk bifurcated into the AIA and the CxA in 50%–93.3% [6, 11, 16]. Eventually, the trunk might be terminated by trifurcation in 6.7%–46% [5, 10, 15] and quadrifurcation in 4%–10% [6, 8, 11]. In the present study, the prevalence of bifurcation was lower. Conversely, there were high percentages of trifurcation and quadrifurcation. The uncertain definition of the MA could explain these different percentages. Angelini et al. determined this artery by its distribution between the diagonal branch and left marginal artery. It may originate from the left main trunk, or proximal part of the AIA or the CxA [5], whereas some authors [6, 7, 16] as well as ourselves defined the origin of MA as only from the left main trunk. The existence of an MA might be important as a collateral vessel in cases of AIA and CxA occlusion [6, 16]. However, this artery could cause a problem while inserting a catheter and could lead to misdiagnosis [7].

The conal artery is an important in collateral circulation between the right and left coronary arteries [17]. It supplies the conus arteriosus and anterior, middle, and superior part of the ventricle [18]. The prevalence of this artery is reported as the first branch of RCA in 96%–100% [7, 10, 19]. The conal artery can originate from its own orifice in 18%–46.67% [7, 17, 19] or as a branch from the RCA in 53.34%–76% [10, 17, 19]. The number of branches varied from 1 to 3; 20%–94% of conal arteries were observed as a single branch. The double and triple branches were reported in 1%–46.67% and 6.66%, respectively [17, 19]. In the present study, the prevalence and origin of conal artery were similar to those reported previously.

The artery that could be noticed before the branching of the PIA was the RPDA. This artery irrigated the inferior part of the posterior interventricular sulcus and adjacent areas. The prevalence of RPDA was 22.1% and 14% in the right dominant type [10, 20]. The RPDA originated from the RCA in 84–86.8% and from the right marginal artery in 13.2%–16% [10, 20]. Moreover, Ortale et al. reported the prevalence of this artery in all dominant circulations [11]. In the present study, there was a high percentage of RPDA and the origin in all specimens was from the RCA. The RPDA was found in both the right and codominant types.

The anomalies of coronary arteries that have hemodynamically significance are abnormalities of the origin from the opposite sinus or pulmonary artery, myocardial bridge, and coronary fistula [21]. These might be involved life-threatening symptoms; arrhythmia, myocardial infarction, or sudden death [7]. The atypical origin of the RCA from the left sinus and from the pulmonary artery was considered to be malignantly anomalous. It has been proven that a decrease in coronary artery circulation might produce acute myocardial ischemia, arrhythmia, and sudden death [22]. This reduction in blood flow might be caused by an acute takeoff angle from the origin and the pressure effect from the interatrial course [23]. The prevalence of anomalous origin of the RCA from left sinus was observed to be 0.03–0.92% [7, 24], which was lower than that found in the present study.

The myocardial bridge comprises myocardial fibers that spread over a segment of coronary arterial branch. The bridge was determined as an atypical course that produces compression of vessels during systole. Although it may be asymptomatic in most patients during a functional stress test, a myocardial bridge might be associated with atypical angina, especially in cases with a long and deep segment [24, 25]. The prevalence of the myocardial bridge in angiography was 0.15–25% and 5–86% in autopsy reports [6, 8, 24]. Occasionally, a myocardial bridge was found at more than one site. The prevalence of single, double and triple sites of myocardial bridge were 33.33%, 8.30%, and 3.33%, respectively [26]. The middle third of the AIA followed by the left marginal artery were observed to be the most common locations [8, 15]. In the present study, the prevalence resembled that reported at autopsy. In addition, a myocardial loop formed by the atrial myocardium on the RCA was found in one specimen. This abnormality had a minimal effect on the coronary diameter. Therefore, to our knowledge prevalence of the loop has not been mentioned in any literature [25].

The prevalence of right dominance, of the coronary artery, the RPDA, the atypical origin of the RCA from the left sinus and the prevalence of a myocardial bridge were found higher than that reported previously, whereas the dual aortic origin from both cusps and the prevalence of the bifurcated left main trunk were found lower than that reported previously. Therefore, physicians should be aware of variations and abnormalities of coronary arteries when inserting catheters.