Investigación original

Sino-atrial node artery variation in a sample of the Colombian population

Yobany Quijano-Blanco¹, Ricardo Luque-Bernal², Diana Escobar-Gutiérrez³, Luis E. Caro-Henao⁴

¹ MD. Universidad de Ciencias Aplicadas y Ambientales. Profesor de Anatomia Facultad de Medicina UDCA, Especialista en docencia Universitaria Universidad Militar Nueva Granada. MSc. Morfología Humana, Universidad Nacional de Colombia.
² MD. Universidad Nacional de Colombia. Profesor de Anatomía Facultad de Medicina, Universidad de Ciencias Aplicadas y Ambientales. MSc Genética Humana, Universidad Nacional de Colombia.
³ Bacterióloga, Universidad Colegio Mayor de Cundinamarca. MSc Educación, Pontificia Universidad Javeriana.
⁴ MD. Profesor de Morfologia, Universidad Nacional de Colombia.

Correspondencia: globdimorf@udca.edu.co

Recibido: 11/12/11/ Enviado a pares: 06/02/12/ Aceptado publicación: 15/02/12/

Summary

Background. Accurate knowledge regarding the cardiac conduction system's anatomical-physiological integration is essential for understanding the pathophysiology, diagnosis and management of many complications regarding coronary disease and heart disease in general. One of the more variable fundamental aspects, having the greatest clinical impact, concerns the origin and course of arteries irrigating the sino-atrial node (SAN).

Objective. Determining the origin, course and distribution of arteries supplying the SAN in a sample of the Colombian population.

Materials and methods. 60 cardiopulmonary and digestive blocks were taken by convenience sampling. Conventional dissection of the genitalia determined gender; the coronary artery was then dissected, specifically the SAN, to establish origin and route.

Results. It was found that 75% of the SAN artery's blood supply came from the right coronary artery (RCA), 15% from the circumflex artery and 10% was co-dominant. 86.6% of courses were linear; 13.4% were Y-shaped or Y-and double trident shaped.

Conclusions. The prevalence of SAN artery origin in the RCA in this study was consistent with similar research findings, regardless of geographical and racial origin. However, this study report some courses not previously described in the literature, such as Y-, double Y-, inverted K- and trident-shaped forms.

Key words: blood supply, sinoatrial node, coronary occlusion, heart conduction system, arrhythmias, cardiac, death sudden (MeSH).

Introduction

The cardiac conduction system involves a large part of the myocardium and includes the sinoatrial node (SAN), the atrio-ventricular node, the bundle of His with corresponding left and right bundle branches and the Purkinje fibres (subendocardiac branches). The SAN is fundamental for the heart's functioning as it potentiates action thereby providing physiological cardiac rhythm (1,2) and transmitting the electrical impulse which (after coursing through the conduction system) couples to the cardiac muscle through intercalary discs to make the latter contract (3).

A right and a left coronary artery originate from the aortic root; this is occupied by the aortic sinuses in which such arteries have their outlet orifices (4,5). The right coronary artery (RCA) originates in the right aortic sinus and the left coronary artery (LCA) in the left aortic sinus (6). Even though the coronary arteries provide a constant run/supply, multiple anastomoses may be presented between them thereby allowing a blood supply to be maintained to the myocardium in the event of stenosis, thrombi or embolisms (4,6,7). These arteries' origins may vary significantly regarding the sinutubular junction and their proximity to apposition areas between heart valve leaflets (8-10). Some reports in the literature have shown that the anterior interventricular and the circumflex (Cx) arteries emerge independently in the left aortic sinus on some occasions (7,8,10).

Reports in the pertinent literature have stated that the SAN artery may originate in either the RCA or LCA (2); however, distribution percentages regarding the origin of such artery in a particular population are not clear since there is broad variability cording to the particular population being studied. The coronary artery originating SAN irrigation for the heart's suitable functioning is called the dominant coronary artery. The SAN artery's origin varies according to its trajectory but, in all cases, it must reach the extreme posterior of the right atrium's anterolateral (i.e. sinus) wall, adjacent to the superior vena cava' outlet where the SAN is located (2,9).

The conduction system is located in the myocardium; it is formed by specialised cardiac cells controlling cardiac frequency and synchronising myocardial tissue's rhythm and contractions to ensure an optimum cardiac cycle (1, 11-14). This cardiac conduction system is a complex and intricate network of myocardial tissue specialised in conducting and transmitting action potential through intercalary discs, thereby allowing them to communicate with each other and thus ensure that the myocardium behaves like a syncytium. This begins with a specialised structure in the right atrium's upper and anterior walls, located below the superior vena cava's outlet; such structure, called the sino-atrial node (SAN), is located in the subepicardium and is situated in the junction between the musculature its base is midway opposite the terminal crest, towards the lower third of the right atrial wall (11,12,14).

Few studies have been carried out in Colombia regarding the irrigation of the cardiac conduction system; this contrasts with the international literature which contains many investigations related to coronary artery distribution. Such studies have revealed great diversity regarding cardiac conduction system irrigation artery distribution and origin, many highlighting the SAN artery (4,5,9). The Colombian population's anatomical variations must thus be described, since such population's unique characteristics regarding their ethnic composition (15), extrapolating prior studies concerning SAN anatomical structure and variations and the coronary circulation branches involved in their irrigation are questionable. The present study was thus aimed at describing the SAN artery's anatomical origin, distribution and variations in a sample of the Colombian population.

Materials and methods

Type of study: an analytical, descriptive study was made using quantitative methods.

Sample: 60 cardiopulmonary and digestive surgical blocks were selected by convenience sampling. Hearts presenting congenital cardiac malformations, evident chronic cardiopathy or signs of pathology or cardiac traumas producing morphological alterations of the heart were excluded from the study following such exploration.

Methods: the coronary arteries of 60 human hearts were dissected, specifically seeking arteries irrigating the SAN. The epicardium was removed and the right and left coronary arteries referencing the space between the outlet of the superior vena cava and the right atrium's posterosuperior face. All the arteries leading to such region were then dissected from the right and left coronary arteries, identifying possible candidate arteries, selecting that whose anatomical route was closest to the aforementioned region as the SAN artery. The region having the artery was photographed and a diagram made.

Ethical component: the material for dissection was obtained strictly in line with the criteria defined for medical-legal autopsies, as contained in decree 786/1990 (17).

All the principles regarding medical research in the Declaration of Helsinki (2000) were followed, thereby guaranteeing respectful treatment of the pieces obtained during the study, the confidentiality of data regarding the dead people, their dignity and integrity.

Colombian Ministry of Health resolution 8430/ 1993 (18), article 16, first paragraph, states that an ethics committee may exempt an investigator from obtaining informed consent in investigations involving minimum risk or no risk.

Results

Conventional dissection of the genitalia determined that 3 of the 60 surgical blocks came from females and 57 from males.

It was found that 75% of the SAN artery's blood supply came from the RCA, 15% from the Cx artery, LCA branch and 10% was co-dominant from both the RCA and the Cx.

Regarding the anatomical distribution and route of the artery irrigating the SAN, its origin and termination in the anterolateral-posterior face of side and 20.1% to the left) (Figure 1), 8.3% cothe right atrium was taken into account; 78.3% dominant right- and left-hand side lineal and 8.3% single lineal branch (80.9% towards the right-hand Y-shaped on the right-hand side (Figure 2).

The following anatomical distributions were also found (1.7% in each case):
- Three trident-shaped lineal branches (Figure 3);
- Right double Y-shaped branch (Figure 4); and
- Right inverted K-shaped branch and codominant left lineal (Table 1).

Discussion

Dissecting 60 cardiopulmonary and digestive blocks led to describing the irrigation of the SAN in this particular sample of the Colombian population, showing that 75% of the SAN arteries came from the RCA, 15% from the Cx artery and 10% from the RCA and Cx artery (i.e. codominant irrigation). Such results contrasted with work by Ballesteros et al., (25) who studied 88 hearts using a corrosion injection technique; they reported 59,1% origin in the RCA, 37,3% in the Cx and 3,4%.

Co-dominant. Ramanathan et al., (29) studied 300 patients from southern India; they identified SAN irrigation by coronary angiography, finding that the SAN received 53% of its supply through the RCA, 42.66% by LCA Cx branch and 4.33% by both coronary arteries.

RCA dominance was also observed in studies by Silva et al., (8), Berdajs et al., (16), Kyriakidis et al., (19), Futani et al., (20), Sow et al., (22), Okmen et al., (24) and Caetano et al., (26) where percentages similar to those dominance was greater in more than 50% of the population samples. Conversely, Ramanathan et al., (29), Ortale et al., (27) and James (28) did not show clear dominance by either coronary artery (Table 2).

RCA dominance has also been reflected in studies by Silva et al., (8) in Río de Janeiro (Brazil) in 2008 where SAN artery anatomical variation was investigated. The experiment involved 30 adult hearts (15 male and 15 female), RCA dominance being found.

No significant differences were found when comparing the population groups studied concerning SAN artery origin regarding country of origin since studies in which the RCA was dominant had been carried out in Switzerland, Brazil, Turkey, Senegal, Japan and England (Table 2) whilst studies in which such dominance was not so marked had been done in the USA, Brazil and India, showing that there is no apparent conditioning by source explaining such dominance.

Nevertheless, very few studies have tried to elucidate SAN irrigation in the Colombian population. Comparing the study by Ballesteros et al., (30) to this study showed a greater percentage of RCA dominance in the present work, much lower Cx dominance in this study and greater irrigation by both arteries in this study (10% compared to 3,4% in Ballesteros et al.).

The foregoing could be explained by differences in sample size, the population being studied and the research methodology used (25,27). However, these studies form a first step towards specifically understanding variables concerning the SAN artery in a sample of the Colombian population; they are useful in invasive and noninvasive diagnostic procedures and surgical and medical-legal ones.

Conclusions

This study of SAN irrigation in a sample (dissection of 60 cardiopulmonary and digestive blocks) of the Colombian population found that the SAN artery came from the RCA in 75% of the cases, 15% from the Cx artery and 10% came from co-dominant RCA and Cx artery.

SAN artery origin dominance was similar to that reported in other studies and populations. The SAN artery's anatomical distribution took a lineal route in 78.2% of the cases (81% originated in the RCA and 19% in the LCA).

RCA and LCA co-dominance regarding SAN irrigation was found in 10% of the cases. Lineal distribution of both arteries occurred in 5 cases (8.3%), terminating in a V-shaped trajectory, the vertex located in the SAN. The remaining 1.7% concerned a case of codominance in which the SAN artery came from the RCA in an inverted K-shape and a lineal branch from the LCA. It is suggested that this pilot study could be extended to all Colombian regions to determine anatomical variations' origin and distribution regarding SAN irrigation, as well as carrying out studies concerning irrigation of the rest of the cardiac conduction system in the Colombian population. It is also suggested that histological slices should be made at the SAN site together with the artery irrigating it to correlate the anatomical macroscopic part with the microscopic part.

Acknowledgements

We would like to thank the Instituto Nacional de Medicina Legal y Ciencias Forenses, Bogotá, for providing us with the material via its teaching and research agreement with the Universidad de Ciencias Aplicadas y Ambientales (UDCA) and UDCA's Faculty of Medicine for allowing us to carry out the practical phase of the research in the Universidad Nacional de Colombia's Faculty of Medicine.

Conflicts of interest

The research was carried out and the manuscript written by the authors who declare that there is no conflict of interest which could place the validity of the results presented here at risk.

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