Rare origin and course of the sinoatrial nodal artery: a cadaveric case report

doi:10.21203/rs.3.rs-2976825/v1

Download PDF

Research Article

Rare origin and course of the sinoatrial nodal artery: a cadaveric case report

https://doi.org/10.21203/rs.3.rs-2976825/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Purpose

Several previous studies reported variations in the origin and course of the sinoatrial nodal artery (SANa). In the present report, we describe a rare variation in the origin, course and relations of the SANa.

Methods

The case herein described was found during a routine dissection performed on a formalin-embalmed human adult male cadaver (82 years old).

Results

During the dissection, we identified the SANa originating from the right coronary artery (RCA) at the level of the inferior border (acute margin) of the heart and coursing upward. The initial part of this vessel is tortuous, and then it follows a straight path parallel to the RCA along the anterior surface of the right atrium. After this part, the artery curves posteriorly and to the left until it reaches the lower border of the right auricle, where it closely approaches the RCA. Finally, the artery runs posteriorly and to the right to follow a course along the medial wall of the right auricle and right atrium to reach a location close to the region of the junction of the superior vena cava and right atrium where it follows its path buried in the myocardium. We also characterized the artery radiologically through the injection of a contrast medium into the RCA and in the SANa.

Conclusion

The knowledge of the anatomical variations of the SANa is of the utmost importance for cardiologists and heart surgeons in order to better understand cardiac disease and accurately plan and execute cardiac interventions and surgical procedures.

Sinoatrial nodal artery

Human cadaveric dissection

Anatomy

Anatomical variations

Clinical relevance

The sinoatrial node is located in the wall of the right atrium in the upper part of the sulcus terminalis at the junction of the superior vena cava and the right atrium, and functions as the pacemaker of the heart [2, 4, 14]. The sinoatrial node artery (SANa), an artery whose origin, number, size and course are reported to be variable, irrigates, among other cardiac structures, the sinoatrial node. As a result, it is clinically relevant, in addition to being anatomically significant, given that it is used as a landmark for the identification of the sinoatrial node [4, 14, 17]. In a meta-analysis study published in 2016, Vikse and collaborators concluded that the SANa is more commonly a single vessel, originating from the right coronary artery (RCA), and follows more frequently a retrocaval route [17]. When the SANa emerges from the RCA, it tends to arise from its proximal segment [3, 13, 17]. Nevertheless, there are studies reporting an uncommon origin of the SANa from the more distal part of the RCA [2, 3, 5, 7]. An adequate understanding of the normal vascular anatomy and the anatomical variations is vital in several medical specialties so as to accurately perform both a broad range of diagnoses and innumerous medical procedures [7, 12–14, 17]. However, despite their importance in effective diagnosis and treatment, such variations are often overlooked in medical school curricula and clinical practice. Thus, in the current study, we describe a rare anatomical variation of the origin, course and relations of the SANa through dissection and radiological approaches.

A formalin-embalmed adult male human Portuguese cadaver (Caucasian, 82 years old) was subjected to routine dissection of the thoracic cavity at the Unit of Anatomy, Department of Biomedicine, Faculty of Medicine, University of Porto, Portugal. The cadaver derived from a body donation with informed consent, written and signed by the donor himself (Portuguese Decree-Law Nº 274/99). The complete medical history of the donor was not available. The dissection was carried out with the cadaver placed in a supine position, and all the dissection procedures were carefully performed by using appropriate dissection techniques and proper dissection tools aiming to not disturb the normal anatomy of the thoracic cavity [14]. Specifically, regarding the case report herein presented, the pericardium, the heart and the juxtacardiac parts of its great vessels, along with the coronary arteries and its branches and the cardiac veins were dissected. The length of the RCA from its origin to the origin of the SANa, and the length of the SANa from its origin to the point where it perforates the myocardium were measured by using a non-elastic wire that was placed for the purpose of following the course of the vessels. The wire was subsequently placed in a straight line on a table and measured by using a digital caliper. The same digital caliper was used to measure the diameter of the SANa at its origin and at the site where it perforates the myocardium. By using a goniometer, we also measured the angle of origin of the SANa from the RCA. With the intention of further characterizing the SANa, we clamped the RCA before and after the origin of the SANa, as well as its anterior ventricular branches, including the right marginal artery, and we injected a contrast medium (Iomeprol 300, Iomeron®) into the RCA and SANa. After this procedure, by using a standard C-arm, a right anterior oblique view chest X-ray image was taken.

During the dissection of the initial part of the RCA, we tried to find the SANa bearing in mind that it more commonly arises from this part of the RCA. In spite of that, we did not detect the SANa in this location and we continued with the dissection of the RCA. At the level of the inferior border (acute margin) of the heart, the described RCA follows an unusual and almost horizontal trajectory to the right before curving around the inferior border of the heart into the inferior part of the atrioventricular (coronary) sulcus, where it continues towards the cardiac crux. Originating from this almost horizontal segment of the RCA we identified a large caliber branch arising from its anterosuperior aspect and running upward (Fig. 1a). Afterwards, we dissected this branch and pursued its course. Firstly, the artery follows a tortuous path and then it runs approximately parallel to the coronary sulcus and RCA along the anterior surface of the right atrium. More superiorly, it bends posteriorly and to the left until it reaches the lower border of the right auricle. In this part of its trajectory, the artery is located close to and inferiorly and to the right of the RCA. After that, the vessel continues posteriorly and to the right to follow a route along the medial surface of the right auricle and right atrium to reach a point in the vicinity of the region of the junction of the right atrium and superior vena cava where it enters the myocardium of the right atrium (Fig. 1b and 1c), thus appearing to evidently be the SANa. The course, relations and distribution are also suggestive in the X-ray image (Fig. 2), corroborating the macroscopic dissection’s assessment. Moreover, in the segment of the RCA between its emergence from the ascending aorta and inferior border of the heart, we did not identify any anterior atrial branch. However, in the extent of SANa that we dissected, we found three branches that reach the right atrium. The first one, of large caliber, originates near the beginning of the SANa, and the other two, of small caliber, originate from the SANa when it is located in relation to the medial wall of the right atrium (Fig. 1).

In regard to the morphometric data, we found that the length of the RCA from its origin in the ascending aorta to the origin of the SANa was 71.23 mm. The length of the SANa from its origin to the site where it perforates the myocardium was 100.14 mm. The diameter of the SANa at its origin and where it enters the myocardium was 2.35 mm and 1.90 mm, respectively. The angle of origin of the SANa from its parent trunk was an obtuse angle (95º).

Considering the complex embryology of the coronary arteries, it is expected that changes in development can lead to coronary artery anomalies and variations [6, 16]. Here, we presented a rare case of variation in the origin, course and relations of the SANa. Although we did not perform a microdissection or a histological study, the route and distribution seen macroscopically and through the X-ray image enabled us to conclude that it is in fact the SANa. In our case, the SANa is the sole anterior atrial branch of the segment of the RCA between its emergence from the ascending aorta and the inferior border of the heart.

Regarding the origin the SANa, in our study, we found an uncommon origin from the RCA at the level of the inferior border of the heart. We observe that the length of the RCA measured from the aorta to the origin of the SANa was 71.23 mm. In a meta-analysis, Vikse and collaborators analyzed 18 studies in which the pooled mean distance between the origin of the SANa and the ostia of the RCA was 16.306 mm [17]. Therefore, contrarily to what happens in the majority of cases, in which the SANa originates from the initial part of the RCA, the artery that we detail in the present study has a considerable distant origin from the emergence of the RCA from the ascending aorta. Similarly, there are studies reporting sinoatrial nodal arteries arising from the RCA at a maximal distance of 62 mm [9] and 84.3 mm [1] from the RCA ostium. Effectively, in our case, the SANa originates just before the RCA curves around the inferior border of the heart into the inferior part of the atrioventricular sulcus. There are studies that report cases in which the SANa arises at or near the inferior border of the heart [3, 5]. In both studies just cited, and differently from the path followed by the SANa currently described, it is reported that these vessels, in their trajectory, passed along the lateral wall of the right atrium [3, 5]. The disclosed occurrence of the origin of SANa at this level varies widely between studies. Indeed, in one of the aforementioned studies, it was observed in 1 of 309 (0.32%) patients studied [5], and in the other it was found in 6 of 40 (15%) studied hearts [3]. Notably, the SANa detailed by Kyriakidis and collaborators originating near the origin of the acute marginal artery was one of the two arteries of sinus node out of 309 that showed atheroma [5]. Similarly, Ozturk and colleagues discovered an atherosclerotic plaque in the SANa in 3 cases out of 251 [9]. In this context, it is important to emphasize that it was recently observed in a study carried out on 59 adult hearts (average age of subjects, 70.6 ± 14.5 years) that, independently of the SANa origin, calcification scarcely occurred in this artery in old age [15].

In relation to the length of the SANa, we verified that from its origin until the site where it perforates the myocardium the SANa length was 100.14 mm. In the literature, we found references to a wide range of SANa length values. The obtained measure falls within the scope of values detailed in some studies about the length of the SANa originating from RCA. For instance, Ortale and collaborators analyzed 25 human hearts in which a single SANa that originated from the RCA had a reported length of between 41.6 mm and 105.0 mm [8], and Nerantzis and collaborators disclosed a length of 98 mm from a SNAa arising from the RCA at mid-distance between the origin of the right marginal artery and the posterior interventricular artery [7].

Concerning the diameter of the SANa, we measured 2.35 mm and 1.90 mm at its origin and at the point where it enters the myocardium, respectively. The diameter of the SANa described in our study decreases slightly from its origin until it enters the myocardium. This fact is explained by taking into account that in its course it was only possible to identify a large caliber branch next to its beginning, and then two smaller caliber branches in the proximity of the location where it enters the myocardium. In the aforementioned meta-analysis, Vikse and collaborators, by analyzing seven studies, showed that the pooled mean diameter of the SANa originating from the RCA was 1.349 mm at its origin [17]. Hence, the diameter of the SANa we studied is, at its origin, considerably superior to these previously reported mean values. Nonetheless, there are studies in the literature in which the authors described a SANa arising from the RCA with a diameter higher than those we registered. For instance, there are reports of 2.70 mm [1] and 3 mm [11].

Regarding the angle of origin of the SANa from the RCA, we observed an obtuse angle (95º). It was previously verified that in most of the hearths (48%) the SANa originates from the parent trunk at an obtuse angle [10]. The angle of origin of SANa is clearly an anatomic and clinically relevant issue concerning the blood circulation in the arteries since the risk of thrombotic obstruction increases with the acuteness of its branching pattern from its parent trunk [10].

In the present study, we describe a rare variation of the SANa found during a routine cadaveric dissection. The knowledge of the anatomical variations of the SANa, even if it is one of its rarest variations, is valuable for anatomists and of great clinical significance for cardiac surgeons and interventional cardiologists in carrying out diagnoses as well as in planning and executing invasive cardiac procedures and surgical interventions.

Funding No funding was received for conducting this study.

Competing interests The authors have no competing interests to declare that are relevant to the content of this article.

Conflict of interest The authors declare that they have no conflict of interest.

Ethical approval All procedures performed in the cadaver were in accordance with the Portuguese Decree-Law Nº 274/99.

Data availability Not applicable.

Author contributions MD Madeira: Dissection, Data collection and analysis, Manuscript writing/editing. FF Pinto: Dissection, Data collection and analysis, Manuscript writing/editing. PA Pereira: Dissection, Data collection and analysis, Manuscript writing/editing. All authors have read and approved the final manuscript.

Statements and Declarations

Competing interests: The authors have no competing interests to declare that are relevant to the content of this article.

Acknowledgements: The authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase mankind's overall knowledge that can then improve patient care. Therefore, these donors and their families deserve our highest gratitude.

The authors also wish to thank the Unit of Anatomy Technicians Filipe Silva and Hélder Bastos for their technical assistance, as well as the Radiological Technicians Paula Cardoso and Leila Pereira for their technical assistance in the radiological study herein displayed.

Cezlan T, Senturk S, Karcaaltıncaba M, Bilici A (2012) Multidetector CT imaging of arterial supply to sinoatrial and atrioventricular nodes. Surg Radiol Anat 34:357–365. https://doi.org/10.1007/s00276-011-0902-y
Futami C, Tanuma K, Tanuma Y, Saito T (2003) The arterial blood supply of the conducting system in normal human hearts. Surg Radiol Anat 25:42–49. https://doi.org/10.1007/s00276-002-0085-7
Hutchinson MC (1978) A study of the artrial arteries in man. J Anat 125(Pt 1):39–54.
Kawashima T, Sasaki H (2003) The morphological significance of the human sinuatrial nodal branch (artery). Heart Vessels 18:213–219. https://doi.org/10.1007/s00380-003-0710-3
Kyriakidis M, Vyssoulis G, Barbetseas J, Toutouzas P (1988) A clinical angiographic study of the arterial blood supply to the sinus node. Chest 94:1054–1057. https://doi.org/10.1378/chest.94.5.1054
Loukas M, Groat C, Khangura R, Owens DG, Anderson RH (2009). The normal and abnormal anatomy of the coronary arteries. Clin Anat 22:114–128. https://doi.org/10.1002/ca.20761
Nerantzis CE, Koulouris S, Pastromas S (2011) Sinus node artery originating from the posterior part of the right coronary artery. Surg Radiol Anat 33:373–375. https://doi.org/10.1007/s00276-010-0717-2
Ortale JR, Paganoti CF, Marchiori GF (2006) Anatomical variations in the human sinuatrial nodal artery. Clinics 61:551–558. https://doi.org/10.1590/S1807-59322006000600011
Ozturk E, Saglam M, Bozlar U, Kemal Sivrioglu A, Karaman B, Onat L, Cinar Basekim C (2011) Arterial supply of the sinoatrial node: a CT coronary angiographic study. Int J Cardiovasc Imaging 27:619–627. https://doi.org/10.1007/s10554-010-9705-1
Pare V, Kulkarni R, Nayak SG (2017) Interesting observations on sinoatrial nodal artery: a clinical perspective. Int J Anat Res 5:3372–3378. DOI:10.16965/ijar.2016.482
Pejković B, Krajnc I, Anderhuber F, Kosutić D (2008) Anatomical aspects of the arterial blood supply to the sinoatrial and atrioventricular nodes of the human heart. J Int Med Res 36:691–698. https://doi.org/10.1177/14732300080360041
Pinho AR, Pereira PA, Leite MJ, Santos CC, Vaz RP, Madeira MD (2022) The Surgical Vascular Anatomy of the Lower Lumbar Arteries and Its Implications in Minimally Invasive Spine Surgery: A Cadaveric Study. Int J Spine Surg 16:631–637. https://doi.org/10.14444/8298
Sow ML, Ndoye JM, Lô EA (1996) The artery of the sinuatrial node: anatomic considerations based on 45 injection-dissections of the heart. Surg Radiol Anat 18:103–109. https://doi.org/10.1007/BF01795227
Standring S, Editor-in-Chief (2021) Gray’s Anatomy. The Anatomical Basis of Clinical Practice. 42nd Edition, Elsevier.
TohnoY, TohnoS, Quiggins R, Minami T, Mahakkanukrauh P (2018) Scarce occurrence of calcification in human sinoatrial nodal arteries in old age. Biol Trace Elem Res 184:24–32. https://doi.org/10.1007/s12011-017-1173-1
Tomanek R, Angelini P (2019) Embryology of coronary arteries and anatomy/pathophysiology of coronary anomalies. A comprehensive update. Int J Cardiol 281:28–34. https://doi.org/10.1016/j.ijcard.2018.11.135
Vikse J, Henry BM, Roy J, Ramakrishnan PK, Hsieh WC, Walocha JA, Tomaszewski KA (2016) Anatomical Variations in the Sinoatrial Nodal Artery: A Meta-Analysis and Clinical Considerations. PLoS One 11(2):e0148331. https://doi.org/10.1371/journal.pone.0148331. Erratum in: PLoS One 11(3): e0150051. https://doi.org/10.1371/journal.pone.0150051

No competing interests reported.

Download PDF

Version 1

posted

You are reading this latest preprint version

Rare origin and course of the sinoatrial nodal artery: a cadaveric case report

Status:

Version 1

Abstract

Purpose

Methods

Results

Conclusion

Figures

Introduction

Methods

Results

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1