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Published online before print November 16, 2007, 10.1148/radiol.2461070030
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(Radiology 2008;246:99-107.)
© RSNA, 2007

Cardiac Imaging

Arterial Supply to Sinuatrial and Atrioventricular Nodes: Imaging with Multidetector CT1

Farhood Saremi, MD, Amir Abolhoda, MD, Oganes Ashikyan, MD, Jeffrey C. Milliken, MD, Jagat Narula, MD, Swaminatha V. Gurudevan, MD, Khushboo Kaushal, BS, and Aidan Raney, BA

1 From the Departments of Radiological Sciences (F.S., O.A., K.K., A.R.), Cardiology (J.N., S.V.G.), and Cardiothoracic Surgery (A.A., J.C.M.), University of California, Irvine, University of California Medical Center, 101 The City Drive, Route 140, Orange, CA 92868-3298. Received January 8, 2007; revision requested February 28; revision received March 13; accepted April 20; final version accepted June 11. Address correspondence to F.S. (e-mail: fsaremi{at}uci.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Purpose: To retrospectively evaluate the depiction of anatomic characteristics of the arterial supply to the sinuatrial node (SAN) and the atrioventricular node (AVN) with 64-section computed tomography (CT).

Materials and Methods: The institutional review board approved this HIPAA-compliant study; informed consent was not required. Anatomic origin, number, course, and variants of the arteries to the SAN and AVN were examined with coronary multidetector CT in 102 patients (55 men, 47 women; mean age, 57 years ± 13 [standard deviation]). Known accessory blood supplies to the AVN, including left and right Kugel anastomotic arteries, were investigated. Possible extension of the first septal perforating artery to the AVN was evaluated. Univariate and bivariate statistical data were reported. Means ± standard deviations, 95% confidence intervals, and percentages were calculated.

Results: A single sinuatrial nodal artery originated from the proximal 40 mm of the right coronary artery (RCA) in 67 and from the proximal 35 mm of the left circumflex (LCX) artery in 28 patients. A dual blood supply to the SAN was seen in six patients. The sinuatrial nodal artery was not visualized in one patient. An S-shaped variant was seen in 18% of left sinuatrial nodal arteries and invariably traveled posteriorly in the sulcus between the left superior pulmonary vein and left atrial appendage. The sinuatrial nodal artery approached the nodal tissue by one of three routes—retrocaval (47.5%), precaval (42.6%), or pericaval (9.9%). The AVN was supplied by the RCA in 89 patients, the LCX artery in 11 patients, and by both arteries in two patients. Two left and six right Kugel anastomotic arteries were detected as supplying the AVN area. The first septal perforating artery had no detectable connection to the AVN.

Conclusion: The arterial blood supply to the SAN and the AVN is variable and can be imaged with multidectector CT.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/2461070030/DC1

© RSNA, 2007


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
An active area of clinical research has been multidetector computed tomographic (CT) coronary artery imaging (1–4). By providing 0.5-mm isotropic voxels with a rotation time of less than 400 msec (5–7), use of 64-section CT scanners results in further improvement in image quality for assessment of epicardial coronary arteries and their smaller branch vessels. In addition, these images illustrate the spatial relationships of these vessels to other cardiac structures.

To our knowledge, there has been no systematic investigation of the origin and course of the arterial supply of the sinuatrial node (SAN) and the atrioventricular node (AVN) by using multidetector CT technology. This knowledge may not only enrich our understanding of the spatial relationships pertaining to cardiac vascular anatomy but also could potentially influence preprocedural planning in a number of catheter-based or open surgical procedures performed near these important structures. Thus, the purpose of our study was to retrospectively evaluate depiction of anatomic characteristics of the arterial supply to the SAN and the AVN with 64-section CT.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
We conducted a retrospective analysis of electrocardiographically gated multidetector CT coronary artery examinations performed with a 64-section scanner (Aquilion; Toshiba, Tustin, Calif) within 2 months (January and February 2006) in 110 consecutive patients. Patients were either self-referred (n = 67) or referred by a physician for suspicion of having coronary artery disease. Eight patients were excluded because of severe artifacts created by the presence of surgical clips (n = 5), prosthetic heart valves (n = 1), pacemaker leads (n = 1), and atrial fibrillation (n = 1). The remaining 102 patients (55 men, 47 women; mean age, 57 years ± 13 [standard deviation]; age range, 31–84 years) were included in this study. The study was conducted with the approval of the institutional review board at the University of California, Irvine, and was compliant with Health Insurance Portability and Accountability Act regulations. Informed consent was not required for this retrospective analysis.

Patient Preparation
Vital signs and an electrocardiogram were obtained in all patients when they arrived at the imaging suite. Oral and intravenous metoprolol (Lopressor; Novartis Pharmaceuticals, Suffern, New York) were used as needed to achieve a target heart rate of less than 65 beats per minute. Sublingual nitroglycerin (tablet, 0.4–0.8 mg) was administered 1 minute prior to image acquisition, unless patients had a contraindication to nitroglycerin. Mean heart rate before data acquisition was 61 beats per minute ± 5 (range, 53–75 beats per minute).

Scanning Protocol and Image Reconstruction
The scanner used in this study was equipped with 64 parallel detector rows, with an individual detector width of 0.5 mm. Contrast enhancement was achieved by using 65 mL of iohexol (Omnipaque 350; Amersham Health, Cork, Ireland) injected at a rate of 4–5 mL/sec, followed by an injection of 50 mL of saline at a rate of 5 mL/sec through an 18-gauge catheter into an antecubital vein to allow washout of contrast material from the right side of the heart and superior vena cava (SVC). The scan parameters were as follows: collimation, 64 x 0.5 mm; table feed per rotation, 7.2 mm; gantry rotation time, 400 msec; tube voltage, 120 kVp; and tube current, 400 mA. Start delay was defined with bolus tracking in the descending aorta at the tracheal bifurcation level, and scan start was automatically initiated 4 seconds after reaching the threshold of 180 HU. Retrospective electrocardiographically gated volumetric data sets were acquired during a single breath hold. Mean scan time was 9.5 seconds ± 1.4 (range, 8–13 seconds), and total time for the examination was less than 15 minutes (median, 12 minutes; range, 8–14 minutes).

Depending on the heart rate throughout the examination, transverse sections were reconstructed synchronized to the electrocardiogram by using a nonsegmented (≤65 beats per minute) or segmented (>65 beats per minute) image reconstruction algorithm. When necessary, R-wave indicators were manually repositioned to improve the quality of synchronization. Diastolic transverse images were reconstructed by using a relative-delay strategy at 70%, 75%, and 80% of the R-R interval. In case of persistent artifacts related to coronary motion at the atrioventricular junction, a second reconstruction approach was performed, and systolic images were reconstructed by using an absolute-delay strategy with a 350–400-msec delay time after the previous R wave. Data sets reconstructed during the diastolic phase were used in all patients. In addition to diastolic data, systolic data were used in nine patients. Transverse sections with a thickness of 0.5 mm (increment, 0.3 mm) and a cardiac CT angiographic algorithm were used for the evaluation of coronary vessels and conduction system branches. The data set least affected by cardiac motion was transferred to an off-line three-dimensional workstation (Vitrea; Vital Images, Minnetonka, Minn) for further analysis.

CT Data Analysis
Multiplanar reformations of the transverse images were rendered and evaluated in consensus by a radiologist (F.S.) and a cardiologist (S.V.G.) with 15 and 2 years of experience in CT interpretation, respectively. Depending on the individual coronary anatomy and image quality, different visualization techniques—such as multiplanar reformation, maximum intensity projection, and three-dimensional reconstruction with tissue sculpturing—were used. Overall image quality was subjectively evaluated and classified as good, adequate, or poor; classification was primarily based on common image-degrading artifacts related to motion, background noise, or large calcifications.

The degree of visualization of each vessel, including the sinuatrial nodal branch of the right coronary artery (RCA) (hereafter, sinuatrial nodal artery), the atrioventricular nodal branch (hereafter, atrioventricular nodal artery), and the first septal perforating artery, was evaluated in different views. The sinuatrial nodal artery was divided into two segments: proximal and distal. Factors that might result in less than excellent vessel visualization include noise, calcification, poor vessel enhancement, streak artifacts related to a contrast material–enhanced SVC or cardiac chamber, and motion or pulsation artifacts. A subjective five-point scale (1 to 5; nonvisible to excellent visualization, respectively) was used to classify the degree of visualization.

Coronary vessels were studied to find the dominant vessel. Images were analyzed for the origin, number, anatomic course, and anatomic variants of the arteries to the SAN and AVN regions. The distance between the ostium of the RCA or the left circumflex (LCX) artery and the origin of the right or left sinuatrial nodal artery was measured. The mode of termination of the sinuatrial nodal artery in relation to the SVC was classified as retrocaval, precaval, or pericaval. By using three-dimensional images and with respect to the mode of termination (retrocaval vs precaval), the spatial relation of the sinuatrial nodal artery to the superior border of the interatrial septum was visually estimated and recorded as close versus remote. The nodal arteries were evaluated for the presence and degree of branching to the right or left atrial walls. Each patient was evaluated for the presence of additional anatomic findings, including accessory branches or dual blood supply. The walls of sinuatrial nodal arteries and atrioventricular nodal arteries were assessed for the presence of calcified and noncalcified atherosclerotic plaques. By using four-chamber views, the closest distance of the atrioventricular nodal artery to the endocardial surface of the coronary sinus ostium at the base of the Koch triangle was measured. In patients with an S-shaped posterior sinuatrial nodal artery, the anatomic course of the vessel was assessed, and its closest distance to the left atrial wall in the groove between the ostium of the left superior pulmonary vein and left atrial appendage was measured.

Alternative sources of blood supply to the AVN, such as left and right atrial periaortic anastomotic branches between the LCX artery and RCA (hereafter, Kugel anastomotic artery; right Kugel anastomotic artery is also known as right superior descending artery), including their origin, location, and anatomic course, were identified. The origin and length of the first septal perforating artery were determined, and images were reviewed for possible extension to the AVN area. Previously described nomenclature (8–29) was used (Table E1, http://radiology.rsnajnls.org/cgi/content/full/2461070030/DC1).

Statistical Analysis
Statistical analysis was performed by using software (SAS, version 9.1.3; SAS Institute, Cary, NC). Univariate statistics for all continuous data were reported by using mean ± standard error. We also reported 95% confidence interval estimates of the true means and percentages. We reported statistical results from several bivariate comparisons. For all cases in which a statistical test was conducted, a P value of less than .05 was considered to indicate a significant difference.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Image Quality and Degree of Vessel Visualization
Overall image quality was classified as good in 88.2%, adequate in 6.8%, and poor in 4.9% of the studies. Factors resulting in poor image quality in most studies were motion or pulsation artifacts or low contrast-to-noise ratios.

The mean degree of visualization for conduction system vessels was 4.3 ± 0.6 at the proximal sinuatrial nodal artery arising from the RCA, 4.3 ± 0.8 at the proximal sinuatrial nodal artery arising from the LCX artery, 3.5 ± 0.8 at the distal sinuatrial nodal artery near the SVC, 4.3 ± 0.6 at the atrioventricular nodal artery, and 3.7 ± 1.0 at the first septal perforating artery. We found that transverse images were the optimal orientation for visualization of the anatomic course of sinuatrial nodal arteries. Atrioventricular nodal arteries were best seen on short-axis views at the level of the cardiac crux. The first septal perforating artery was best seen on short-axis images at the level of the pulmonary outflow tract.

Sinuatrial Nodal Artery
Among the 102 hearts studied, 89 were right dominant (giving rise to a posterior descending artery), 11 were left dominant, and two were balanced. A single sinuatrial nodal artery arose from the RCA in 67 (65.7%) cases and from the LCX artery in 28 (27.4%) cases (Table E2, http://radiology.rsnajnls.org/cgi/content/full/2461070030/DC1). A dual blood supply to the SAN was seen in six (5.9%) cases: one supply from the RCA and the other supply from the LCX artery. In one patient, the sinuatrial nodal artery was not visualized. Of 28 SAN arteries arising from the LCX artery, 27 were right dominant and only one was left dominant. Of 67 sinuatrial nodal arteries arising from the RCA, 10 (15%) were left dominant and 57 (85%) were right dominant. Regardless of the dominance, the side of origin of the sinuatrial nodal artery that was seen most frequently was the right side. The relationship between the side of origin of the sinuatrial nodal artery and the patient's sex was not significant ({chi}2 = 0.32, P = .56).

The distance between the RCA ostium and the origin of the right sinuatrial nodal artery ranged from 0 to 40 mm (mean, 16 mm ± 7). The sinuatrial nodal artery originated from the RCA ostium in two patients. The distance between the LCX artery ostium and the origin of the left sinuatrial nodal artery ranged from 2 to 35 mm (mean, 12 mm ± 6). The left sinuatrial nodal artery typically traveled along the transverse sinus toward the SVC. The terminal sinuatrial nodal arteries approached the SAN anterior to the SVC (precaval) in 43 (42.6%) patients, posterior to the SVC (retrocaval) in 48 (47.5%) patients, and through multiple branches surrounding the SVC (pericaval) in 10 (9.9%) patients (Figs 1–3). The latter mode of termination was more common in patients with a dual blood supply to the SAN (three of six patients). Although the retrocaval mode of termination was the most common pattern, there was no significant difference between it and the precaval mode of termination ({chi}2 = 0.27, P = .6). The terminal sinuatrial nodal artery typically traveled close to the superior border of the interatrial septum when it was retrocaval (Fig 2) versus when it was precaval (Fig 3).


Figure 1A
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  		Figure 1a: Transverse CT images show modes of termination of sinuatrial nodal artery (arrows) relative to SVC: (a) retrocaval (47.5%), (b) precaval (42.6%), and (c) pericaval (9.9%). AAo = ascending aorta, LA = left atrium.

 

Figure 1B
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  		Figure 1b: Transverse CT images show modes of termination of sinuatrial nodal artery (arrows) relative to SVC: (a) retrocaval (47.5%), (b) precaval (42.6%), and (c) pericaval (9.9%). AAo = ascending aorta, LA = left atrium.

 

Figure 1C
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  		Figure 1c: Transverse CT images show modes of termination of sinuatrial nodal artery (arrows) relative to SVC: (a) retrocaval (47.5%), (b) precaval (42.6%), and (c) pericaval (9.9%). AAo = ascending aorta, LA = left atrium.

 

Figure 2
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  		Figure 2: Left: Transverse images of coronary CT angiographic data. Right: Superior views of sculptured three-dimensional reconstruction of heart. Red arrows point to retrocaval sinuatrial nodal arteries arising from RCA (top) and from LCX artery (bottom). Approximate incision line in superior septal approach for mitral valve surgery is shown (green arrows). In retrocaval variant, artery is very close to interatrial groove and a typical surgical incision would cut through the sinuatrial nodal artery where it passes the interatrial groove toward the posterior aspect of the SVC. AAo = ascending aorta, LA = left atrium, RAA = right atrial appendage.

 

Figure 3A
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  		Figure 3a: (a) Anterior and (b) right anterior oblique (RAO) views of sculptured three-dimensional reconstruction of heart and related transverse images (insets) demonstrate precaval sinuatrial nodal artery arising from (a) LCX artery (white arrows) and (b) RCA (black arrows). Approximate incision line in superior transseptal approach for mitral valve surgery (green arrows) extends from right atrium (RA) toward dome of left atrium (LA) superior to interatrial septum (IAS) (red arrows). This approach is below the level of the course of the sinuatrial nodal artery (SANa) in precaval variant, in which the artery terminates anterior to the SVC. In this case, risk of injury to vessel is negligible if the incision is made with caution. AAo = ascending aorta, LV = left ventricle, RAA = right atrial appendage, RV = right ventricle.

 

Figure 3B
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  		Figure 3b: (a) Anterior and (b) right anterior oblique (RAO) views of sculptured three-dimensional reconstruction of heart and related transverse images (insets) demonstrate precaval sinuatrial nodal artery arising from (a) LCX artery (white arrows) and (b) RCA (black arrows). Approximate incision line in superior transseptal approach for mitral valve surgery (green arrows) extends from right atrium (RA) toward dome of left atrium (LA) superior to interatrial septum (IAS) (red arrows). This approach is below the level of the course of the sinuatrial nodal artery (SANa) in precaval variant, in which the artery terminates anterior to the SVC. In this case, risk of injury to vessel is negligible if the incision is made with caution. AAo = ascending aorta, LV = left ventricle, RAA = right atrial appendage, RV = right ventricle.

 
Small atrial branches were commonly seen supplying the left atrium, the anterior part of the interatrial septum, and the right atrium. These small atrial branches were seen in 55% of right sinuatrial nodal arteries and in 57% of left sinuatrial nodal arteries. In one patient with extensive coronary artery disease in the major coronary arteries, the sinuatrial nodal artery contained a relatively large calcified plaque located 10 mm from its origin.

S-Shaped Posterior Sinuatrial Nodal Artery
We identified a long sinuatrial nodal artery with an S-shaped course in six patients (5.9% of all arteries and 18% of the sinuatrial nodal arteries arising from the LCX artery). This artery appeared larger than the normal sinuatrial nodal artery and originated in the proximal part of the LCX artery (distance range, 6–35 mm). This artery always followed the same route, coursing posteriorly in a groove at the junction between the mouth of the left atrial appendage and the orifice of the the left superior pulmonary vein (Fig 4). In this groove, the artery was in close proximity to the left superior pulmonary vein ostium, and the distance varied from 1 to 3 mm. It then followed the course observed in other left sinuatrial nodal arteries, traveling along the tranverse sinus toward the SVC.


Figure 4A
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  		Figure 4a: (a) Left superior three-dimensional and (b) transverse maximum intensity projection images from CT show S-shaped sinuatrial nodal artery arising from proximal LCX artery, running posteriorly between left atrial appendage (LAA) and left superior pulmonary vein (LSPV) (arrow). In this location, it is very close to myocardial wall and may be damaged during radiofrequency ablation or surgical maze procedure of left atrium (LA). Artery approaches SAN through transverse sinus and anterior to SVC. AAo = ascending aorta, LAD = left anterior descending artery, RAA = right atrial appendage. Orientation: A = anterior, L = left, P = posterior, R = right.

 

Figure 4B
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  		Figure 4b: (a) Left superior three-dimensional and (b) transverse maximum intensity projection images from CT show S-shaped sinuatrial nodal artery arising from proximal LCX artery, running posteriorly between left atrial appendage (LAA) and left superior pulmonary vein (LSPV) (arrow). In this location, it is very close to myocardial wall and may be damaged during radiofrequency ablation or surgical maze procedure of left atrium (LA). Artery approaches SAN through transverse sinus and anterior to SVC. AAo = ascending aorta, LAD = left anterior descending artery, RAA = right atrial appendage. Orientation: A = anterior, L = left, P = posterior, R = right.

 
Atrioventricular Nodal Artery
The atrioventricular nodal artery arose from the distal RCA in 89 (87.2%) patients and from the distal LCX artery in 11 (10.8%) patients (Fig 5). A dual supply (codominant coronary system) originating from both the RCA and the LCX artery was observed in two (2.0%) patients. An accessory atrioventricular nodal artery arising from the distal RCA was seen in one patient, and one patient had an accessory artery that branched from an S-shaped left sinuatrial nodal artery in the transverse sinus at the level of the interatrial septum. In one patient, the atrioventricular nodal artery continued as a large atrial branch that supplied the posterior wall of the left atrium. The relationship between the side of origin of the atrioventricular nodal artery and the sex of the patient was not significant ({chi}2 = 1.37, P = .24). The distance of the closest point of the atrioventricular nodal artery to the endocardial surface of the coronary sinus ostium at the base of the Koch triangle ranged from 1 to 6 mm (mean, 2 mm ± 1) (Fig 6). A partially calcified atherosclerotic plaque was seen at the middle portion of one atrioventricular nodal artery (as part of diffuse disease involving other coronary arteries).


Figure 5A
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  		Figure 5a: Short-axis views of coronary CT angiographic data. Arrow = right atrioventricular nodal artery arising from (a) RCA and (b) LCX artery. AAo = ascending aorta, RA = right atrium.

 

Figure 5B
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  		Figure 5b: Short-axis views of coronary CT angiographic data. Arrow = right atrioventricular nodal artery arising from (a) RCA and (b) LCX artery. AAo = ascending aorta, RA = right atrium.

 

Figure 6
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  		Figure 6: CT images of relationship between atrioventricular nodal artery and base of Koch triangle (coronary sinus [CS] ostium). A, Endocardial view of right atrioventricular junction shows anatomic boundaries of Koch triangle. Triangle is oriented with central fibrous body (CFB) at apex and is demarcated by Todaro tendon posteriorly (white arrows), hinge line of septal tricuspid valve (yellow arrows) anteriorly, and coronary sinus at base. Septal isthmus (green bracket) is located at triangle base, connecting tricuspid annulus to coronary sinus ostium. B, C, Four-chamber views at level of coronary sinus ostium in two patients. Black arrows indicate atrioventricular nodal artery at level of septal isthmus. Note variable distances of atrioventricular nodal artery to surface of endocardium. There is risk of arterial coagulation during ablation procedures when artery is in close proximity to septal wall, as in B. IVC = inferior vena cava, PFO = patent foramen ovale, RV = right ventricle. Orientation: A = anterior, I = inferior, P = posterior, S = superior.

 
Left Kugel Anastomotic Artery
In two patients, left Kugel anastomotic arteries were seen originating from the proximal 10 mm of the LCX artery (Fig 7). The arteries traveled through the epicardial fat in the atrioventricular groove, coursing along the side of the aorta and then behind it in close proximity to the noncoronary cusp before entering the interatrial septum near the AVN to meet the atrioventricular nodal artery.


Figure 7A
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  		Figure 7a: (a) Schematic representation of posterior view at CT of heart demonstrates atrial vessel supply to AVN, including right (Rt. Kugel's) and left (Lt. Kugel's) Kugel anastomotic arteries and atrioventricular nodal artery (AVNa). (b) Tilted short-axis and (c) four-chamber views show accessory branches to AVN area. In b, left Kugel anastomotic artery arising from proximal LCX artery (black arrows) is evident. In c, right Kugel anastomotic artery is shown originating from proximal RCA (black arrows). Kugel anastomotic arteries travel through epicardial fat in the atrioventricular groove, extending along the side of aorta and then behind it, and reach the interatrial septum near its junction with the interventricular septum. AAo = ascending aorta, LA = left atrium, LV = left ventricle, MV = mitral valve, RA = right atrium, RV = right ventricle, TR = tricuspid valve.

 

Figure 7B
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  		Figure 7b: (a) Schematic representation of posterior view at CT of heart demonstrates atrial vessel supply to AVN, including right (Rt. Kugel's) and left (Lt. Kugel's) Kugel anastomotic arteries and atrioventricular nodal artery (AVNa). (b) Tilted short-axis and (c) four-chamber views show accessory branches to AVN area. In b, left Kugel anastomotic artery arising from proximal LCX artery (black arrows) is evident. In c, right Kugel anastomotic artery is shown originating from proximal RCA (black arrows). Kugel anastomotic arteries travel through epicardial fat in the atrioventricular groove, extending along the side of aorta and then behind it, and reach the interatrial septum near its junction with the interventricular septum. AAo = ascending aorta, LA = left atrium, LV = left ventricle, MV = mitral valve, RA = right atrium, RV = right ventricle, TR = tricuspid valve.

 

Figure 7C
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  		Figure 7c: (a) Schematic representation of posterior view at CT of heart demonstrates atrial vessel supply to AVN, including right (Rt. Kugel's) and left (Lt. Kugel's) Kugel anastomotic arteries and atrioventricular nodal artery (AVNa). (b) Tilted short-axis and (c) four-chamber views show accessory branches to AVN area. In b, left Kugel anastomotic artery arising from proximal LCX artery (black arrows) is evident. In c, right Kugel anastomotic artery is shown originating from proximal RCA (black arrows). Kugel anastomotic arteries travel through epicardial fat in the atrioventricular groove, extending along the side of aorta and then behind it, and reach the interatrial septum near its junction with the interventricular septum. AAo = ascending aorta, LA = left atrium, LV = left ventricle, MV = mitral valve, RA = right atrium, RV = right ventricle, TR = tricuspid valve.

 
Right Kugel Anastomotic Artery
A right Kugel anastomotic artery was identified in six (5.9%) patients. All patients had a single vessel that originated from one of three locations—the proximal 15 mm of the RCA in three patients, the right sinuatrial nodal artery in two patients, and from a conus artery in one patient. In all patients, these arteries penetrated the epicardial fat in the atrioventricular groove, coursing along the right side of the aortic root and then behind it to meet the interatrial septum near its junction with the interventricular septum at the base of the heart (Fig 7).

First Septal Perforating Artery
First septal perforating arteries invariably arose from the proximal left anterior descending artery and branched perpendicularly into the right side of the basal interventricular septum. They varied in length from 22 to 50 mm (mean, 34.4 mm ± 6; 95% confidence interval: 33.2, 35.6 mm). We found no detectable branches to the anatomic zone near the termination of the atrioventricular nodal artery, where the atrioventricular nodal tissue is presumably situated.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 
Anatomic descriptions of the blood supply of the cardiac conduction system, specifically the SAN and the AVN, have been reported in several published articles in the literature (10–19). These descriptions have been based solely on detailed cadaveric dissections of the human heart and/or angiographic studies. To our knowledge, our study is the first to use cardiac multidetector CT to describe the anatomic origin and course of the arterial blood supply to the SAN and AVN.

Our data compare well with the published cadaveric and angiographic findings (13,14,17,30–33) (Table E3, http://radiology.rsnajnls.org/cgi/content/full/2461070030/DC1). In the study conducted by Busquet et al (14), variability was found in the course of the sinuatrial nodal artery relative to the cavoatrial junction—precaval (58%), retrocaval (36%), and encircling (6%). We observed in our study that the terminal sinuatrial nodal arteries approached the SAN posterior to the SVC (retrocaval) in 48 (47.5%) patients and through multiple branches surrounding the SVC (pericaval) in nine (9.9%) patients. In a study by Berdajs et al (11), the authors examined 50 human hearts from cadavers without previous pathologic alterations and found that the sinuatrial nodal artery crossed the superior posterior border of the interatrial septum in 54% of the hearts. We observed in our study that the terminal sinuatrial nodal artery traveled closer to the superior aspect of the interatrial septum in selected groups. According to our anatomic findings, all retrocaval and pericaval sinuatrial nodal arteries (especially those arising from the LCX artery) are prone to surgical trauma during superior transseptal incisions (34–36). These injuries can be avoided by employing alternative left atrial incisions (eg, the posterior interatrial groove approach).

In our study, we found a variant of the left sinuatrial nodal artery with an S-shaped course arising from the proximal LCX artery. McAlpine (8) provided a detailed description of the posterior sinuatrial nodal artery. Nerantzis and Avgoustakis (15) described it as a long S-shaped artery originating in the posterolateral part of the LCX artery below or behind the left auricle. In their coronary artery study of 300 human hearts, this anatomy was observed in 21% of the cases in which the sinuatrial nodal artery arose from the LCX artery (8% of all the hearts). It was larger than the normal sinuatrial nodal artery and supplied the SAN and surrounding area, almost the entire left atrium, and a large part of the interatrial septum and right atrium, as well as part of the AVN area. We found that this artery was present in 5.9% of all cases. Of 34 left sinuatrial nodal arteries, six had an S-shaped configuration. This 18% occurrence corresponds closely to the anatomic dissection data reported by Nerantzis and Avgoustakis. The temporal and spatial resolution of multidetector CT allows definitive localization of this artery where it passes in the groove between the orifice of the left superior pulmonary vein and the mouth of left atrial appendage. A variant of the S-shaped left sinuatrial nodal artery was also seen giving rise to an accessory atrioventricular nodal artery in the transverse sinus at the level of the interatrial septum. This anatomic variant is rare, with only one case report in the literature (16).

The origin of the blood supply to the AVN has been widely studied (17–19). The atrioventricular nodal artery originates from the distal RCA and penetrates the base of the posterior interatrial septum at the level of the crux of the heart in 80%–87% of patients. In the remaining patients, it originates from the terminal portion of the LCX artery (8%–13%) or, uncommonly, from both the RCA and the LCX artery (2%–10%). The classic anatomic concept is that the atrioventricular nodal artery is the main vessel supplying the AVN. According to Anderson and Murphy (18), the vessel supplies the AVN in 90% of hearts but terminates before reaching the node in 10%. Alternative sources of arterial supply to the atrioventricular conducting pathway include the first septal perforating artery; the descending septal artery; and anterior atrial branches, including the Kugel anastomotic artery (18,23–26). CT scanning depicts the relation of the atrioventricular nodal artery to the atrial wall at the base of the Koch triangle. The triangle is demarcated by the Todaro tendon posteriorly and the septal annulus of the tricuspid valve anteriorly. The septal isthmus and the coronary sinus ostium indicate the base of the Koch triangle. The septal isthmus is the area often targeted for ablation of the "slow pathway" in atrioventricular nodal reentrant tachycardia (37). The atrioventricular nodal artery travels very close to the right atrial wall at the base of the Koch triangle (38–41). In our measurements, this distance varied from 1 to 6 mm (mean, 2 mm ± 1). In a study of cadaveric hearts, Sanchez-Quintana et al (39) found that the mean distance of the artery to the endocardial surface at the base of the Koch triangle was 3.5 mm ± 1.5.

The Kugel anastomotic artery was described by Kugel (20) as an atrial artery that arose from the proximal LCX artery and in most cases (66%) anastomosed directly or through its branches with the distal RCA. In the remainder of cases, the same artery formed anastomoses with the proximal RCA (26%) or with branches from the anterior portion of the LCX artery and RCA and the posterior portion of the LCX artery (8%). Nerantzis and colleagues (21) studied 100 human hearts ex vivo by using radiography and direct observation through dissection. In all specimens, they found an anastomotic network of small atrial branches coursing through the lower interatrial septum and connecting indirectly the proximal and distal ends of the larger coronary arteries. In 6% of cases, they showed that the Kugel anastomotic artery, which originated from the proximal LCX artery (3%) or proximal RCA (3%), followed a course independent from the atrioventricular nodal artery and from the small atrial anastomotic network. It was occasionally as large as 1 mm in diameter. Although we observed small atrial branches from sinuatrial nodal arteries in half of our studies, larger atrial vessels with Kugel characteristics were found in only two patients (2.0%). Anastomotic branches with the distal RCA or atrioventricular nodal artery were not seen, probably because of their very small size, which meant they could not be resolved by using current CT spatial resolution. The right Kugel anastomotic artery (21)—also known as the right superior descending (24), right superior septal (25), or descending septal artery (26)—is again part of the atrial anasto-motic network connecting the proximal RCA to the distal RCA or LCX artery. Nerantzis et al (21) found this artery in 3% of the dissected hearts. The right Kugel anastomotic artery was identified in 6% of our patients. In all patients, it was a single vessel and originated from one of three locations, including the proximal RCA trunk, the right sinuatrial nodal artery, and a conus branch.

Our study had limitations. The small size of the study and the predominance of structurally normal hearts in our cohort limit broad generalization of our findings, especially to pathologically altered states. In addition, the anatomy discussed in our study requires a high degree of precision available in vivo only with CT angiography; thus, we had no standard of reference with which we could compare our findings. However, the anatomic agreement of our findings with historical cadaveric dissections of the human heart underlines the validity of our observations. Finally, all classification of the vessels was made by consensus of two reviewers, and we provide no analysis of interobserver agreement on the anatomy of these vessels.

In conclusion, cardiac multidetector CT provides excellent anatomic characterization of the origin, course, and variability of the vessels supplying blood to myocardial conduction tissue, including the SAN and the AVN. Our findings compare well with previously published data obtained from cadaveric dissection and angiographic studies. We believe use of multidetector CT in preprocedural planning for certain catheter-based or surgical procedures potentially involving the human conduction system deserves further investigation.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 


   IMPLICATION FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
References
 


   FOOTNOTES
 

Abbreviations: AVN = atrioventricular node • LCX = left circumflex • RCA = right coronary artery • SAN = sinuatrial node • SVC = superior vena cava

Guarantor of integrity of entire study, F.S.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, F.S., A.R.; clinical studies, F.S., J.N., S.V.G.; statistical analysis, F.S., A.A., O.A., K.K., A.R.; and manuscript editing, F.S., A.A., O.A., J.C.M., J.N.

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE...
 References
 

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