Origin of Right Coronary Artery (RCA): A Multidetector Computed Tomography (MDCT) Coronary Angiographic (CA) Study in North India

Introduction: Several clinical and pathological scenarios like hemodynamic procedures, cardiac surgery in heart trauma and arrhythmias from coronary occlusive disease management have importance of variations in the origin of Right Coronary Artery (RCA). The RCA presents a wide spectrum of morphological expressions regarding its sites of origin, course, branches, length, size and termination. RCA usually arises from the Anterior Aortic Sinus (AAS) and traverses through the right atrio-ventricular (AV) groove. Subjects and Methods : In the present study, Computed Tomographic (CT) coronary angiograms of 50 routine subjects of different age groups who came to the Department of Radiodiagnosis, King George’s Medical University UP, Lucknow in the year 2010- 2011 with known or suspected coronary artery disease, were analyzed. Coronary angiography (CA) was performed on a 64 slice Multidetector Computed Tomographic (MDCT) scanner, using retrospective electrocardiographic (ECG) gating. The incidence of different sites of origin of RCA was assessed. Results: In the present study, RCA originated from Anterior Aortic Sinus (AAS) in 47 (94%) subjects. In 3 (6%) subjects, RCA showed anomalous origin from Left Posterior Aortic Sinus (LPAS). These three subjects were males [3(9.38%)]. In all the subjects, the course of RCA was normal except three males having origin of RCA from LPAS. In these three males, the proximal part of RCA coursed between Right Ventricular Outflow Tract (RVOT) and aorta. Conclusion: Most common site for origin of RCA was AAS. Anomalous origin of RCA was seen only from LPAS. Anomalous origin of RCA was seen only in male subjects. In all subjects having anomalous origin of RCA from LPAS, RCA coursed between pulmonary trunk and ascending aorta. circumflex


Introduction
The Right Coronary Artery (RCA) presents a wide spectrum of morphological expressions regarding its sites of origin, course, branches, length, size and termination. The knowledge of these variations is extremely important for their implications in surgical procedures and clinical events. RCA arises from the anterior ('right coronary') Aortic Sinus (AAS). The artery reaches the crux of the heart and ends a little to the left of it, often by anastomosing with the circumflex branch of left coronary artery. [1] Anomalous origin of RCA is a rare congenital anomaly that was first described in 1948 by White NK and Edwards JE. [2] In an angiographic study, Yamanaka O and Hobbs RE described that anomalous origin of RCA from left sinus of Valsalva, is a congenital abnormality with 0.107% incidence. [3] Topaz O, et al found that the RCA is the most common anomalous vessel. [4] Congenital coronary anomalies are associated with sudden death and exercise-related death. Taylor A J, et al observed that anomalous origin of RCA from left coronary sinus was the second most frequent anomaly and they reported that there is risk of sudden cardiac death with exercise in younger patients (less than or equal to 30 years old) with an isolated coronary artery anomaly. With age, the risk of sudden death decreases. Younger patients (less than or equal to 30 years old) were significantly more likely than older patients (greater than or equal to 30 years old) to die suddenly or during exercise despite their low frequency of significant atherosclerotic coronary artery disease. [5] Anomalous aortic origin of a coronary artery (AAOCA) is the second most common cause of sudden cardiac death (SCD) in young athletes. It is postulated that occlusion or compression of the anomalous coronary artery during exercise leads to myocardial ischemia and subsequent lethal ISSN (0): 2455-5274; ISSN (P):  Tomar et al; Origin of Right Coronary Artery ventricular arrhythmia (ventricular tachycardia and fibrillation). According to available evidences the prevalence of anomalous right coronary artery (ARCA) is approximately six times more than anomalous left coronary artery (ALCA). [6] RCA may arise from different anomalous sites. Cansel M, et al reported origin of RCA from Left Anterior Descending (LAD) artery which is a very rare coronary anomaly. [7] Zamani J and Mahmmody Y reported origin of RCA from LCA. [8] RCA arising from the main LCA accounts for only 0.65% of coronary artery anomalies. [9] Kragel AH and Roberts WC studied the correlation between coronary dominance and anomalous origin of coronary artery and they found that the coronary dominance is useful to distinguish clinically significant anomalies from clinically insignificant anomalies. [10] The incidence of coronary anomalies in patients undergoing coronary angiography varies from 0.64% to 1.3%. Many of these anomalies are clinically benign; however, others are associated with serious morbidity. [11] Knowledge of normal anatomy of RCA and its variations or anomalies is of paramount importance in heart surgeries. Inability to detect these anomalies may lead to complications. [12] Several clinical and pathological scenarios like hemodynamic procedures, cardiac surgery in heart trauma and arrhythmias from coronary occlusive disease management have importance of variations in the origin of RCA. The aim of this study was to assess the incidence of different sites of origin of RCA in subjects of North India and to find any anatomic variant.

Materials
In this study, digital copies of CT coronary angiograms of 50 subjects of both sex and different age groups [32 males (14-75 years), 18 females (12-70 years); mean age 51.36±14.07 years, age range 12-75 years] were analyzed after taking due permission from Institutional Ethical Committee.

Method
This was an observational study. Coronary Angiography (CA) was done on patients came to the Department of Radiodiagnosis, King George's Medical University UP, Lucknow in the year 2010-2011 with known or suspected coronary artery disease.

Inclusion criteria
Patients presenting with symptoms and signs of cardiovascular diseases e.g. Chest pain and Dyspnoea.
(3) Allergy to contrast agent. (4) Contraindication to radiation exposure (e.g. pregnancy).  Pre-procedure precautions • The subjects were enquired, to rule out the presence of any drug allergy to avoid the occurrence of any untoward anaphylactic reaction during the procedure. • Two days prior to the procedure the subjects were advised to avoid the intake of fatty food. • They were advised to drink only water just prior to the procedure. • Blood urea and creatinine levels were evaluated.

Procedure
The subjects were laid supine. Their heart rate was stabilized with an oral dose of 50-100 mg Metoprolol one hour before the scan. If heart rate was not stabilized with an oral dose, then intravenous (IV) Metoprolol was given. Electrocardiogram (ECG) and pulse rate were monitored half an hour prior to the procedure. The subjects were counseled to reduce their anxiety. The subjects were connected to a cardiac monitor. For venous access, an upper extremity vein (antecubital vein) and a 20-gauge intravenous canula was used. 80-85 ml of non-ionic contrast Iohexol (Omnipaque, GE, GE Healthcare Ireland, Cork) containing iodine concentration of 350 mgI/ml, injected with a flow rate of 5.5ml/sec, followed by a 20 ml saline flush at a rate of 4ml/sec with a pressure injector (PSI-325). The scan timing was determined with automated bolus tracking technique by placing the region of interest over mid ascending aorta and setting the trigger threshold to 180 Hounsfield (Hu). The subjects were asked to lie still on the "scanning bed" for a period of 5-10 minutes. The instruction was given to the subjects to maintain an inspiratory breath hold during which CT data and ECG tracings were taken. CTCA was performed 5 seconds after aortic peak density. Scanning coverage was from the level of carina to the bottom of the heart. Raw spiral CT data of coronary arteries were reconstructed in various phases of cardiac cycle on a work station (Brilliance 64 version 4.5) to obtain images with the highest quality (without motion artefact).Reconstruction performed at 75% of R-R interval was found to be optimal for image analysis in most of the subjects. In some, if heart rate could not be stabilized properly, then reconstructions were performed at 45% of R-R interval. The images generated were reconstructed and viewed utilizing a separate workstation which enabled generation of the coronary arteries in the standard and in various other anatomical planes as and when required and were interpreted with the help of a cardiac radiologist. Subjects with previous bypass surgery and also those with suboptimal study due to breath hold artefacts were excluded. All images were reviewed first in axial projection and then with post processing tools such as Multiplanar Reconstruction (MPR), Curved Planar Reformation (CPR), thin-slab Maximum Intensity Projection (MIP), and Volume-Rendering Technique (VRT) with transparent background display. MIPs were obtained using various thicknesses (5-30 mm). Volume-rendered (VR) images were also obtained using various orientations. CTCA images were observed for the origin of RCA. The

Discussion
The origin of coronary arteries shows great variability. [1] Several studies have been done in the past regarding the origin of RCA [  Table 3]. [13] In some cadaveric studies, RCA arose from AAS in 100% cases[ Table 3]. [14][15][16][17][18]    . After analyzing the findings of these studies, we found that the most common site for anomalous origin of RCA is LPAS. Chaitman BR, et al observed that aberrant ostium of RCA in LPAS is invariably in front of the ostium of LCA. [19] But orifice for the ectopic RCA may be present posterior to the left main ostium as found by Yamanaka O and Hobbs RE. [3] There are three subtypes of this anomalous RCA based on the anatomic course. Retroaortic, if the anomalous artery traverses posterior to the ascending aorta; Interarterial, if it runs between the ascending aorta and pulmonary trunk and in third variant it courses anterior to the pulmonary trunk. [20] In some studies, it is reported that the RCA coursed anterior to aorta in patients in whom it originated from LPAS. [19,[21][22][23][24][25][26][27][28] In the present study also, anomalously originated right coronary arteries coursed anterior to aorta. RCA is at high risk when it arises from LPAS and coursed between pulmonary artery and aorta. [5] Shu-shui W, et al named this kind of aberrant RCA with interarterial course as 'Coronary Artery Sandwich Anomaly. [29] Ziegler FV, et al reported proximal intramural course of anomalous RCA originated from left sinus of Valsalva. [30]  In the present study, anomalous origin of RCA was seen only from LPAS, and it was observed in 3 (6%) cases [ Table  2 & 6]. This incidence was quite high. Anomalously originated RCA is a rare congenital cardiac malformation. [24] Houman TM, et al reported that anomalously originated RCA from left sinus of Valsalva is a rare congenital anomaly but frequently causes sudden death in the young. They also suggested that early graft failure had occurred if bypass procedures are used to treat such kind of anomalous origin of RCA. [31] This kind of ectopic RCA is difficult to cannulate because of its slit-like orifice and odd angulation. [3] Several authors found that RCA is the most common anomalous vessel among coronary arteries. [4,23,27,[32][33][34] While some authors found RCA as the second most common anomalous coronary artery. [35][36][37] Anomalous origin of RCA is often asymptomatic and is found incidentally during evaluation of some cardiac diseases. [38] Although origin of RCA from the left sinus of Valsalva and course between the aorta and pulmonary artery is less frequently associated with symptoms, this condition may be associated with sudden death. [39] In a CT angiographic study, Krupinski M, et al observed that high-risk anatomy features are most common in patients with abnormal RCA origin. These patients also have higher prevalence of chest pain and tend to show higher occurrence of cardiac events in the follow-up than individuals with abnormal LCA origin and abnormal LCx artery origin. [40] Anomalous origin of coronary arteries from aorta is uncommon but significant clinically. Clinical manifestations may vary from asymptomatic patients to those who present with heart failure, syncope and arrhythmias. [41] Anomalous origin of the coronary arteries may be a risk factor for angina pectoris, acute myocardial infarction and sudden death even if there is no atherosclerosis. [23] Roberts WC, et al found fibrosed myocardial patches, small areas of infarcts in patients who suffer sudden death in absence of atherosclerosis. [42] Frescura C, et al observed that in 16 patients out of 27 with isolated anomalous origin of coronary arteries, the final outcome was sudden death. Sudden death occurred in 43% of right coronary artery origin from left aortic sinus. [43] Clarification of the risk and mechanisms of sudden death in patients with coronary anomalies may aid in decisions on intervention. Taylor A J, et al proposed the mechanism of myocardial ischemia and sudden death in these patients and proposed causes include:1) Ostial obstruction due to slit-like coronary orifice.
2) Compression of RCA between aorta and pulmonary artery. 3) Stretching of the RCA with aortic/pulmonary artery distension. Coronary angulation with aortic / pulmonary artery distension. [5] Singhi AK, et al stated that anomalously arising RCA from left coronary sinus can have dynamic narrowing and kinking causing myocardial ischemia and sudden cardiac death. Anomalous artery should be surgically repaired in the symptomatic patients because of risk of ischemia or ventricular arrhythmia and a close follow up is required in asymptomatic patients with exercise restriction as per present guideline. [44] Targeted patients for treatment are those whose anomalous artery is dominant, whose anomalous artery is having proximal intramural course and those who become symptomatic before 35 years of age. [41] Cheatham JP, et al reported origin of RCA from descending thoracic aorta and found atypical and elastotic changes and wall thickening in this RCA. [45] According to Yamanaka O and Hobbs RE, origin of the RCA from pulmonary artery is extremely rare. They found origin of RCA from pulmonary trunk in 2 cases, which is a potentially serious anomaly. [3] Rigatelli G, et al and HakimK, et al reported anomalous origin of RCA from pulmonary artery. [46,47] In a cadaveric study, Vasuki AKM, et al found origin of RCA from pulmonary trunk in three specimens out of fifty. [48] Some authors have reported origin of RCA from LCA. [4,8,9] While some have observed origin of RCA from LAD artery. [7,[49][50][51][52][53] Duran C, et al also reported absence of RCA in one case. [ [36,56] If RCA takes origin from above the Sino-tubular (ST) junction, then it is known as high take-off of RCA. In the present study, no case of high take-off of RCA was found whereas several authors reported high take off of RCA. [3,14,24,27,28,43,[57][58][59][60][61] Sahni D and Jit I reported an incidence of 3.4% in males and 1.7% in females. [57] High takeoff of the coronary arteries usually presents no major clinical problems, but may cause difficulty in cannulating the vessels during coronary arteriography. Selective intubation of the coronary artery may be extremely difficult, especially when the RCA is anomalously located high over the left coronary sinus. [62] Angelini P, et al reported low origination of RCA. [63] Anomalous coronary arteries may be found as an isolated defect or may occur as a part of congenital malformations of the heart. A high incidence of congenital heart diseases was reported by Topaz O, et al in cases of anomalous coronary arteries. Recognition of these anomalous arteries is important in patients undergoing coronary angioplasty or cardiac surgery. [43] In some catheter angiographic studies, the incidence of primary congenital anomalies of coronary arteries is more in males than females. [21,32,35,64] But in a study done by Aydar Y, et al, the incidence found more for females. [55] Cardiac surgeons should take care of anomalous coronary arteries in order to avoid transsection, ligation, or iatrogenic occlusion of anomalous arteries during surgery. [65] Anomalously originated coronary arteries are the second most common cause of athletic-field deaths in the United States. [66] Why an athlete can exercise intensely for several years without symptoms until the sentinel event occurs remains unknown. [6] Jim MH, et al stated that the RCA anomalously arising from left coronary sinus is associated with early development of Coronary Artery Disease (CAD) while Suryanarayana P, et al found that there is no difference in the occurrence of atherosclerosis between anomalous and nonanomalous coronary arteries. [34,67] Coronary artery anomalies should be recognized during life time of a patient by the use of noninvasive procedures to prevent the risk of sudden death and to plan surgical correction if clinically indicated. [43]

Conclusion
In the present study, most common site for origin of RCA was AAS. Anomalous origin of RCA was seen only from LPAS. Anomalous origin of RCA was seen only in male subjects. In all subjects having anomalous origin of RCA from LPAS, RCA coursed between pulmonary trunk and ascending aorta.