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Anomalous Aortic Origin of the Coronary Artery (AAOCA): Anomalous Right Coronary Artery from the Left Coronary Artery

Overview and Natural History

Anomalous aortic origin of a coronary artery (AAOCA) is a congenital abnormality of the origin or course of a coronary artery that arises from the aorta.1 Normal coronary artery anatomy is characterized by two ostia centrally placed in the right and left sinus of Valsalva. The main left coronary artery (LCA) originates from the left ostium, branching into the left anterior descending artery and circumflex artery, which courses around the left atrioventricular groove; the right coronary artery (RCA) arises from the right ostium, providing an infundibular branch to the anterior side of the heart, and then courses backward in the atrioventricular groove.7 In AAOCA, the origin of one of the coronary arteries is from the wrong sinus of Valsalva.

Epidemiology

AAOCA is the second leading cause accounting for 17% of sudden cardiac death in young athletes in the United States.2 The reported prevalence of AAOCA varies depending on diagnostic method applied: 0.06-0.9% for anomalous right coronary artery (ARCA), 0.025-0.15% for anomalous left coronary artery (ALCA), and 0.02-0.67% for anomalous circumflex coronary artery. 1,3,4

Types

It can be classified based on the origin from the aorta as follows:

  1. Anomalous left coronary artery
  2. Anomalous right coronary artery
  3. Anomalous circumflex coronary artery
  4. Anomalous left anterior descending coronary artery
  5. Single coronary artery

They are further subdivided based on an anomalous course:

  1. Inter-arterial: the coronary artery travels between the aorta and the pulmonary artery
  2. Intra-mural: the coronary artery travels within the aortic wall
  3. Intra-myocardial: the coronary artery travels into the myocardium instead of a normal epicardial course
  4. Retro-aortic: the coronary artery travels behind the aorta
  5. Pre-pulmonic: the coronary artery travels anterior to the pulmonary artery

It is also important to characterize ostial morphology of the anomalous coronary artery which is classified as:1

  1. Round: Antero-posterior diameter equals transverse diameter
  2. Oval: Antero-posterior diameter is 50-90% of transverse diameter
  3. Slit like: Antero-posterior diameter is <50 % of transverse diameter

While echo can diagnose anomalous origin of the coronary artery, technical challenges limit its ability to accurately predict anomalous course and ostial morphology. CT and MRI are useful additional imaging modalities use to define these features if a diagnosis of anomalous coronary artery is suspected.

Hemodynamics

A vast majority of patients with AAOCA are asymptomatic and sudden death can be the first manifestation in some patients. There is no clear consensus on the mechanisms of ischemia in AAOCA. Presumably, compression of anomalous coronary artery occurs during exercise, leading to myocardial ischemia and ventricular fibrillation/tachycardia. Proposed mechanisms for coronary compressions include: 1,5

  1. Compression of intra-mural segment by aortic expansion during exercise
  2. Torsion, compression or kinking of inter-arterial coronary artery during exercise
  3. Slit like ostia and flap like closure of the coronary artery during exercise
  4. Vasospasm of coronary secondary to endothelial damage
  5. Hypoplastic coronary artery that predisposes to insufficient blood flow and ischemia

Goals of echocardiography

Echocardiogram is an excellent tool to screen for coronary anomalies in children. Important views in transthoracic echocardiogram include: 6

  1. Parasternal short axis 2D and color Doppler: This view helps to define the origin (single versus two ostia) and the proximal course of a coronary artery (inter-arterial versus intra-mural segment). In order to demonstrate inter-arterial/intra-mural course of anomalous left coronary artery, subtle clockwise rotation of the transducer from the standard parasternal short-axis view can be performed. Likewise, inter-arterial/intra-mural course of anomalous right coronary artery can be obtained by moving the transducer medially and subtle anti-clockwise rotation.
  2. Parasternal long axis 2D and color Doppler: This view demonstrates the origin of the coronary artery in relation to the sinotubular junction (normal origin versus high origin) and also the proximal course of the coronary artery.
  3. Modified high parasternal short and long axis views:  Helpful to define the proximal course of the coronary artery.

It is recommended to use high-frequency probes and small sector width to optimize high spatial and temporal resolution. Generally, 3-5 beats clip is preferred and still frames should be avoided.

 

References
1.     Mery CM, Lawrence SM, Krishnamurthy R, Sexson-Tejtel SK, Carberry KE, McKenzie ED, Fraser CD. Anomalous Aortic Origin of a Coronary Artery: Toward a Standardized Approach. Seminars in Thoracic and Cardiovascular Surgery. 2014;26:110–122.
2.     Maron BJ, Doerer JJ, Haas TS, Tierney DM, Mueller FO. Sudden deaths in young competitive athletes: analysis of 1866 deaths in the United States, 1980-2006. Circulation. 2009;119:1085–1092.
3.     Prakken NH, Cramer MJ, Olimulder MA, Agostoni P, Mali WP, Velthuis BK. Screening for proximal coronary artery anomalies with 3-dimensional MR coronary angiography. Int J Cardiovasc Imaging. 2010;26:701–710.
4.     Pelliccia A, Spataro A, Maron BJ. Prospective echocardiographic screening for coronary artery anomalies in 1,360 elite competitive athletes. The American Journal of Cardiology. 1993;72:978–979.
5.     Angelini P. Novel Imaging of Coronary Artery Anomalies to Assess Their Prevalence, the Causes of Clinical Symptoms, and the Risk of Sudden Cardiac Death. Circulation: Cardiovascular Imaging. 2014;7:747–754.
6.     Lorber R, Srivastava S, Wilder TJ, McIntyre S, DeCampli WM, Williams WG, Frommelt PC, Parness IA, Blackstone EH, Jacobs ML, Mertens L, Brothers JA, Herlong JR, AAOCA Working Group of the Congenital Heart Surgeons Society. Anomalous Aortic Origin of Coronary Arteries in the Young: Echocardiographic Evaluation With Surgical Correlation. JACC Cardiovasc Imaging. 2015;8:1239–1249.
7.     Hauser M. Congenital anomalies of the coronary arteries. Heart. 2005; 91(9): 1240-1245
 
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