What is COSA?

CORONARY OSTIAL STENOSIS AND ATRESIA (COSA)

• COSA is a rare congenital coronary anomaly which affects the left coronary artery more frequently than the right coronary artery.  

• The aortic ostium in a case of COSA can be in the normal location or at an ectopic site.

• Atresia of the left main coronary artery is characterised by the congenital absence of the left main coronary ostium and left main trunk with normally connected left anterior descending and circumflex arteries which proximally end blindly. 

• These patients are able to survive via congenitally developed collateral circulation from either the conus branch artery (Vieussens’ anastomotic ring) or through the right coronary artery (retroaortic Kugel’s ring),  anterior ventricular branches of the right coronary artery or  through the terminal ramifications of the posterior descending branch with retrograde flow to the terminal branch of the left anterior descending artery at the apex of the left ventricle.  

• The presence of only 1 or 2 full-diameter connecting collateral vessels (without narrowing at the transition between the providing and the receiving vessel) is suggestive of congenital origin. Whereas in cases of postnatally acquired collateral vessels as in atherosclerotic coronary artery disease or anomalous origin of coronary artery from pulmonary artery, there is a rich network of collateral vessels. 

• Almost all patients eventually develop myocardial ischemia as the collateral circulation from the right to the left coronary is not adequate to the heart’s metabolic needs. Also, due to the long course of the collateral, blood reaches the left coronary artery during systole and this abnormal timing also contributes to the development of myocardial ischemia. 

• This entity differs from single coronary artery as in the latter the blood flow is always centrifugal, flowing from the center to the periphery, and from bigger to smaller arteries. There are no collaterals or interruption of continuity in single coronary artery. Whereas in left main coronary atresia blood flows from the right to the left coronary artery via one or more collateral arteries whose calibre is smaller. 

• Physiologically, coronary ostia atresia is usually associated with ischemic manifestations, whereas single coronary artery is not. 

• This congenital atresia should also be differentiated from acquired causes ostial or proximal coronary stenosis, such as arteritis (atherosclerotic, syphilitic, Kawasaki, and Takayasu aortitis). Differentiating factors include an absence of significant risk factors for atherosclerosis, presence of ostial dimple which is a rudiment of coronary ostium and blind distal left main trunk in congenital coronary atresia.