Anomalous left coronary artery from the pulmonary artery (ALCAPA)


Anomalous left coronary artery from the pulmonary artery (ALCAPA), also known as Bland-White-Garland syndrome, is a rare coronary artery anomaly that affects 1 in 300,000 live births 1.  ALCAPA arises from either abnormal septation of the aorta and the pulmonary artery or from the persistence of aortic buds that form the coronary arteries 2.  It can occur as an isolated anomaly or in conjunction with other lesions such as atrial septal defect, ventricular septal defect and coarctation of the aorta 3.

In fetal life, the pulmonary artery pressure equals systemic pressure, allowing for satisfactory myocardial perfusion from the pulmonary artery through the anomalous coronary artery.  After birth, the pulmonary artery contains desaturated blood at a pressure that rapidly falls below systemic pressure.  As pulmonary arterial pressure drops, the combination of low flow and desaturated blood causes myocardial ischemia, especially during exertion.  Collateral vessels develop between the right and left coronary arteries and may provide adequate perfusion to the left myocardium.  Further decrease in pulmonary arterial pressure results in a reversal of flow, as the left coronary artery drains from the right coronary artery, through the collaterals, into the pulmonary artery (left-to-right shunting).  This is known as myocardial steal phenomenon, which may cause ischemia or infarction of the anterolateral left ventricular wall.  Patients who survive to adulthood may develop a good collateral network with tortuous and dilated left and right coronary arteries 1-5.