DESCRIPTION

The anomalous left coronary artery arises from the pulmonary artery rather than from its usual origin, the aorta. This is commonly referred to as ALCAPA or Bland-White-Garland syndrome.

EPIDEMIOLOGY

• Rare anomaly affecting 1 in 300,000 live births and occurring in 0.2–0.5% of cases of congenital heart disease
• The majority of patients present in infancy at approximately 2 months of age when pulmonary vascular resistance (PVR) falls.
• There are case reports of patients presenting as late as the 4th to 8th decades of life.

ETIOLOGY

Two theories:

• Abnormal septation of the conotruncus into the aorta and pulmonary artery
• Persistence of the pulmonary buds and involution of the aortic buds that usually form the coronary arteries

PATHOPHYSIOLOGY

• In the fetal and neonatal period, PVR is increased relative to systemic vascular resistance providing the driving force for antegrade flow from the pulmonary artery through the anomalous coronary artery to supply the ventricular myocardium.
• As PVR drops, pulmonary arterial pressure drops. When the diastolic blood pressure in the pulmonary artery decreases below myocardial perfusion pressure (i.e., diastolic aortic pressure), pulmonary run-off “steals” blood from the myocardium, resulting in myocardial ischemia.
• In ALCAPA, ischemia of the anterolateral left ventricular wall occurs leading to left ventricular and mitral valve papillary muscle dysfunction.
• The fact that the ventricle is perfused with desaturated blood plays a less important role than the overall perfusion-related imbalance between myocardial oxygen demand and supply.