FIG 46.1 Dissection, viewed from the left side, showing anomalous origin of an accessory coronary artery feeding the left ventricle but arising from the left subclavian artery The major left coronary artery itself arises anomalously from the right coronary aortic sinus and extends between the arterial trunks FIG 46.2 Origin of the main stem of the left coronary artery from the pulmonary trunk Early diagnosis permits rapid surgical correction In most instances, the artery arises from the sinus of the pulmonary trunk adjacent to the left coronary aortic sinus (Fig 46.3).4 Less frequently, the artery can arise from a branch of the pulmonary trunk, including the right pulmonary artery It takes a much longer course to reach the heart (Fig 46.4) Clinical evolution depends on the extent of development of a collateral circulation The artery arising from the pulmonary circuit is usually small and thin walled The RCA, which retains aortic origin, undergoes compensatory enlargement If the collateral circulation is well developed and distributed, the left ventricle can remain well perfused, with the heart retaining its form and function More frequently, the collateral circulation is poorly developed The left ventricle becomes ischemic, dilated, infarcted, and fibrosed (Fig 46.5) This appearance can mimic dilated cardiomyopathy, particularly if the fibrosis involves the papillary muscles, producing mitral valvar incompetence Hence anomalous pulmonary origin of a coronary artery must always be excluded when considering the diagnosis of dilated cardiomyopathy in childhood If the RCA is taking ectopic origin, it usually arises from the pulmonary valvar sinus adjacent to the right coronary aortic sinus Origin of both coronary arteries from the pulmonary trunk is very rare but can be diagnosed in life and treated surgically.5 FIG 46.3 Sites of origin of the anomalous left coronary arteries from the pulmonary trunk reported by Smith and colleagues5 have been superimposed on the normal pulmonary root, shown with the root opened anteriorly and the leaflets of the pulmonary valve removed The right-facing sinus is described as seen from the aspect of the observer standing, figuratively speaking, in the nonadjacent sinus of the pulmonary trunk, and looking toward the aortic root The numbers indicate the cases arising from the position shown in the right-facing sinus, which is adjacent to the putative left coronary aortic sinus FIG 46.4 Origin of the left coronary artery from right pulmonary artery