The Right Subclavian Artery Arising as the First Branch of a Left-Sided Aortic Arch.

We describe an unusual pattern of branching of a left-sided aortic arch in which the first branch is the right subclavian artery, followed by the common carotid arteries arising from a common trunk. The patient was born with transposition (concordant atrioventricular and discordant ventriculoarterial connections) and had 18q23 deletion. We discuss the implication of these anatomic findings in the light of inferences currently made by echocardiographers when the first branch of the aortic arch fails to bifurcate. We also relate the findings to the concepts of cardiac development and draw comparisons with previous descriptions, and interpretations of the morphogenesis, of the patterns of branching from the aortic arch.