Juxtaposition of the morphologically left atrial appendage in solitus and inversus atria: a study of 18 postmortem cases.

Juxtaposition of the morphologically left atrial appendage (JLAA) was analyzed for the first time primarily morphologically, rather than primarily positionally. In a series of 18 postmortem cases, JLAA with solitus atria occurred in 16 (89%) cases, and JLAA with inversus atria was found in 2 (11%) cases. JLAA with solitus atria was always right-sided, whereas JLAA with inversus atria was left-sided. Thus the sidedness of the malposed (juxtaposed) LAA depended on the atrial situs, not on the type of ventricular loop (contrary to what was formerly thought). The anatomic features associated with JLAA are essentially the opposite of those with JRAA. JLAA was characterized by left atrial outlet obstruction (69%), left ventricular hypoplasia (67%), and aortic outflow tract obstruction (39%). JLAA usually has a hypoplastic left ventricle and normal conus, whereas JRAA typically has a hypoplastic right ventricle and abnormal conus.