title: What is aortic overriding?
abstract: BACKGROUND
  Disagreement currently exists regarding the definition of aortic dextroposition. It is suggested that the term be used interchangeably with aortic overriding, along with suggestions that the aortic valve overrides in the normal heart. The dextroposed aorta, however, does not always override the crest of the muscular ventricular septum. It is incorrect to argue that the normal aortic valve overrides. It is the cavity of the right aortic valvar sinus, rather than the valvar orifice, that sits above the muscular septum when the septum itself is intact. Therefore, to circumvent these difficulties, those using the term "dextroposition" find it necessary to distinguish "true" as opposed to "false" categories. The problems arise because "dextroposition" is remarkably ill-suited as an alternative term for aortic valvar overriding.
  
  
  RESULTS
  In this review, combining developmental, morphologic, and clinical data, we show how aortic overriding is best considered on the basis of biventricular connection of the aortic root in the setting of deficient ventricular septation. When analysed in this manner, it becomes an easy matter to distinguish between one-to-one and double outlet ventriculo-arterial connections. Appreciation of these features emphasises the different spatial alignments of interventricular communications as opposed to the plane of deficient ventricular septation. The concept of overriding is applicable not only to biventricular connection of the aortic root, but also the pulmonary and common arterial roots.
  
  
  CONCLUSIONS
  The diagnostic techniques now available to the paediatric cardiologist illustrate the features of arterial valvar overriding with exquisite accuracy, informing the discussions now required for optimal decision making.
authors.affiliation: 1Institute of Genetic Medicine,Newcastle University,Newcastle,United Kingdom.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Anderson
authors.affiliation: 2Department of Pediatric Cardiology,University of Florida,Gainesville,Florida,United States of America.
authors.forename: Diane E
authors.initials: DE
authors.lastname: Spicer
authors.affiliation: 4Emeritus Founding Editor,Chapel Hill,North Carolina,United States of America.
authors.forename: G William
authors.initials: GW
authors.lastname: Henry
authors.affiliation: 5Department of Medical Imaging,Ann and Robert H. Lurie Children's Hospital,Chicago,Illinois,United States of America.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Rigsby
authors.affiliation: 6Division of Pediatric Cardiology,Medical University of South Carolina,Charleston,South Carolina,United States of America.
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Hlavacek
authors.affiliation: 7Division of Developmental Biology,MRC National Institute for Medical Research,London,United Kingdom.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Mohun
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000002:abnormalities* / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006330:Heart Defects, Congenital / Q000145:classification / Q000175:diagnosis / Q000503:physiopathology; D006349:Heart Valve Diseases / Q000151:congenital*; D006801:Humans; D051379:Mice; D011859:Radiography; D009626:Terminology as Topic; D013771:Tetralogy of Fallot / Q000175:diagnosis
keywords: cardiac development