Invited Commentary: Left Isomerism or “Isolated Atrial Inversion”?

Abstract

In the accompanying article, Chenu and colleagues describe “an uncommon course of the right superior vena cava in a patient with heterotaxy syndrome.” In their discussion, they pose the question, “Is this an isolated atrial inversion, or a case of left isomerism?” They proceed to comment “this remains a debate among cardiac morphologists.” I can agree with them on their first description, since although I have previously examined many hearts from patients with isomerism of the left atrial appendages, or “polysplenia syndrome,” I had not noticed the unusual feature they have emphasized in their case report; although, as I will show, the evidence was there for me to observe their feature of emphasis. They deserve great credit, therefore, for bringing this feature to our attention. I also agree with their first statement, namely that their patient has the left isomeric variant of the so-called visceral heterotaxy, but I must question their suggestion that the patient may exhibit mirror-imaged arrangement of the atrial chambers or “atrial situs inversus.” I would question even more strongly their comment that the distinction remains “a debate among cardiac morphologists.” As I will further show, the distinction has major clinical implications, not only for pediatric cardiac surgeons but also for those involved with genetic counseling.