The essence of so-called heterotaxy is the potential disharmony between the arrangement of the bronchuses, abdominal organs, and the atrial appendages. Accurate description of the heart, however, can only be provided by specific description of these features, all of which are readily discernible in the clinical setting. We argue that, when accurate description of the atrial and visceral arrangement is provided, along with appropriate description of the intracardiac findings, no further accuracy is gained by suggesting that an individual heart is “heterotaxic”.

Use of correct nomenclature is important in all aspects of medicine. Many of the controversies that have bedeviled paediatric cardiology have devolved from the inappropriate use of words to describe the lesions to be found when the heart is congenitally abnormal. A continuing area of disagreement is the situation currently described by many as representing “heterotaxy”. When used literally, this word means any departure from the normal. Thus, all congenitally malformed hearts represent examples of heterotaxy. By convention, nonetheless, the term is used to describe the arrangement in which the bodily organs, including parts of the heart, are not in their usual or in their mirror-imaged patterns. The arrangements, therefore, represent the presence of the organs on the right and left sides of the body being mirror imaged, in other words isomeric; however, not all the organs are uniformly isomeric. In this review, we show that, when assessed on the basis of the morphology of the atrial appendages, specifically the extent of the pectinate muscles relative to the atrioventricular junctions, isomerism is an unequivocal finding within the heart. Only the atrial appendages, however, are truly isomeric. The potential problem of disharmony between the various systems of organs is resolved simply by accounting specifically for each of the systems. On these bases, we suggest that the isomeric arrangements can now readily be diagnosed in the clinical setting, and differentiated into their right and left isomeric variants. We propose that such distinctions will provide the key for establishing the genetic cues responsible for the formation of the isomeric as opposed to the lateralised arrangements.

Isomerism of the left atrial appendages is often associated with cyanosis due to intracardiac structural abnormalities such as common atrium and/or anomalous pulmonary or systemic venous connections. We report two cases of children with cyanosis and left isomerism but no other lesions within the heart. In these cases, multiple small pulmonary arteriovenous malformations were found bilaterally, resulting in intrapulmonary right-to-left shunting and systemic desaturation.

Either arrangement of the abdominal vessels or the morphology of the bronchial tree are usually used to predict atrial arrangement. We report a patient in whom, in the setting of normal physiology as seen with mirror-imaged venous return, and due to disparity between the arrangement of the abdominal vessels (suggestive of right isomerism) and thoracic arrangement (indicative for left isomerism), atrial arrangement could not be inferred. Direct echocardiographic imaging of both appendages revealed left isomerism.

To date, almost all patients reported with hypoplasia of the left heart have had usual atrial arrangement, with a small proportion known to have left or right isomerism. As far as I am aware, however, only one patient has previously been described with mirror-imaged arrangement of the heart and organs. In this report, I describe the second case.