Isomerism or heterotaxy: which term leads to better understanding?

Abstract

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.

Has the Congenitally Malformed Heart Changed Its Face?

“…7 Recent findings show that their phenotypic features are those of isomerism, as opposed to lateralization, of the thoracic organs. 13 For the heart, however, it is only the atrial appendages that are truly isomeric. By perturbing the genetic cascades responsible for producing morphologically rightness or leftness, it is now possible to generate mice with either isomeric right (Figure [C]) or left ( Figure [D]) atrial appendages.…”

Cardiac Embryology and Molecular Mechanisms of Congenital Heart Disease: A Primer for Anesthesiologists

“…18,52 A more contemporary approach advocates segregation of heterotaxy patients by morphology of the atrial appendages, as isomerism in the heart is predominantly restricted to the atria. 53,54 Determination of atrial isomerism primes the evaluator to seek specific intracardiac abnormalities, such as univentricular atrioventricular connections, absence of the coronary sinus, pulmonary atresia/ stenosis and totally anomalous pulmonary connection which are frequently associated with isomeric right atrial appendages, while interruption of the inferior caval vein and aortic coarctation are more frequently encountered in individuals with isomeric left atrial appendages. 53 Determination of atrial isomerism can be determined clinically with computed tomography angiography 55 or echocardiography.…”

Genetic Disturbances in Patients with Bodily Isomerism from a Single Center: Clinical Implications of Affected Genes and Potential Impact of Ciliary Dyskinesia

“…1,2 As a result, both bronchuses are either long and hyparterial, making them morphologically left, or short and eparterial, meaning that they are morphologically right. The lungs usually share the same morphological sidedness as the bronchuses, with either bilobed or trilobed lungs being present bilaterally.…”