How do we determine atrial arrangement?

and his colleagues present a detailed and careful analysis of the arrangement of the heart and thoraco-abdominal organs in a large series of over one thousand autopsied patients.1 Their findings bear directly upon the controversy in which I was recently involved at the 3rd World Congress of Pediatric Cardiology and Cardiac Surgery. The controversy sessions took place on the last day of the Symposium. My debate, carried out with Dr Steve Sanders from Duke University, was concerned with the proposition “There is no such thing as Isomerism in the Heart”. It attracted a relatively limited audience. This was a pity, since the scienti fic arguments presented from both sides, as viewed from my obviously biased stance, were formidable. Many of the points we discussed are highlighted in the excellent results and discussion presented here by the team from Caracas. As has been argued strongly in recent years, it is my own belief that the evidence supporting the existence of cardiac isomerism is overwhelming.2–4 Within the human heart, however, specifical ly when it is congenitally malformed, my diagnosis of the presence of isomerism is based exclusively on the arrangement of the atrial appendages. This point needs to be born in mind by those who read the extensive study of the Venezuelan team.1 MachadoAtias and his colleagues make many points with which I agree most strongly. They make one suggestion which is particularly important. This bears on one of the criticisms made by Steve Sanders of my own approach to isomerism. In his presentation in Toronto, Steve pointed out that the term “isomerism” was basically derived from the physical sciences. He argued that chemical isomers were exact mirror-images of each other. In the field of biological science, it is very unusual to find exact mirror-imagery. Even in the situation of the limbs, which are essentially mirror-imaged relative to each other, features such as hypertrophy or atrophy of one limb can obscure the basic situation. Considering the heart and thoraco-abdominal organs with this in mind, specifical ly in the situation of visceral heterotaxy, Machado-Atias and colleagues suggest that the more appropriate term would be “isomorphism”. This is the noun they use throughout their description, and all the logical arguments support its use. W hether this means that it will meet with widespread approbation, and enter the terminological lexicon, will only be established on the basis of future usage. W hilst supporting Machado-Atias and his colleagues in the use of isomorphism, however, there is one area in which we continue to disagree. The team from Caracas have shown great patience with me during the process of review, but we have stil l to reach final agreement on this one outstanding point. Machado-Atias and his colleagues argue that, in three of their cases with heterotaxy, there is discordance between arrangement of the atriums and the atrial appendages. I find this an impossible statement since, for me, the diagnosis of atrial arrangement is based entirely upon the recognition of the morphology of the appendage. This does not depend upon the shape of the appendage, nor on the presence or absence of the terminal crest, nor on their size. All of these features can be distorted by extraneous agencies. Our definition of the anatomic nature of the appendages is based exclusively on the extent of the pectinate muscles lining the wall of each appendage relative to the atrioventricular junction. In the normal heart, these pectinate muscles in the morphologically right appendage extend all round the vestibule of the tricuspid valve and reach to the crux of the heart. The morphologically left appendage has its pectinate muscles confined within Cardiol Young 2001; 11: 482–483 © Greenwich Medical Media Ltd. ISSN 1047-9511