Cardiac Morphology and Nomenclature

Sequential Segmental Analysis: General Philosophy

To be able to diagnose the simplest communication between the atria or the most complex of malformations, the sequential segmental approach (also known as the European approach due to the promoters of the original concepts) as described here requires that normality be proven rather than assumed. Thus the patient with an isolated atrial septal defect in the setting of a normally constructed heart undergoes the same rigorous analysis as the patient with congenitally corrected transposition associated with multiple intracardiac defects.

Any heart can be considered in three segments: the atrial chambers, the ventricular mass, and the great arteries ( Fig. 3.1 ). By examining the arrangement of the component parts of the heart and their interconnections, each case is described in a sequential manner. There are limited possibilities for the arrangement of the individual chambers or arteries that make up the three segments. Equally, there are limited ways in which the chambers and arteries can be related to one another. The approach begins by examining the position of the atrial chambers. Thereafter, the atrioventricular (AV) junction and the ventriculoarterial junctions are analyzed in terms of connections and relations. Once the segmental anatomy of any heart has been determined, it can then be examined for associated malformations; these need to be listed in full. The examination is completed by describing the cardiac position and relationship to other thoracic structures. The segmental combinations provide the framework for building the complete picture because in most cases the associated lesions produce the hemodynamic derangement.

The philosophy of segmental analysis is founded on the morphologic method ( Box 3.1 ). Thus chambers are recognized according to their morphology rather than their position. In the normally structured heart, the right-sided atrium is the systemic venous atrium, but this is not always the case in the malformed heart. Indeed, the very essence of some cardiac malformations is that the chambers are not in their anticipated locations. It is also a fact of normal cardiac anatomy that the right-sided heart chambers are not precisely right sided; nor are the left chambers completely left sided ( Fig. 3.2 ). Each chamber has intrinsic features that allow it to be described as “morphologically right” or “morphologically left,” irrespective of location or distortion by the malformation. Features selected as criteria are those parts that are most universally present even when the hearts are malformed. In this regard, venous connections, for example, are not chosen as arbiters of rightness or leftness of atrial morphology. The atrial appendages are more reliable for identification. In practice, not all criteria for all the chambers can be identified in the living patient with a malformed heart. In some cases there may be only one characteristic feature for a chamber, and in a few cases rightness or leftness can be determined only by inference. Nevertheless, once the identities of the chambers are known, the connections of the segments can be established. Although spatial relationships—or relations—between adjacent chambers are relevant, they are secondary to the diagnosis of abnormal chamber connections. After all, the connections, like plumbing, determine the flow through the heart, although patterns of flow are then modified by associated malformations and hemodynamic conditions. The caveat remains that valvular morphology in rare cases (eg, an imperforate valve) allows for description of the connection between chambers, although not in terms of flow until the imperforate valve is rendered patent surgically or by other means.