Over the years, so-called univentricular hearts represented one of the greatest challenges for surgical correction. All this changed with the advent of the Fontan procedure,1 along with the realization that it could become the final stage of the sequence of procedures used to correct lesions such as those included in the hypoplastic left heart syndrome,2 which previously had been beyond surgical repair. The overall group of lesions also posed significant problems in adequate description and categorization. Even these days, many continue to describe patients with a double inlet left ventricle as having a single ventricle, despite the fact that, with the availability of clinical diagnostic techniques producing three-dimensional datasets, patients with this lesion can be seen to have two chambers within their ventricular mass, one being large and the other small (Figure 9.1.1). The semantic problems with description can now be resolved by the simple expedient of describing the patients as having functionally univentricular hearts.3

Understanding the anatomy of septal defects is greatly facilitated if the heart is thought of as having three distinct septal structures: the atrial septum, the atrioventricular septum, and the ventricular septum (Figure 8.1.1). The normal atrial septum is relatively small. It is made up, for the most part, by the floor of the oval fossa. When viewed from the right atrial aspect, the fossa has a floor, surrounded by rims. As we have shown in Chapter 2, the floor is derived from the primary atrial septum, or septum primum. Although often considered to represent a secondary septum, or septum secundum, the larger parts of the rims, specifically the superior, antero-superior, and posterior components, are formed by infoldings of the adjacent right and left atrial walls.1 Infero-anteriorly, in contrast, the rim of the fossa is a true muscular septum (Figure 8.1.2).

Cardiac surgeons, like paediatric cardiologists, consider that knowledge of cardiac development, and morphogenesis, is a major aid to the understanding of the anatomy of both the normal and the congenitally malformed heart. In previous editions of our textbook, we have eschewed the option of including a chapter on development. We had taken the stance that, until recently, accounts of the complex changes occurring during cardiac development were based on speculations, rather than evidence. Since the turn of the century, all that has changed. Evidence now exists not only to underpin accurate descriptions of the changes in morphology that occur during development, but also to reveal the lineages and molecular biology of the multiple tissues found in the definitive structures.1 In this chapter, however, we will confine ourselves to description of the key morphological features of cardiac development.

It is axiomatic that a thorough knowledge of valvar anatomy is a prerequisite for successful surgery, be it valvar replacement or reconstruction. The surgeon will also require a firm understanding of the arrangement of other aspects of cardiac anatomy to ensure safe access to a diseased valve or valves. These features were described in the previous chapter. Knowledge of the surgical anatomy of the valves themselves, however, must be founded on appreciation of their component parts, the relationships of the individual valves to each other, and their relationships to the chambers and arterial trunks within which they reside. This requires understanding of, first, the basic orientation of the cardiac valves, emphasizing the intrinsic features that make each valve distinct from the others. Such information must then be supplemented by attention to their relationships with other structures that the surgeon must avoid, notably the conduction tissues and the major channels of the coronary circulation.

The surgical problems posed by cardiac malformations may be considerably increased when the heart itself is in an abnormal position. This is, in part, due to the unusual anatomical perspective presented to the surgeon because of the malposition, and also to the abnormal locations of the cardiac chambers, which may necessitate approaches other than those already discussed. Cardiac malposition in itself, nonetheless, does not constitute a diagnosis. Any normal or abnormal segmental combination can be found in a heart which itself is abnormally located. The heart may be normal, despite its abnormal location, but extremely complex anomalies are frequently present. Consequently, the very presence of an abnormal cardiac position emphasizes the need for a full and detailed segmental analysis of the heart. All the rules enunciated in Chapter 7 apply should the heart not be in its anticipated position.

Systems for describing congenital cardiac malformations have frequently been based on embryological concepts and theories. As useful as these systems have been, they have often had the effect of confusing the clinician, rather than clarifying the basic anatomy of a given lesion. As far as the surgeon is concerned, the essence of a particular malformation lies not in its presumed morphogenesis, but in the underlying anatomy. An effective system for describing this anatomy must be based on the morphology as it is observed. At the same time, it must be capable of accounting for all congenital cardiac conditions, even those that, as yet, might not have been encountered. To be useful clinically, the system must be not only broad and accurate, but also clear and consistent. The terminology used, therefore, should be unambiguous. It should be as simple as possible. The sequential segmental approach provides such a system.1

The coronary circulation consists of the coronary arteries and veins, together with the lymphatics of the heart. Since the lymphatics, apart from the thoracic duct, are of very limited significance to operative anatomy, they will not be discussed at any length in this chapter. The veins, relatively speaking, are similarly of less interest. In this chapter, therefore, we concentrate on those anatomical aspects of arterial distribution that are pertinent to the surgeon, limiting ourselves to brief discussions of the cardiac venous drainage and the cardiac lymphatics.

When we describe the heart in this chapter, and in subsequent chapters, our account will be based on the organ as viewed in its anatomical position.1 Where appropriate, the heart will be illustrated as it would be viewed by the surgeon during an operative procedure, irrespective of whether the pictures are taken in the operating room, or are photographs of autopsied hearts. When we show an illustration in non-surgical orientation, this will be clearly stated.

In the normal individual, the heart lies in the mediastinum, with two-thirds of its bulk to the left of the midline (Figure 1.1). The surgeon can approach the heart, and the great vessels, either laterally through the thoracic cavity, or directly through the mediastinum anteriorly. To make such approaches safely, knowledge is required of the salient anatomical features of the chest wall, and of the vessels and the nerves that course through the mediastinum (Figure 1.2).

Regardless of the surgical approach, once having entered the mediastinum, the surgeon will be confronted by the heart enclosed in its pericardial sac. In the strict anatomical sense, this sac has two layers, one fibrous and the other serous. From a practical point of view, the pericardium is essentially the tough fibrous layer, since the serous component forms the lining of the fibrous sac, and is reflected back onto the surface of the heart as the epicardium. It is the fibrous sac, therefore, which encloses the mass of the heart. By virtue of its own attachments to the diaphragm, it helps support the heart within the mediastinum. Free-standing around the atrial chambers and the ventricles, the sac becomes adherent to the adventitial coverings of the great arteries and veins at their entrances to and exits from it, these attachments closing the pericardial cavity.1

The disposition of the conduction system in the normal heart has already been emphasized (see Chapter 2). In that earlier chapter, we pointed to the importance, during surgical procedures, of avoiding the cardiac nodes and ventricular bundle branches, and scrupulously protecting the vascular supply to these structures. In this chapter, we will consider the anatomy of these tissues relative to the treatment of intractable problems of cardiac rhythm, specifically the normal and abnormal atrioventricular conduction axis. The abnormal dispositions of the conduction tissues to be found in congenitally malformed hearts, features of obvious significance to the congenital cardiac surgeon, will be discussed in the sections devoted to those lesions in the chapters that follow. In this chapter, nonetheless, we will also discuss surgical procedures performed to treat arrhythmias that develop in the setting of the Fontan circulation.