The univentricular atrioventricular connection: Getting to the root of a thorny problem

Most hearts described as “single ventricle” or “univentricular heart” possess 2 ventricular chambers, even though 1 is usually described as an “outlet chamber.” This stems from the wide acceptance that the criterion of a single ventricle is the presence of a double-inlet atrioventricular (AV) connection. In recent years, using this criterion, an attempt was made to show how hearts with double-inlet right ventricle or “classic tricuspid atresia” were (in terms of ventricular morphology) just as univentricular as “single ventricle with outlet chamber.” This attempt brought still further confusion to an already contentious topic. The root of the problem clearly is the injudicious use of the adjective “single” or “univentricular.” Conventionally it is used to describe the ventricular mass. In most hearts with double-inlet connection it is not the ventricles that are univentricular; it is the AV connection. The concept of a univentricular AV connection, then, appropriately groups hearts with double-inlet along with those having absence of 1 AV connection. It distinguishes this entire group from those other hearts with biventricular AV connections (each atrium connected to its own ventricle). The term “univentricular AV connection” is thus a collective one for all those hearts in which the atria connect to only 1 ventricle. Confusion will be completely removed if individual hearts are described for what they are in terms of AV connection and ventricular morphology (for example, double-inlet left ventricle with rudimentary right ventricle rather than single ventricle with outlet chamber).