Andersons pediatric cardiology 1816

FIG 69.22 Combinations of the sidedness of the straddling atrioventricular (AV) valve (columns) and the right-sided as opposed to leftsided ventricular topology (rows) that can be found when there is absence of one AV connection but the solitary AV valve is straddling and overriding These combinations produce AV connections that are uniatrial but biventricular In such instances, both ventricles will be incomplete to a greater or lesser extent, but one of them is usually dominant Unbalanced Atrioventricular Septal Defect The spectrum of malformation described for straddling and overriding of either the mitral or tricuspid valves can be replicated in the setting of a common atrioventricular valve It is sometimes thought, furthermore, that the straddling solitary valve is a “common” entity This, of course, cannot be the case, since the solitary straddling valve guards either the right or the left atrioventricular junction For the valve to be common, it must guard the entirety of both atrioventricular junctions Such common valves, as found in atrioventricular septal defect with common atrioventricular junction, usually straddle the crest of the ventricular septum, with their bridging leaflets supported by tendinous cords in both ventricles However, in some hearts with double-inlet ventricle, a common atrioventricular valve can be exclusively supported by either the dominant right (see Fig 69.18B) or the dominant left ventricle The degree of overriding of the common valve produces the spectrum of unbalanced atrioventricular septal defects The common valve being exclusively committed to one or other ventricle can be considered to represent the extreme form of atrioventricular septal defect with a common atrioventricular junction Determining the extent of overriding, and hence the relative size of the two ventricles, remains one of the most difficult tasks for the pediatric cardiologist This is because it is the size of the incomplete ventricle, particularly in the setting of right ventricular dominance, that determines the options for biventricular as opposed to functionally univentricular repair These problems, and the underlying anatomic situations, are discussed in Chapter 32 Complex Double-Outlet Ventricle As discussed at length in Chapter 39, surgical repair of double-outlet ventricle depends on tunneling the interventricular communication to one or other of the ventricular outflow tracts This is usually possible when the communication is in subaortic, subpulmonary, or doubly committed locations It can frequently be achieved even when, at first sight, the communication may seem to be in a noncommitted position However, in other circumstances, features such as anomalous attachment of the tension apparatus of the atrioventricular valves may conspire as to render impossible the construction of an interventricular tunnel This is also likely to be the case when the interventricular communication is within the apical component of the muscular septum or opens to the inlet of the right ventricle These circumstances are again likely to tilt the balance of surgical repair in favor of construction of the Fontan circulation The anatomic features underscoring these decisions are discussed in Chapter 40  ... Determining the extent of overriding, and hence the relative size of the two ventricles, remains one of the most difficult tasks for the pediatric cardiologist This is because it is the size of the incomplete ventricle, particularly in the