FIG 39.3 Double-outlet right ventricle with subaortic interventricular communication and pulmonary stenosis In both hearts, there is obstruction at the mouth of the subpulmonary infundibulum (bracket) The heart in panel A has bilateral infundibula, whereas the heart in panel B has fibrous continuity in the roof of the defect between the leaflets of the aortic and mitral valves In both hearts there is fibrous continuity posteroinferiorly between the leaflets of the mitral and tricuspid valves, making the defect perimembranous As shown in panel A, the defect opens to the right ventricle between the limbs of the septomarginal trabeculation (yellow bars) The specific morphology of the interventricular communication has major surgical significance When there is a muscular posteroinferior rim, the atrioventricular conduction axis is not directly related to the margins of the defect and is less vulnerable at operation In many cases the aortic valve retains part of its connection within the left ventricle As long as most of the aorta is supported by the right ventricle, it is appropriate to diagnose the ventriculoarterial connection as being double-outlet, remembering that commitment is assessed on the basis of the short axis of the overriding arterial root (Fig 39.4) Important associated lesions may include a restrictive interventricular communication, which in essence represents obstruction of the left ventricular outlet Mitral stenosis can also be found FIG 39.4 Short axis of the base of the ventricular mass as viewed from the cardiac apex in the setting of overriding of the aortic root When, as shown, the larger part of the circumference of the root (in green), is supported by the right ventricle when assessed relative to the chord subtended by the ventricular septum, the ventriculoarterial connection is justifiably considered to be diagnosed as double-outlet right ventricle It follows that it is the lesser part of the circumference (in yellow) that is supported by the left ventricle Subpulmonary Interventricular Communication These hearts are usually described as the Taussig-Bing malformation In the initial heart thus described, both arterial valves were supported by complete muscular infundibula The term is now used to describe the spectrum of overriding of the pulmonary trunk in the setting of parallel arterial trunks, with the ends of the spectrum being either double-outlet right ventricle (Fig 39.5) or discordant ventriculoarterial connections (see Chapter 37).13 The interventricular communication, again opening to the right ventricle between the limbs of the septomarginal trabeculation, does so beneath the pulmonary trunk, with the muscular outlet septum attached to the ventriculoinfundibular fold A muscular posteroinferior rim, formed by union of trabeculation and fold, often separates the rim of the defect itself from the membranous septum (see Fig 39.5A) As explained earlier, when present, the rim protects the atrioventricular conduction axis In most cases, nonetheless, the defect extends posteriorly, becoming perimembranous (see Fig 39.5B)