Discussion

The echocardiographic, angiographic, and MRI images of the two illustrative cases are that of a rare variant of apical ventricular septal defect, the left ventricular-infundibular apical ventricular septal defect. These are a group of muscular ventricular septal defects that share a unique set of features: a large ventricular apical septal defect at the left ventricle end opening into the infundibulo-apical recess of the right ventricle which is bound superiorly by the moderator band and separated from the rest of the right ventricle body by thick muscle bundles which may have intertrabecular recesses. ^{Reference Kumar, Lock and Geva1} Tsang et al. have attributed this particular character of the apical ventricular septal defect to incomplete compaction of the apical trabecular septum. ^{Reference Tsang, Hsia, Yates and Anderson3} An important concept for understanding this entity is knowledge of the presence of two apices in the right ventricle: the inflow or sinus apex (posterior) to which the tensor part of the tricuspid valve is attached and the infundibular apex (anterior) which is related to the parietal band, the conal septum, septal band, and the moderator band. ^{Reference Van Praagh, Mayer, Berman, Flanagan, Geva and Van Praagh2} The infundibulo-apical recess is located anterosuperior and leftward of the apex of the right ventricle inflow sinus. This recess extends to connect with the infundibulum of Right ventricular outflow tract, as demonstrated in the angiogram of case 2. Large apical ventricular septal defects that open beneath the moderator band into the right ventricle will open into this recess.

Spontaneous closure has been described in some of these defects ^{Reference Kumar, Lock and Geva1} (as in our case 1), and small defects with insignificant shunt maybe followed up. Interventional closure has been described as a feasible and safe option, and the device can be placed at the true ventricular septal defect at the left ventricle septum. ^{Reference Kumar, Lock and Geva1} Alternatively, the device can be deployed at the exit of the infundibulo-apical recess at the right ventricle end ^{Reference Kumar, Lock and Geva1} (where the device is placed across the moderator band as in case 2), in which case the recess becomes part of the left ventricle. This may result in loss of right ventricle volume and right ventricle dysfunction later if the infundibulo-apical recess formed a substantial proportion of the right ventricle apex. Surgical closure can be done by right ventricle infundibulotomy ^{Reference Van Praagh, Mayer, Berman, Flanagan, Geva and Van Praagh2–Reference Myhre, Duncan and Mee4} (incision placed over the infundibulo-apical recess, to the right of the anterior descending artery) and closing the ventricular septal defect with a patch. Care must be taken to close the true ventricular septal defect and avoid placing the patch at the right ventricle exit of the ventricular septal defect. Our second patient had loss of right ventricle volume due to exclusion of the right ventricle infundibular apex from the rest of the right ventricle. This may have led to the right ventricle diastolic dysfunction and subsequent right to left shunting across the patent oval foramen noted in him on follow-up. The right ventricle outpouchings noted in the follow-up angiogram and the bald appearance of the body of the right ventricle may point to an additional myopathic involvement (though MRI did not substantiate this), that has been described in some cases with large apicoinfundibular defects. The incorporation of the infundibulo-apical recess as part of left ventricle cavity acts as a large inert segment of the left ventricle, akin to an left ventricle apical aneurysm, and this could possibly be contributory to the mild left ventricle systolic dysfunction noted in our patient.