The nature of the obstructive muscular bundles in double-chambered right ventricle

Objective: Our goal was to establish the morphologic nature of the obstruct ive muscular lesions in double-chambered right ventricle, Methods: We based our morphologic observations on 10 normal hearts and on the surgical findi ngs in 26 patients, aged 0.5 to 24 years, with a mean of 6.9 years (SD 5.8 years). In the normal hearts, we measured the distance from the pulmonary v alve to the apex of the right ventricle and from the takeoff of the moderat or band to the ventricular apex. From angiograms available in 20 patients, using the frontal view we then measured the distance from the pulmonary val ve to the apex of the right ventricle and from the midpoint of the obstruct ive lesion to the apex of the right ventricle, This permitted calculations of multiple ratios. Results: In the 10 normal hearts, the moderator band to ok origin at a mean ratio of 0.48 (SD 0.16) of the ventricular length. On t he basis of the angiographic findings, we identified 2 basic forms of doubl e-chambered right ventricle, In 9 patients, the obstructive muscular shelf was positioned low and diagonally across the apical component, with a mean ratio of 0.38 relative to the ventricular length (SD 0.02), In the other 11 patients, the obstructive shelf was high and horizontal, with a mean ratio of 0.27 (SD 0.02), The difference was statistically significant (P = .001) . Surgical repair was performed successfully in all 26 patients through a r ight ventriculotomy, Conclusions: Double-chambered right ventricle is the c onsequence of a high or low muscular division of the apical component of th e right ventricle. The abnormal muscular bundle probably represents accentu ated septoparietal trabeculations, rather than always being an abnormal mod erator band.