The Two-Chambered Right Ventricle

THE DIVISION of the right ventricle into two chambers by aberrant, hypertrophied muscular bands is a relatively rare congenital cardiac malformation. No reports have been found that describe the details of anatomic structure and hemodynamics in this anomaly, although Keith, Rowe, and Vlad' and Kjellberg et al.2 alluded to this malformation in their texts. Grant, Downey, and MacMahon3 described the architecture of the complex intrinsic bulbar musculature of the right ventricle, and stated "If the oblique component (cf. the bulbar musculature) is hypertrophied, the obstruction will lie much lower in the outflow tract, adjacent to the moderator band." The two-chambered right ventricle is usually seen in association with an interventricular septal defect, and the hypertrophied muscular bands produce an effective stenosis with an inflow high-pressure chamber immediately below the tricuspid valve and a low-pressure outflow chamber distal to the bands. This malformation should not be classified as tetralogy of Fallot, because the anatomic structure is quite different (fig. 1). Nine patients have been found with this abnormality during the past 5 years (1956 to 1961) among 600 infants and children who had diagnostic cardiac studies at the St. Louis Children's Hospital. The purpose of this report is to show that (1) this anomaly may be mistakenly diagnosed as acyanotic tetralogy of Fallot or isolated interventricular septal defect, (2) the diagnosis can be made with the aid of selective angiocardiography, and (3) this cardiac malformation is amenable to surgical correction.