Relation between aortic arch hypoplasia of variable severity and central muscular ventricular septal defects: emphasis on associated left ventricular abnormalities.

Among 25 heart specimens with a central muscular ventricular septal defect (including 3 with the architecture of a spontaneously closed defect), only 6 (24 percent) had an aortic arch of normal size and configuration. Isthmus atresia was present in one case, isthmus hypoplasia in eight cases, local coarctation in six and a combination of isthmus hypoplasia and local coarctation in another four. A study of the left ventricular morphologic features of the 25 hearts revealed the presence of a spectrum of additional anomalies. The aortic valve was bicuspid in 16 and mitral valve anomalies were present in 13 specimens. Mitral valve deformities present in the 13 specimens included congenital stenosis (5), deficient chordae tendineae (4), parachute valve (2), adherent valve leaflets (1) and a hypoplastic posteromedial papillary muscle (1). Furthermore, there was a large incidence of abnormal left ventricular muscular structures that could be classified into three basic types: (1) the anteroseptal "twist": thickening and deviation of the anterobasal septum and anterior wall, resulting in a relatively posterior position of the aortic ostium (16 cases); (2) a prominent anterolateral muscle (9 cases); and (3) a posteromedial muscle (9 cases). It is concluded that a central muscular ventricular septal defect is not an isolated malformation but is commonly part of a complex developmental anomaly. This complex of associated inflow and outflow tract lesions presumably may cause reduced aortic flow during morphogenesis, resulting in aortic arch hypoplasia of various degrees of severity.