Echocardiographic and morphological correlations in tetralogy of Fallot

Our aim was to clarify the location and structure of the outlet septum relative to the free-standing subpulmonary infundibulum in the setting of tetralogy of Fallot and to examine its relationship to the other components of the subpulmonary outflow tract, determining their potential influence on clinical outcome.

We studied prospectively 41 patients with tetralogy of Fallot (mean age 14 +/- 10.9 months) prior to surgical repair, and compared them with 15 patients undergoing closure of a ventricular septal defect associated with malalignment of the outlet septum but no subpulmonary infundibular stenosis (Eisenmenger ventricular septal defect), and 20 healthy controls. We also examined available autopsied hearts from cases with uncorrected tetralogy of Fallot (8) and Eisenmenger ventricular septal defect (13). Data were indexed for body surface area, and diameter of the tricuspid valve, respectively. The overall length of the subpulmonary infundibulum, including the extent of the muscular outlet septum, was significantly greater for patients with tetralogy of Fallot compared to normals (2.34 +/- 0.6 vs 1.46 +/- 0.34 cm/BSA0.5, P<0.001), whereas the difference between those with tetralogy of Fallot and an Eisenmenger ventricular septal defect was confined to the degree of narrowing of the subpulmonary outlet (0.43 +/- 0.22 vs 2.17 +/- 0.64 cm/BSA0.5, P<0.001). Within the tetralogy of Fallot group, there were linear relationships between deviation of the outlet septum (r= -0.61, P<0.005) and the diameter of the pulmonary valvar orifice (r=0.75, P<0.001), suggesting that growth of the pulmonary arteries may be related to this feature. When patients requiring a transannular patch as part of their surgical repair were compared with those not needing this procedure, differences were found in the diameter of the pulmonary valvar orifice and the pulmonary trunk, but not in the dimensions of the outlet septum.

The position of the outlet septum in relationship to the remainder of the muscular subpulmonary infundibulum represents a hallmark of tetralogy of Fallot, permitting its differentiation from Eisenmenger ventricular septal defects and normal hearts.