[Two-dimensional echocardiographic diagnosis of tetralogy of Fallot with a total conus defect]

Tetralogy of Fallot (TOF) with a total conus defect has some characteristics different from classical TOF in respect to its morphogenesis and clinical features. This anomaly, although rare in Europe, constitutes approximately 10% of all types of TOF in Japan. In this report, we studied 30 cases of TOF with angiographic or surgical documentation in order to investigate two-dimensional echocardiography as a possible mean of detecting a conus defect in TOF. We classified the entire group into three types according to the location of a ventricular septal defect (VSD): subpulmonic VSD (six cases, I), infundibular muscular VSD (11 cases, II) and perimembranous VSD (13 cases, III). A long-axis view along the right ventricular outflow tract rather than a short-axis view at the level of the aortic root was adopted as a useful examination for viewing VSDs. Using the former image, we could observe precisely a VSD just below the pulmonary valve in all six cases of Type I and three of Type II, but none of Type III. Three cases of Type II which had a short infundibular septum of several millimeters in length with surgical confirmation were very similar to cases of Type I. The discontinuity between the interventricular septum and the pulmonary valve was confirmed to be identical with subpulmonic VSD by angiographic and pathological studies. In conclusion, we could differentiate TOF with a total conus defect from the other types of TOF by detecting the echo defect in the septum just below the pulmonary valve with the aid of a long-axis view of the right ventricular outflow defect.