Angiographic classification of ventricular septal defects in tetralogy of Fallot

The ventricular septal defect (VSD) in Fallot's tetralogy (TF) was classified into four types: perimembranous (PM), muscular outlet (MO), doubly committed subarterial (DS), and DS with perimembranous extension. From July 1990 to June 1992, we used angiocardiography to define preoperatively the types of VSD in 30 cases of TF, and correlated them with the operative findings. The angiographic images used to identify the types of VSDs were anteroposterior (AP) plus cranial tilting 20-30 degrees, right anterior oblique 30 degrees plus cranial tilting 30 degrees (elongated RAO view) and true lateral view of right ventricular (RV) angiography. DS type and MO type had a shadow of muscle bar postero-inferiorly in the AP and elongated RAO views, while perimembranous type and MO superiorly in the lateral view. DS with perimembranous extension type was devoid of both shadows. The results revealed 73% accuracy rate of prediction by angiocardiography. Most of the incorrectly predicted cases were attributed to a tiny inferior muscle bar in MO type and was mistaken as pm type VSD. We conclude that routine RV angiography before correction of tetralogy of Fallot to identify the types of VSDs is feasible. This information facilitates planning of surgical strategy.