[Relationship between QRS transition zone and the interventricular septum: using CT scan].

The relationship between the QRS transition zone of the standard 12-lead ECG and interventricular septum was studied. The position and the angle to the horizontal line of the interventricular septum were evaluated with computed tomography (CT) and compared to the QRS transition zone. The subjects were 36 patients with no cardiovascular diseases. The patients were divided into 3 groups according to the position of QRS transition zone: V1-V2 (8 cases), V3-V4 (21 cases), and V5-V6 (7 cases). The interventricular septum on CT was directed to the anterior chest wall between V3 and V4 in all 3 groups. The mean value of the interventricular septal angle did not differ from group to group, 52.1 degrees for V1-V2 group, 49.8 degrees for V3-V4 group, 48.2 degrees for V5-V6. It was concluded that the direction of the interventricular septum was not one of the major determinants of the QRS transition zone in the standard 12-lead ECG.