As mentioned earlier, right bundle branch block is characterized as being incomplete or complete. Incomplete RBBB has the same ECG characteristics as complete RBBB except that the terminal right ventricular forces are less prolonged and the total QRS duration is between 0.10 and 0.12 seconds rather than equal to or greater than 0.12 seconds. The ECG shown here is from a 42 year old woman with an atrial septal defect. The ECG shows incomplete RBBB with a total QRS duration of 0.11 seconds. The delayed unopposed rightward and anteriorly directed right ventricular forces are represented by the S waves in leads I, aVL and V3-V6, and by the R’ waves in leads aVR and V1.