Effect of early activation sites knock-outs on the QRS. (Top) Clinical ECG of Group 3 patient (black). Changes in the activation sequence with different blocking combinations (left bundle branch block, posterior block, anterior block, and right bundle branch block). Activation maps in both ventricles are shown along with the specific simulated ECG (red), normal simulation (blue) in leads V1–V6. Black arrows represent lead of interest discussed in the text. ECG, electrocardiogram.