Complete left bundle branch block

Delayed and abnormal activation of the left ventricular myocardium, and a diffuse slowing of conduction throughout the left ventricle leads to the following changes on the ECG: there is a tall monophasic and broadened R wave in leads I, aVL, and V6 instead of a septal Q wave; there is a QS complex which is abnormal and widened in V1 instead of a small initial R wave due to septal activation; the QRS interval is prolonged >0.12 seconds; myocardial repolarization changes including T wave inversion and ST segment depression are evident.