Answer 13

13.  Choice A is the correct answer.  Normally both ventricle depolarize to the ventricles at the same time.  When there is a bundle branch block, there is a delay in the stimulus which leads to the widened QRS complex with the classic R and R' waves.  With a right bundle branch block, lead V1 and V2 are the closest to the right ventricle and that is where you see the changes.  With a left bundle branch block leads V5 and V6 are the closest to the left ventricle, and the changes to the QRS complex occur with these leads.  With lateral ischemia, you see T wave inversion or ST depression in leads I, avL, V5 or V6.  With premature ventricular contractions, you just see an isolated widened QRS complex occurring earlier in the cycle with a compensatory pause.