In a premature ventricular contraction (PVC), why is the QRS complex taller and deeper than normal?
During normal ventricular conduction
, the left and right ventricles depolarize simultaneously
. As a result, depolarization going toward the left ventricle is somewhat opposed by simultaneous depolarization
going toward right ventricle. Therefore, under normal conditions, the QRS is relatively small
A PVC originates in one ventricle which depolarizes before the other ventricle
, and therefore there is no simultaneous opposing depolarization from opposite sides
. Therefore, QRS is very large