Abnormally the slow depolarization of the ventricles would most likely change the shape of the QRS in an ECG tracing. It is a combination of three graphical deflections which is seen on a typical electrocardiogram. It is the most visually obvious and central part of the tracing. It corresponds to depolarization of left and right ventricles of the human heart.
During the activity, it may be shorter in children.
QRS waves occur in succession rapidly. Q wave is a downward deflection following P wave. R wave follows upward deflection and S wave is downward deflection which is after R wave while T wave follows S waves.