For some insight, the electrical signal (P wave) moves from the heart's upper chambers (the atria) to the lower chambers (the ventricles), it causes the heart to beat. For the heart to beat properly, the timing of the electrical signal is important.
A short P wave could indicate a extra pathway or short-cut pathway for the P wave and may arrive at the ventricles too soon. Could cause arrhythmia (rhythm disorder)...worst case scenario. All EKG readings require support from othe clinical evidence.