What is the name for a P wave that results from impulses that originate outside the SA node?

A P wave that results from impulses generated outside the SA node is referred to as a P prime. This typically indicates that atrial depolarization is initiated by a source other than the sinoatrial (SA) node, which is the primary pacemaker of the heart. The presence of a P prime can suggest that there is an ectopic atrial focus responsible for initiating the cardiac cycle rather than the SA node.

In contrast, terms such as Q prime, R wave, and T wave refer to different components of the EKG waveforms. The Q wave is part of the QRS complex and denotes the first negative deflection. The R wave is the first positive deflection following the P wave and corresponds to ventricular depolarization. Meanwhile, the T wave reflects ventricular repolarization. Each of these has distinct roles in the EKG representation of the heart's electrical activity, making P prime the only appropriate term for a P wave originating outside the normal pacemaker site.