Final answer:
An EKG technician should measure the P wave to evaluate for atrial depolarization, which is the trigger for atrial contraction. The P wave comes before the QRS complex, which signifies ventricular depolarization, and the T wave, which indicates ventricular repolarization.
Step-by-step explanation:
To evaluate for atrial depolarization, an EKG technician should measure the P wave. The P wave on an ECG represents the depolarization of the atria, which is the process that triggers the atria to contract and pump blood into the ventricles. This occurs before the QRS complex, which signifies ventricular depolarization, followed by the T wave, which represents ventricular repolarization. Notably, atrial repolarization happens during the QRS complex and is therefore not visible on an ECG because it is masked by the stronger electrical activity of the ventricles.