Final answer:
The QRS complexes on an EKG are used to determine the regularity of the ventricular rate, as they represent the moment when the ventricles begin to contract.
Step-by-step explanation:
An EKG technician should use the QRS complexes to determine the regularity of the ventricular rate. The QRS complex represents the depolarization of the ventricles, marking the moment the ventricles begin to contract. This is crucial in assessing the regularity of the ventricular contractions. The P wave represents the depolarization of the atria and is not used to measure the ventricular rate. The T wave indicates ventricular repolarization and is also not used for assessing ventricular contraction regularity. Similarly, the U wave is related to the repolarization of the Purkinje fibers and is not a main factor in determining the regularity of ventricular rate. Therefore, to measure the regularity of ventricular contractions, QRS complexes are the key component to observe.