What indicates an increase in PR interval on an EKG?

An increase in the PR interval on an EKG represents a delay in the conduction of electrical impulses from the atria to the ventricles through the AV node. The PR interval is the time taken for the electrical impulse to travel from the atrial contraction to the beginning of ventricular contraction. A longer PR interval indicates that this conduction time is prolonged, which can be associated with conditions such as AV block.

While the other choices may have relevance in the context of an EKG, they do not relate directly to the definition of the PR interval. A shortened QRS complex reflects the time taken for ventricles to depolarize and is not synonymous with the PR interval. A prolonged QT interval pertains to the time of ventricular repolarization and does not affect the PR interval directly. Flat T waves can indicate various cardiac conditions but are not indicative of the PR interval length.

Thus, a longer PRI clearly signifies a delay in atrioventricular conduction, making it the correct choice for indicating an increase in the PR interval on an EKG.