What is the characteristic EKG finding in First Degree Heart Block?

In First Degree Heart Block, the hallmark characteristic is a prolongation of the PR interval, which is measured from the beginning of the P wave to the beginning of the QRS complex. A PR interval that exceeds 200 milliseconds indicates a delay in the conduction through the atrioventricular (AV) node. This prolonged interval happens consistently with each heartbeat, thus distinguishing it from other types of heart block where there may be more significant interruptions in conduction.

The presence of a consistently prolonged PR interval greater than 120-200 ms underscores the diagnosis of First Degree Heart Block and is essential for recognizing this condition on an EKG. It is noteworthy that while the QRS duration may remain normal in First Degree Heart Block, the maintained conduction with a prolonged PR interval signals that the electrical signals are still reaching the ventricles adequately, albeit with some delay. This is why the other options do not accurately reflect the characteristic finding of First Degree Heart Block.