What condition could lead to a prolonged PR interval on an EKG?

A prolonged PR interval on an EKG is indicative of first-degree heart block, which is characterized by a delay in the conduction through the atrioventricular (AV) node. In this condition, each atrial impulse still reaches the ventricles, but there is a consistent slowing of conduction time, resulting in a PR interval greater than 200 milliseconds. This alteration is often seen in patients with increased vagal tone, medications affecting AV conduction, or in some underlying heart conditions.

Other conditions listed, such as atrial fibrillation, typically do not present with a prolonged PR interval, as they involve irregular and often rapid electrical activity that does not result in a consistent PR interval measurement. Bundle branch block primarily affects the QRS complex rather than the PR interval and does not directly cause PR interval prolongation. Tachycardia can lead to a variety of EKG changes, but it does not specifically involve prolonged PR intervals as a defining characteristic. Thus, identifying first-degree heart block is essential for understanding the significance of a prolonged PR interval on an EKG.