The PR interval gradually lengthens in which condition?

The condition in which the PR interval gradually lengthens is known as 2nd degree AV heart block, specifically Type I, also referred to as Mobitz Type I or Wenckebach phenomenon. In this condition, there is a progressive prolongation of the PR interval on subsequent beats until a beat is dropped (a QRS complex is missing). This pattern creates a characteristic rhythm on the EKG, where you can see the PR interval getting longer consistently before the sequence resets itself.

The physiological mechanism behind this phenomenon is often due to increasing delay in conduction through the AV node. This gradual lengthening occurs because as each beat occurs, the conduction time through the AV node becomes longer for reasons such as heightened autonomic tone or structural abnormalities in the conduction system.

Understanding the behavior of the PR interval in different conduction disorders is crucial for accurate EKG interpretation, particularly as it relates to diagnosing heart block types. Identifying the specifics of how the PR interval changes can guide clinicians in deciding the appropriate management for the patient.