Which type of second-degree atrioventricular block involves progressive lengthening of AV conduction times until a P wave is not conducted?

The characteristic of a second-degree atrioventricular block that involves progressive lengthening of the conduction time until a P wave is not conducted describes Type 1, also known as Mobitz Type I or Wenckebach. In this type of block, there is a gradual prolongation of the PR interval with each successive beat until one P wave is blocked, resulting in a missed QRS complex. The pattern typically resets after the dropped beat, where the sequence begins anew with a normal PR interval.

This progressive increase in the PR interval is a hallmark of this block and helps clinicians differentiate it from other types of AV blocks. Understanding this pattern is crucial for identifying the specific type of second-degree AV block and managing it appropriately, as treatment decisions may vary based on the type and symptoms presented by the patient.