When evaluating the PR interval, what characteristic indicates a 2nd degree type 2 block?

In the context of heart block classification, a 2nd degree type 2 block, also known as Mobitz type II, is characterized by a regular PR interval. This is an important distinguishing feature because, in contrast to 2nd degree type 1 (Mobitz type I), where the PR interval progressively lengthens until a QRS complex is dropped, the PR interval in type II remains constant and does not vary.

This consistency in the PR interval occurs even though there may be dropped beats. The regularity allows healthcare providers to identify the block and inform their clinical approach, particularly of mobilization or management of potential bradycardia associated with this heart block. The regular pattern of the PR interval is a key characteristic that aids in distinguishing this block from other types of heart conduction abnormalities.