In 2nd degree block type 2, what happens to the P waves?

In 2nd degree block type 2, the key characteristic is the occurrence of non-conducted QRS complexes. This means that while the P waves are consistently present, some of them do not lead to a corresponding QRS complex. In this type of block, the atrial impulses (P waves) are generated at a constant rate, but there is a failure to transmit some of these impulses to the ventricles, resulting in intermittently missed beats.

This pattern distinguishes type 2 from other AV block types, particularly because the relationship between the P waves and QRS complexes remains more stable compared to type 1, where the PR interval progressively lengthens before a QRS is dropped. In contrast, in type 2 block, the PR interval is generally constant when conduction does occur, which underscores the intermittent nature of the dropped QRS complexes without leading to a varying or absent P wave presence. Thus, the features of block type 2 illustrate a critical understanding of conduction abnormalities within the cardiac rhythm.