What is a defining feature of 2nd degree AV block Type 2?

The defining feature of 2nd degree AV block Type 2 is the presence of a constant PR interval that is consistent with every P wave, accompanied by the occasional dropping of QRS complexes. In this type of block, the rhythm remains regular until a QRS complex is dropped, after which the pattern continues with the same PR interval. This characteristic distinguishes it from other types of AV blocks where the PR interval may change or where there is an irregular rhythm.

In contrast, a regular rhythm with varying QRS would suggest a different type of arrhythmia and is not applicable here. The option indicating regular P waves with no QRS describes a more severe type of block, such as in complete heart block, rather than 2nd degree AV block Type 2. An irregular rhythm is more indicative of a higher degree of block or other arrhythmias, such as atrial fibrillation. Thus, the constant PR interval with the selective dropping of QRS complexes accurately encapsulates the hallmark features of 2nd degree AV block Type 2.