What is the characteristic of a 2nd degree AV block type 1?

• A. All P waves are conducted
• B. Some QRS complexes are dropped
• C. No P waves present
• D. Heart rate less than 60 bpm

Answer: (B)

A characteristic feature of a 2nd degree AV block type 1, also known as Mobitz type I or Wenckebach, is that some QRS complexes are indeed dropped. This occurs because there is a progressive lengthening of the PR interval until a QRS complex fails to be conducted.

In this type of block, every cycle there is a gradual increase in the length of time between the P wave and the QRS complex until a QRS complex is skipped or dropped entirely. This pattern distinguishes it from other types of heart blocks where conduction may not follow this progressive pattern.

The presence of all P waves being conducted is a characteristic of first-degree AV block, where there are no dropped beats. The absence of P waves suggests a more severe disruption in atrial to ventricular conduction, indicative of a complete heart block (3rd degree AV block). Heart rates less than 60 bpm can be observed in various conditions and are not specific to type 1 AV block.