What characterizes a Mobitz block?

What characterizes a Mobitz block?

• A. A normal PQRST cycle followed by an irregular QRS complex
• B. A series of normal P waves without any QRS complexes
• C. A block that produces P waves not conducted through the AV node
• D. An irregularly timed QRS complex after each P wave

Answer: (C)

A Mobitz block is characterized by the presence of P waves that are not conducted through the AV node, leading to intermittent failure of QRS complexes. This occurs in the context of a second-degree heart block, where some impulses from the atria (P waves) are not transmitted to the ventricles, causing the QRS complexes to appear inconsistently.

In Mobitz type I (Wenckebach), the P waves are followed by progressively longer PR intervals until a QRS complex is dropped. In Mobitz type II, the PR intervals remain constant, but the QRS complexes are dropped at a regular interval. Both types reflect the behavior of P waves being generated but not resulting in ventricular contraction, particularly due to issues at the level of the AV node.

The other options describe scenarios that do not accurately capture the essential feature of a Mobitz block; for example, a normal PQRST cycle followed by an irregular QRS complex does not imply a block condition, and a series of normal P waves without any QRS complexes suggest a complete heart block rather than specifically a Mobitz type scenario. Furthermore, an irregularly timed QRS complex after each P wave describes a different rhythm disturbance.