What is a key feature of second degree heart block Mobitz type 2?

In second-degree heart block Mobitz type 2, one of the defining characteristics is the presence of constant PR intervals preceding the dropped QRS complexes. This means that each atrial impulse is conducted through the AV node to the ventricles without alteration in timing until the impulse is blocked, leading to a QRS complex not being produced.

The stability of the PR interval is a critical aspect that differentiates Mobitz type 2 from other types of heart block, such as Mobitz type 1 (Wenckebach), where the PR intervals progressively lengthen until a QRS complex is dropped. In Mobitz type 2, the regular and unchanged duration of the PR interval indicates that the conduction through the AV node is consistent just before the occurrence of a non-conducted beat. This clarity is crucial for clinicians in diagnosing and managing the condition appropriately.

Other factors, such as the independence of atrial and ventricular rates, can be associated with different cardiac conditions, but they do not exclusively define Mobitz type 2. The key aspect of a constant PR interval is what marks the signature pattern of this specific type of heart block.