In second degree heart block type 2 (Mobitz II), what is typically observed on an EKG?

In second degree heart block type 2, also known as Mobitz II, the hallmark characteristic observed on an EKG is the presence of consistent PR intervals followed by sudden dropped QRS complexes. This indicates that the atrial impulses are consistently conducted to the ventricles until one is blocked or fails to be conducted, resulting in the missing QRS.

This pattern differentiates Mobitz II from Mobitz I (Wenckebach), which is characterized by progressively lengthening PR intervals before a dropped QRS complex occurs. The absence of variation in the PR interval in Mobitz II suggests a more stable conduction through the AV node until an unexpected failure occurs, making it critical to monitor for potential progression to complete heart block.

Additionally, while widened QRS complexes may be associated with other conditions, they are not a defining feature of Mobitz II specifically. In fact, the QRS complexes can remain narrow. Thus, the ability to recognize the distinct pattern of dropped beats with consistent PR intervals is essential in identifying this particular heart block on an EKG.