What type of heart block is associated with a prolonged PR interval followed by a dropped beat?

The type of heart block characterized by a prolonged PR interval followed by a dropped beat is indeed an example of a second-degree AV block, specifically Mobitz type I, also known as Wenckebach phenomenon. In this type of block, the conduction through the AV node progressively slows, resulting in an increasing PR interval until one impulse is not transmitted to the ventricles, leading to a dropped QRS complex.

This irregularity and pattern are significant because they highlight that while the heart is still conducting impulses, there is an intermittent failure to transmit impulses from the atria to the ventricles. This distinguishes it from first-degree AV block, where there is a consistent but prolonged PR interval without any dropped beats, as well as from third-degree AV block, where there is a complete dissociation between atrial and ventricular activity, showing no correlation between the PR intervals and ventricular beats.

Furthermore, bundle branch block does not directly relate to AV conduction; rather, it indicates a delay in the conduction through one of the bundle branches leading to issues with ventricular depolarization but does not manifest as a regular pattern of dropped beats like in second-degree AV block. Thus, the hallmark of the second-degree AV block is the presence of a prolonged PR interval that