What rhythm features a PR interval that varies from beat to beat, indicating no conduction between the SA node and the ventricle?

The rhythm that features a PR interval that varies from beat to beat, indicating no conduction between the SA node and the ventricle, is third-degree AV block. In this condition, there is a complete dissociation between the atrial and ventricular activities. The atria may contract and generate impulses from the SA node, but these impulses do not reach the ventricles due to a complete block at the AV node. As a result, the PR interval is not consistent because the atrial and ventricular rhythms are independent of one another; atrial contractions occur at one rate, and ventricular contractions occur at another.

In contrast, a second-degree AV block would typically show some conduction between the atria and ventricles, with certain beats failing to conduct but still maintaining some regularity in the PR intervals until a dropped beat occurs. A junctional rhythm is characterized by the absence of atrial activity with ventricular escape beats, and it has a regular rhythm without variability in the PR interval. Multifocal atrial tachycardia is characterized by varying P waves with different morphologies and does not exhibit the complete dissociation present in third-degree AV block. Thus, the defining feature of varied PR intervals due to a block at the AV node aligns exclusively with third