Barron/Elsevier Critical Care Registered Nurse (CCRN) practice test

A third-degree AV heart block indicates a total failure of conduction between the atria and ventricles, leading to the atria and ventricles contracting independently. If the block occurs above the bundle of His, the escape rhythm that emerges typically originates from the junctional tissue, which can take over as a pacemaker due to the lack of signals reaching the ventricles from the atria.

In this scenario, the junctional escape rhythm occurs as the heart tries to maintain a minimum heart rate. The junctional rhythm is characterized by a regular rhythm with a rate that typically falls between 40-60 beats per minute, depending on whether the escape is occurring from a higher or lower junctional focus. This makes junctional escape the appropriate choice, as it reflects the heart's adaptation to maintain cardiac output despite the blocked conduction through the AV node.

This understanding of the relationship between the site of the block and the type of rhythm that emerges is crucial in critical care, as it helps guide treatment and management of arrhythmias in patients experiencing advanced heart blocks.