What is the term for an event within a rhythm where the R to R interval is irregular due to early beats?

The term that describes an event within a rhythm where the R to R interval is irregular due to early beats is a premature junctional contraction (PJC). PJCs occur when an ectopic focus in the junctional area—between the atria and ventricles—fires earlier than expected, interrupting the regular rhythm. This results in an early beat, which causes the subsequent R to R interval to be shorter than usual, leading to the irregularity in the rhythm. This occurrence is significant because it indicates that there is a disruption in the normal pacing dynamics of the heart, which can be brought on by various factors such as increased sympathetic tone or ischemia.

The other terms do not accurately reflect the scenario described in the question. A P wave Junctional Complex does not pertain specifically to irregularities caused by early beats; rather, it suggests the presence of a junctional rhythm where the atrial activity is influenced by junctional pacing. A Junctional Escape Beat is a late beat that occurs when the primary pacemaker fails, and it does not specifically indicate early rhythm disturbances. A Conduction Block generally refers to a complete obstruction in the heart's electrical conduction pathways, leading to systematic rhythm issues, but not specifically to the occurrence of early beats.