What is a key feature of junctional rhythms?

A key feature of junctional rhythms is the absence or inversion of P waves. This occurs because the electrical impulse is originating from the atrioventricular junction rather than the sinoatrial node, which is responsible for normal atrial depolarization and the creation of P waves. In junctional rhythms, the impulse typically either does not stimulate the atria or does so in such a way that the P waves are not clearly visible or are inverted. This distinguishes junctional rhythms from other types of rhythms that maintain recognizable P waves.

In contrast, the other characteristics provided do not align with junctional rhythms. An accelerated heart rate above 150 bpm describes tachycardia rather than the typically slower rates seen in many junctional rhythms. Regular atrial flutter waves indicate atrial flutter, which is a distinct rhythm involving a rapid reentrant circuit in the atria, not a junctional rhythm. Extended pauses between beats are indicative of varying block types, not characteristic of junctional rhythms, which typically display regularity despite the absence of P waves. Thus, absence or inversion of P waves is the defining feature of junctional rhythms.