Which of the following characteristics is NOT associated with PAC?

The characteristic consistently associated with PAC, or Premature Atrial Contractions, does not include a consistently high heart rate. PACs typically occur as single premature beats in the atria and do not inherently affect the overall heart rate. While PACs can occur in a variety of scenarios, they do not cause a sustained increase in heart rate; rather, they may occur in a heart rate that is otherwise normal or occasionally elevated due to other factors.

In contrast, PACs are defined by the early occurrence of P waves, which appear prematurely in the rhythm. These P waves can often have different morphologies compared to sinus P waves, reflecting their atrial origin. The rhythm may also show variability in the PR interval, especially if the PAC is coupled with a normal sinus beat or if there is a varying conduction through the AV node. These characteristics are important in identifying PACs on an electrocardiogram.

The notion of an irregular rhythm is also common with PACs due to their nature of interrupting the regular sinus rhythm. However, the concept of having a consistently high heart rate does not align with the mechanics of PACs and is thus the correct choice for the characteristic that is NOT associated with them.