What is a characteristic of premature junctional contractions?

Premature junctional contractions (PJCs) are a type of ectopic beat that originates from the junctional tissue of the heart, which is located between the atria and ventricles. One of the defining characteristics of PJCs is the presence of an inverted P wave on an electrocardiogram (ECG) or the absence of a P wave altogether. This occurs because the electrical impulse initiating the contraction arises from the junctional area, which is typically not part of the normal atrial depolarization pathway. When the impulse is conducted backward toward the atria, it can result in an inverted P wave if it is visible on the ECG.

In some cases, the P wave may completely be absent, as the junctional beats can occur before the atrial depolarization takes place. However, the characteristic of an inverted P wave is the most directly associated with premature junctional contractions compared to the other characteristics listed, making it the correct choice in this context. The appearance of an inverted P wave is an important diagnostic clue when analyzing rhythm disturbances in telemetry and cardiac assessments.