What is a key characteristic of a premature ventricular contraction (PVC)?

A key characteristic of a premature ventricular contraction (PVC) is the absence of a P wave and the presence of a wide QRS complex. This is indicative of the fact that PVCs originate from the ventricles rather than the atria, which is why you do not see an associated P wave preceding the QRS complex. The wide QRS complex is attributed to the abnormal conduction pattern that occurs when the ventricles are activated prematurely. This can happen because the electrical impulse does not conduct through the normal pathways of the heart's conduction system, resulting in slower depolarization and a wide QRS appearance.

In contrast, scenarios where there is a narrow QRS complex would typically suggest that the impulse originates from above the ventricles (such as the atria or AV node), which wouldn't align with the definition of a PVC. Normal P waves indicate there is atrial depolarization occurring as per usual conduction, which does not happen in PVCs. The absence of the P wave and the altered shape of the QRS complex are critical markers used by healthcare professionals to identify PVCs on an electrocardiogram.