What does a 3rd Degree AV Block indicate about the relationship between P waves and QRS complexes?

A third-degree AV block, also known as complete heart block, signifies a complete dissociation between the atria and ventricles. In this condition, the electrical impulses originating from the atria (which create P waves) do not reach the ventricles, resulting in an absence of a consistent relationship between P waves and QRS complexes.

As a result, the P waves may occur at their own intrinsic rate, while the QRS complexes also generate independently, each at their own rate. This lack of coordination highlights that, while both P waves and QRS complexes can be observed on the ECG, they do not follow a predictable pattern relative to one another, thus confirming that there is no consistent relationship. This is critical for recognizing the serious implications of third-degree AV block, as it can lead to hemodynamic instability due to ineffective ventricular contractions.