Patient Care Technician (PCT) AAH Practice Exam

What characterizes a 3rd degree AV block?

1. P waves are dependent on QRS complexes

2. QRS complexes are independent of P waves

3. Only P waves are present without QRS complexes

4. Heart rate exceeds 200 bpm

The correct answer is: QRS complexes are independent of P waves

In a third-degree AV block, also known as complete heart block, there is a complete dissociation between the atrial and ventricular electrical activity. This means that the electrical impulses generated in the atria (the P waves) and those conducted through the AV node to the ventricles (the QRS complexes) are independent of each other. The atria beat at their own intrinsic rate, while the ventricles may beat at a slower intrinsic rate, typically a junctional or escape rhythm. This lack of coordination is critical because it results in an ineffective heart rhythm, leading to potential hemodynamic instability. Therefore, the correct characterization of a third-degree AV block is that the QRS complexes are independent of the P waves, reflecting the complete lack of communication between the atria and the ventricles, resulting in the two chambers acting on their own. The different choices present varying scenarios, but they do not accurately depict the complete dissociation characteristic of a third-degree AV block, as the correct option does.