Final answer:
With Third-Degree AV Block, there is complete dissociation between P waves and QRS complexes, meaning the atria and ventricles beat independently, and the impulses from the SA node do not pass through the AV node to the ventricles.
Step-by-step explanation:
In the case of a patient's ECG revealing a Third-Degree AV Block (complete heart block), what can be expected is B) Complete dissociation between P waves and QRS complexes. In Third-Degree AV Block, there is a lack of correlation between atrial activity (P waves) and ventricular activity (QRS complexes), which means the atria and ventricles beat independently of each other. The other options A) Normal PR interval, C) Regular atrioventricular conduction, and D) Shortened QT interval are not characteristic of Third-Degree AV Block. With complete heart block, some impulses initiated by the SA node do not reach the AV node at all. As a result, the P waves on an ECG are not followed by QRS complexes, indicating a total blockage of the electrical impulse at the AV node level.