Final answer:
The correct answer is D. A QRS interval > 0.10 seconds usually indicates an atrioventricular block, representing an issue with the conduction of electrical signals in the heart. Specifically, it can suggest either a second or third-degree block, where the correlation between atrial and ventricular activity is disrupted.
Step-by-step explanation:
The QRS complex represents ventricular depolarization in the heart's electrical cycle; an elongated QRS interval can suggest an issue with the electrical signals reaching the ventricles, often indicative of some degree of atrioventricular (AV) block. In the context of ECG readings, whenever there is a disruption or delay in the conduction system, it can lead to various types of heart blocks.
Amongst these, the text provides key details on third-degree or complete AV block, where there is no correlation between the atrial and ventricular activities, distinguished by P waves and QRS complexes that appear unrelated to each other. Additionally, second-degree blocks, while not as severe as third-degree blocks, would consist of some P waves not followed by a QRS complex, which also signifies a disruption in atrioventricular conduction, although some signals still manage to pass through the AV node. While P waves are linked with atrial depolarization, the QRS complex is linked with ventricular depolarization, and disruptions in their normal intervals can hint at specific cardiac conditions.