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A prolonged PR interval on an ECG reflects a delay in the conduction of electrical impulses through the atrioventricular (AV) node. This can indicate the presence of heart block, which occurs when the electrical signals from the atria to the ventricles are slowed or completely interrupted. Heart block can vary in severity, including first-degree, second-degree, and third-degree heart block, all of which manifest as a prolonged PR interval.

In first-degree heart block, there is a consistent prolongation of the PR interval, while in second-degree heart block (types I and II), this is characterized by intermittent dropped beats. Third-degree heart block results in a complete dissociation between atrial and ventricular activity, although the PR interval can vary significantly. Thus, recognizing a prolonged PR interval is crucial in identifying and managing conditions related to heart block effectively.

In contrast, the other conditions listed do not typically associate with a prolonged PR interval. Atrial flutter may show a rapid atrial rate with distinct flutter waves rather than a delay in PR conduction. Sinus tachycardia shows a normal PR interval but with an increased heart rate. Wolff-Parkinson-White syndrome is characterized by pre-excitation and typically presents with a shortened PR interval, rather