Final answer:
A Long PR interval indicates a delayed impulse in the AV node, visible on an ECG as an extended period from atrial depolarization to the initiation of the ventricular response.
Step-by-step explanation:
A Long PR interval, greater than 0.20 seconds, typically indicates a delayed impulse in the AV node. This is clinically relevant, as it represents a delay in the passage of the impulse from the sinoatrial (SA) node to the AV node. In a first-degree or partial AV block, this delay can be recognized on an electrocardiogram (ECG) as an abnormally long PR interval. The PR interval is the period from the beginning of atrial depolarization (the P wave) to the initiation of the QRS complex. A delay in this interval suggests that the impulse is taking longer than normal to pass through the AV node before it reaches the ventricles.