Final answer:
The PR segment is part of the ECG that lies between the end of the P wave and the start of the QRS complex, while the PR interval includes the P wave and the PR segment, indicating the time between atrial depolarization and the onset of ventricular depolarization.
Step-by-step explanation:
The PR segment on an electrocardiogram (ECG) is a specific region that begins at the end of the P wave and ends at the beginning of the QRS complex. This segment represents the conduction delay between the end of atrial depolarization and the start of ventricular depolarization. On the other hand, the PR interval encompasses a slightly larger portion, starting at the beginning of the P wave and ending at the beginning of the QRS complex, thereby including the PR segment plus the P wave. The PR interval is significant in clinical settings because it reflects the time taken for an electrical impulse to travel from the sinoatrial (SA) node to the atrioventricular (AV) node. A delay in this conduction pathway can be detected by an elongation of the PR interval. An understanding of the PR segment and PR interval is crucial for interpreting ECGs and diagnosing cardiac conditions.