Final answer:
The PQ interval on an ECG indicates the duration it takes for the electrical impulse to travel from the sinoatrial node, through the atria, and delay at the atrioventricular node, up to the beginning of the ventricles' depolarization, which is represented by the start of the QRS complex.
Step-by-step explanation:
In an ECG pattern, the PQ interval indicates how long it takes for the cardiac impulse to travel from the sinoatrial node through the atria and then through the delay at the atrioventricular node before passing on to the ventricles. This interval reflects the time period for the onset of atrial depolarization (beginning of the P wave) to the beginning of ventricular depolarization (start of the QRS complex). Should there be any delay in the passage of the impulse, it would become apparent in an elongation of the PQ interval.
The PQ interval is clinically significant because it can reveal potential issues with the electrical conduction system of the heart. For example, if the PQ interval is prolonged, it could indicate a first-degree heart block, signifying a delay in the conduction of electrical impulses from the atria to the ventricles. Conversely, a PQ interval that is too short may suggest that the electrical impulse is bypassing the normal conduction pathways.