Answer:
Conduction of impulse from the SA node through the AV node
Explanation:
An electrocardiogram (EKG or ECG) is a record of the patient's heart's electrical activity as show on a monitor or printed on paper as a waveform. Each complete waveform normally consists of a few distinct landmarks and characteristics, such as the P wave, Q wave, QRS complex, and P-R interval.
The P wave is the low-amplitude first bump above the baseline on an EKG, representing atrial depolarization, the period in which both atria (top chambers of the heart) receive electrical signaling from the sinoatrial node (SA node) to contract, sending blood rushing into both ventricles (bottom chambers of the heart) in preparation for contraction of their own.
The Q wave is the slight dip below the baseline, representing interventricular septal depolarization, during which the electrical signal descends from the SA node through the atrioventricular node (AV node) and into the bundle of His within the wall separating the two ventricles (septum) and essentially synchronizes the depolarization of the ventricles so they can produce a strong contraction during the subsequent, high-amplitude QRS complex.
The PR interval is measure from the beginning of the P wave to the beginning of the of the Q wave or the beginning of the QRS complex. It represents proper conduction of the electrical signaling from the SA node through the AV node as the heart prepares for that ventricular contraction.