Waveforms, intervals, segment

P wave

atrial depolarization, contraction of the atria

QRS wave

represents ventricular depolarization, contraction of the ventricles (atrial repolarization is not visible but occurs phase)

T wave

represents ventricular repolarization, relaxation of the ventricules

U wave

Not always visible but represents a repolarization of the bundle of His and Purkinje fibers

PR interval

starts at the beginning of the P wave and ends at the beginning of the Q wave. Represents the time from the beginning of atrial depolarization to the beginning of ventricular depolarization

QT intervals

starts at the beginning of the Q wave and ends at the end of the T wave. Represents the time from the beginning of ventricular depolarization to the end of ventricular repolarization

ST segment

starts at the end of the S wave and ends at the beginning of the T wave. Represents the time from the end of ventricular depolarization to the beginning of ventricular repolarization