SE-3 Electrocardiograph Service Manual Operating Principle
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Figure 3-1 Composition of ECG
P wave: the sequential activation (depolarization) of the right and left atria
QRS complex: the right and left ventricular depolarization (normally the ventricles are
activated simultaneously)
ST-T wave: the ventricular repolarization
U wave: the origin of this wave is not clear - but probably represents "after-depolarization" in
the ventricles.
PR interval: the interval from the onset of the atrial depolarization (P wave) to the onset of the
ventricular depolarization (QRS complex)
QRS duration: the duration of the ventricular muscle depolarization
QT interval: the duration of the ventricular depolarization and repolarization
RR interval: the duration of the ventricular cardiac cycle (an indicator of the ventricular rate)
PP interval: the duration of the atrial cycle (an indicator of the atrial rate)
3.3 Lead
The 12-lead ECG provides spatial information about the heart's electrical activity in three
approximately orthogonal directions.
Right
Left
Superior
Inferior
Anterior
Posterior
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