Waves, intervals and segments of the EKG
In essence the electrocardiogram is a drawing of the hearts electrical activity. The waves and segments of the EKG are therefore best understood in connection with the electrical conduction system of the heart. Here is a short overview:
- The P wave represents the depolarisation of the atria.
- The PQ interval represents the AV conduction (however including atrial conduction) and is measured from the beginning of the P wave to the beginning of the QRS complex.
- The QRS complex represents the depolarization of the ventricles beginning with the septum (the Q wave correspond to septum depolarization) and ending with the ventricular walls.
- The ST segment starts from the end of the QRS complex and ends at the beginning of the T wave. The ventricles are fully depolarized.
- The T wave represents ventricular repolarization. The QT interval (the T wave included) represents the duration of the ventricular systole.
- The U wave represents late ventricular repolarization (may not be visible).
The normal values of the PQ interval, the QRS complex and the corrected QT interval (QTc) are: