Formed by stimulation of the SA node, the P wave is a small upward deflection that accompanies depolarization of the atrial fibers. The wave is followed by the actual contraction of the atria by a fraction of a second. During the expression of the P wave, the ventricles of the heart are in diastole. A dysfunction of the SA node is perhaps suggested by a abnormal or missing P wave.
This is the period of time from the beginning of the P wave to the start of the QRS wave on the recording.It is showed by this interval that the amount of time needed for the SA depolarization to reach the ventricles. A conduction problem is suggested by a prolonged P-R interval from the AV node.
Beginning as a short downward deflection, the QRS wave continues as a sharp upward spike, and ends as a downward deflection. The depolarization of the ventricles is indicated by the QRS wave. The ventricles are in systole and blood is being ejected from the heart during this interval. The atria repolarize during this interval as well, however, this event is hidden by the greater depolarization happening in the ventricles. Heart problems of the ventricles are normally showed by an abnormal QRS wave.
The time duration known as the S-T interval indicates the period between the completion of ventricular depolarization and initiation of repolarization. When the heart receives insufficient oxygen, the S-T interval is depressed.
Ventricular repolarization forms the T wave. Altered T waves will be formed by an arteriosclerotic heart, as will various other heart diseases.