Sinus Rhythm

Sinus rhythm occurs when the sinus node, the normal cardiac pacemaker, depolarises spontaneously, and the consequent wave of depolarisation follows the natural pathways through the heart.

The autonomic nervous system normally slows the spontaneous discharge rate of the sinus node from 100 bpm to about 70 bpm in adults. The limits of the rate of the rhythm are 50 bpm and 120 bpm.

The following ECG trace shows sinus rhythm at a rate of 77 bpm. Each QRS complex (shaded) is preceded by a P wave (arrowed) of regular shape and offset.

Electrocardiogram: Sinus Rhythm
Electrocardiogram: Sinus Rhythm