Sinus rhythm refers to the origination of the electrical activity coming from the sinus node — also known as the sinoatrial node, or SA node. This results in an upright P wave in lead II on the ECG.

Sinus rhythm (a.k.a. normal sinus rhythm) refers to the normal heart beat originating from the sinoatrial node. This is manifested as an upright P wave in lead II of the ECG. Sinus bradycardia ...