The Sinus Rhythms

The driving impulse of the heart ordinarily arises in the P cells of the sinoatrial node. Pace-making foci are not, however, limited to the sinus node; others exist outside of it in the atrial myocardium. This observation has lead some electrocardiographers to speak of the atrial pace-making complex, a term that includes foci both within and outside of the sinus node.