What is the pathophysiology of sinus node dysfunction (SND)?

Updated: Nov 30, 2018
  • Author: Bharat K Kantharia, MD, FRCP, FAHA, FACC, FESC, FHRS; Chief Editor: Mikhael F El-Chami, MD  more...
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Answer

The sinus node (SN) is a subepicardial structure normally located in the right atrial wall near the superior vena cava entrance on the upper end of the sulcus terminalis. It is formed by a cluster of cells capable of spontaneous depolarization. Normally, these pacemaker cells depolarize at faster rates than any other latent cardiac pacemaker cell inside the heart. Therefore, a healthy SN directs the rate at which the heart beats. Electrical impulses generated in the SN must then be conducted outside the SN in order to depolarize the rest of the heart.

SN activity is regulated by the autonomic nervous system. For example, parasympathetic stimulation causes sinus bradycardia, sinus pauses, or sinoatrial exit block. These actions decrease SN automaticity, thereby decreasing the heart rate.

Sympathetic stimulation, however, increases the slope of phase 4 spontaneous depolarizations. This increases the automaticity of the SN, thereby increasing the heart rate. Blood supply to the SN is provided by the right coronary artery in most cases.


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