What is 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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The sinoatrial (SA) node is innervated by the parasympathetic and the sympathetic nervous systems; the balance between these systems controls the pacemaker rate. Parasympathetic input via the vagus nerves decreases the SA nodal pacemaker and is the dominant input at rest, wheras sympathetic nerve input, as well as the adrenal medullary release of catecholamines, increases the sinus rate during exercise and stress.

Sinus node dysfunction (SND) is often secondary to senescence of the SA node and surrounding atrial myocardium. Medications may also contribute to, and can often unmask, subclinical SA dysfunction.

The epidemiology of SND is difficult to study, but patients with symptomatic SND are generally older (in the seventh or eighth decade of life) with frequent comorbid diseases.SND occurs as a result of disorders in automaticity, conduction, or both. SN fibrosis is the most common cause of SND.

The natural history of SND typically involves intermittent but progressive cardiac rhythm disorders, which have been associated with higher rates of other cardiovascular events and higher mortality. There is a tendency for the rhythm disturbances associated with SND to evolve over time, along with a higher likelihood of thromboembolic events and other cardiovascular events.

The treatment of sinus bradycardia and pauses starts with investigating/identifying any reversible causes, of which the most common are medications. Permanent pacemakers are often implanted in symptomatic patients with SND.

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