Sinus node dysfunction
Sinus node dysfunction (sick sinus syndrome) is failure of the sinoatrial node to generate or transmit impulses appropriately, causing sinus bradycardia, pauses, arrest, or the brady-tachy syndrome. Diagnosis rests on correlating symptoms with ECG or ambulatory monitoring, and symptomatic irreversible disease is treated with a permanent pacemaker.
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What this article covers
- Overview
Definition: sinus node dysfunction (sick sinus syndrome) is inappropriate impulse formation or exit from the sinoatrial node, producing inappropriate bradycardia, sinus pauses or arrest, chronotropic…
- Epidemiology
Primarily a disease of older adults from age-related nodal fibrosis.
- Risk factors
Age-related degeneration and fibrosis of the sinoatrial node.
- Pathophysiology
Impaired automaticity: degeneration of sinoatrial pacemaker cells slows or halts intrinsic firing.
- Clinical features
Fatigue and exertional intolerance from chronotropic incompetence.
- Differential diagnosis
Physiologic sinus bradycardia: a slow rate that is asymptomatic and rises normally with exercise, unlike the chronotropic incompetence of SND (sinus bradycardia).
- Diagnosis
Establish by correlating symptoms with documented sinus bradycardia, pauses, arrest, or chronotropic incompetence: the diagnostic basis is ECG or ambulatory monitoring showing inappropriate sinus…
- Management
First-line, treat only symptomatic disease and remove reversible causes: stop or reduce offending nodal drugs (beta-blockers, calcium channel blockers, digoxin) and correct hypothyroidism before committing to device therapy.
- Complications
Syncope and falls with injury. Thromboembolism and stroke from associated atrial fibrillation.
- Prognosis
Good with pacing, which relieves symptoms though it does not prolong life on its own.
- Prevention
Avoid unnecessary nodal-blocking drugs in older patients.
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Related articles
- Bradycardia
Bradycardia is a heart rate below 60 per minute, ranging from a benign physiologic finding to symptomatic sinus node dysfunction or high-grade atrioventricular block. Management is driven by symptoms and stability: unstable patients receive atropine and then transcutaneous pacing or a chronotropic infusion, and durable symptomatic conduction disease is treated with a permanent pacemaker.
- Atrial fibrillation
Atrial fibrillation is a supraventricular tachyarrhythmia with disorganized atrial activation and an irregularly irregular ventricular response, the most common sustained arrhythmia and a major cause of stroke. Diagnosis is by ECG showing no discrete P waves with irregular RR intervals, and management addresses rate or rhythm control, stroke prevention by CHA2DS2-VASc-guided anticoagulation, and the underlying cause.
- Syncope
Syncope is a transient loss of consciousness from global cerebral hypoperfusion with spontaneous complete recovery. The central task is separating benign reflex and orthostatic causes from dangerous cardiac syncope, using history, examination, and ECG, since cardiac syncope carries a risk of sudden death; treatment is directed by mechanism, from reassurance and hydration for reflex syncope to a pacemaker, ICD, or structural intervention for cardiac syncope.
- Sinus bradycardia
Sinus bradycardia is a sinus rhythm below 60 per minute with normal P-wave morphology and a normal PR interval. It is most often a benign physiologic finding in fit or sleeping people, and treatment is needed only when it is symptomatic or reflects a reversible cause such as drugs, ischemia, or hypothyroidism.