Sick sinus syndrome

Sick sinus syndrome (SSS), is a group of abnormal heart rhythms (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's primary pacemaker.[1] Tachycardia-bradycardia syndrome is a variant of sick sinus syndrome in which the arrhythmia alternates between slow and fast heart rates. Tachycardia-bradycardia syndrome is often associated with ischemic heart disease and heart valve disease.

Sick sinus syndrome
Other namesSinus dysfunction, or Sinoatrial node disease
Electrocardiogram from a man with bradycardia-tachycardia syndrome following mitral valvuloplasty, resection of the left atrial appendage and maze procedure. The ECG shows AV-junctional rhythm resulting in bradycardia at around 46 beats per minute. The second beat is most likely an atrial extrasystole, given the atypical P wave (negative in I, positive in aVR).
SpecialtyCardiology 
This ECG from the same patient shows atrial fibrillation at around 126 beats per minute.

Signs and symptoms

Even though many types of sick sinus syndrome produce no symptoms, a person may present with one or more of the following signs and symptoms:

  • Stokes-Adams attacks – fainting due to asystole or ventricular fibrillation
  • Dizziness or light-headedness
  • Palpitations
  • Chest pain or angina
  • Shortness of breath
  • Fatigue
  • Headache
  • Nausea

Complications

It can result in many abnormal heart rhythms (arrhythmias), including sinus arrest, sinus node exit block, sinus bradycardia, and other types of bradycardia (slow heart rate).[2]

Sick sinus syndrome may also be associated with tachycardias (fast heart rate) such as atrial tachycardia (PAT) and atrial fibrillation. Tachycardias that occur with sick sinus syndrome are characterized by a long pause after the tachycardia. Sick sinus syndrome is also associated with azygos continuation of interrupted inferior vena cava.

Causes

Disorders that cause scarring, degeneration, or damage to the sinoatrial node can cause sick sinus syndrome, including sarcoidosis, amyloidosis, hemochromatosis, Chagas' disease,[3] and cardiomyopathies.[2] Abnormal heart rhythms are often caused or worsened by medications such as digoxin, calcium channel blockers, beta-blockers, sympatholytic medications, and anti-arrhythmics.

Coronary artery disease, high blood pressure, and aortic and mitral valve diseases may be associated with sick sinus syndrome, although this association may only be incidental. The mechanism is related to delayed escape. Congenital SSS can be due to mutations of the gene responsible for formation of Alpha subunit of sodium channel (SCN5A).

Diagnosis

Ambulatory monitoring of the electrocardiogram (ECG) may be necessary because arrhythmias are transient.[4] The ECG may show any of the following:

Electrophysiologic tests are no longer used for diagnostic purposes because of their low specificity and sensitivity. Cardioinhibitory and vasodepressor forms of sick sinus syndrome may be revealed by tilt table testing.

Treatment

Artificial pacemakers have been used in the treatment of sick sinus syndrome.[5]

Bradyarrhythmias are well controlled with pacemakers, while tachyarrhythmias respond well to medical therapy.

However, because both bradyarrhythmias and tachyarrhythmias may be present, drugs to control tachyarrhythmia may exacerbate bradyarrhythmia. Therefore, a pacemaker is implanted before drug therapy is begun for the tachyarrhythmia.

Epidemiology

Sick sinus syndrome is a relatively uncommon syndrome in the young and middle-aged population. Sick sinus syndrome is more common in elderly adults, where the cause is often a non-specific, scar-like degeneration of the cardiac conduction system. Cardiac surgery, especially to the atria, is a common cause of sick sinus syndrome in children.

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References
  1. Dobrzynski H, Boyett MR, Anderson RH (April 2007). "New insights into pacemaker activity: promoting understanding of sick sinus syndrome". Circulation. 115 (14): 1921–32. doi:10.1161/CIRCULATIONAHA.106.616011. PMID 17420362.
  2. Semelka, M; Gera, J; Usman, S (May 2013). "Sick sinus syndrome: a review". American Family Physician (Review). 87 (10): 691–6. PMID 23939447.
  3. Keller KB, Lemberg L (March 2006). "The sick sinus syndrome". Am. J. Crit. Care. 15 (2): 226–9. PMID 16501143.
  4. Adán V, Crown LA (April 2003). "Diagnosis and treatment of sick sinus syndrome". Am Fam Physician. 67 (8): 1725–32. PMID 12725451.
  5. Drago F, Silvetti MS, Grutter G, De Santis A (July 2006). "Long term management of atrial arrhythmias in young patients with sick sinus syndrome undergoing early operation to correct congenital heart disease". Europace. 8 (7): 488–94. doi:10.1093/europace/eul069. PMID 16798761.
Classification
External resources
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