Sick sinus syndrome
|Sick sinus syndrome|
|Classification and external resources|
Sick sinus syndrome (SSS), also called sinus node dysfunction (SND), is an umbrella term for a group of abnormal heart rhythms (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's primary pacemaker. Bradycardia-tachycardia syndrome is a variant of sick sinus syndrome in which slow arrhythmias and fast arrhythmias alternate. It is often associated with ischaemic heart disease and valvular lesions.
Sick sinus syndrome is a relatively uncommon syndrome. 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).
Sick sinus syndrome may also be associated with tachycardias (fast heart rate) such as paroxysmal supraventricular tachycardia (PSVT) and atrial fibrillation. Tachycardias that occur with sick sinus syndrome are characterized by a long pause after the tachycardia.
Abnormal rhythms are often caused or worsened by medications such as digitalis, calcium channel blockers, beta-blockers, sympatholytic medications, and anti-arrhythmics. Disorders that cause scarring, degeneration, or damage to the conduction system can cause sick sinus syndrome, including sarcoidosis, amyloidosis, Chagas' disease, and cardiomyopathies.
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.
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 is due to mutations of gene responsible for formation of Alpha subunit of sodium channel.
A Russian study showed that the heterozygous variant of connexin 40 polymorphism gene variant is more frequent among patients with sick sinus node syndrome and their healthy relatives than in persons of control group, suggesting a link between the gene and the disease.
Even though many types of sick sinus syndrome produce no symptoms, patients may present with:
- Stokes-Adams attacks – fainting due to asystole or ventricular fibrillation
- Dizziness or light-headedness
- Chest pain or angina
- Shortness of breath
- Inappropriate sinus bradycardia
- Sinus arrest
- Sinoatrial block
- Atrial fibrillation with slow ventricular response
- A prolonged asystolic period after a period of tachycardias
- Atrial flutter
- Ectopic atrial tachycardia
- Sinus node reentrant tachycardia
- Wolff-Parkinson-White syndrome
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.
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.
- 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.
- Keller KB, Lemberg L (March 2006). "The sick sinus syndrome". Am. J. Crit. Care 15 (2): 226–9. PMID 16501143.
- Chernova, AA (2011). "[Polymorphism of Connexin 40 Gene a Novel Genetic Marker of the Sick Sinus Node Syndrome.]". Kardiologiia 51 (5): 17–9. PMID 21649591.
- Adán V, Crown LA (April 2003). "Diagnosis and treatment of sick sinus syndrome". Am Fam Physician 67 (8): 1725–32. PMID 12725451.
- 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.