Sick sinus syndrome

Key words and synonyms: Bradycardia-tachycardia syndrome, tachycardia-bradycardia syndrome, tachy-brady syndrome, sinus node dysfunction, SND, SSS. Sinus arrest, sinus bradycardia, are forms or variants of sick sinus syndrome.

Overview
Sick sinus syndrome, also called Sinus node dysfunction, is a group of abnormal heart rhythms (arrhythmias) caused by a malfunction of the sinus node, the heart's "natural" pacemaker.

Subclassification of variants of sinus node dysfunction

 * 1) Bradycardia-tachycardia syndrome is a variant of sick sinus syndrome where atrial tachyarrhythmias such as atrial flutter and fibrillation alternate with prolonged periods of asystole.
 * 2) Chronotropic incompetence
 * 3) Sinus bradycardia
 * 4) Sinus arrest
 * 5) Sinus node exit block
 * 6) Sinus pause

Common Causes
Sick sinus syndrome 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.

Symptoms
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
 * Palpitations
 * Chest pain or angina
 * Shortness of breath
 * Fatigue
 * Headache

Diagnosis
Ambulatory monitoring of the electrocardiogram (ECG) may be necessary because arrhythmias are transient. The ECG may show any of the following
 * 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

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
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.

==ACC / AHA Guidelines- Recommendations for Permanent Pacing in Sinus Node Dysfunction (DO NOT EDIT) == {{cquote|

Class I
1. Permanent pacemaker implantation is indicated for SND with documented symptomatic bradycardia, including frequent sinus pauses that produce symptoms. (Level of Evidence: C)

2. Permanent pacemaker implantation is indicated for symptomatic chronotropic incompetence. (Level of Evidence: C)

3. Permanent pacemaker implantation is indicated for symptomatic sinus bradycardia that results from required drug therapy for medical conditions. (Level of Evidence: C)

Class IIa
1. Permanent pacemaker implantation is reasonable for SND with heart rate less than 40 bpm when a clear association between significant symptoms consistent with bradycardia and the actual presence of bradycardia has not been documented. (Level of Evidence: C)

2. Permanent pacemaker implantation is reasonable for syncope of unexplained origin when clinically significant abnormalities of sinus node function are discovered or provoked in electrophysiological studies. (Level of Evidence: C)

Class IIb
1. Permanent pacemaker implantation may be considered in minimally symptomatic patients with chronic heart rate less than 40 bpm while awake. (Level of Evidence: C)

Class III
1. Permanent pacemaker implantation is not indicated for SND in asymptomatic patients. (Level of Evidence: C)

2. Permanent pacemaker implantation is not indicated for SND in patients for whom the symptoms suggestive of bradycardia have been clearly documented to occur in the absence of bradycardia. (Level of Evidence: C)

3. Permanent pacemaker implantation is not indicated for SND with symptomatic bradycardia due to nonessential drug therapy. (Level of Evidence: C)}}