Sick sinus syndrome

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 minutes. The second beat is most likely an atrial extrasystole, given the atypical P wave (negative in I, positive in aVR).

This ECG from the same patient shows atrial fibrillation at around 126 beats per minute.

Sick sinus syndrome, also called sinus node dysfunction, is a group of abnormal heart rhythms (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's primary pacemaker.^[1] Bradycardia-tachycardia syndrome is a variant of sick sinus syndrome in which slow arrhythmias and fast arrhythmias alternate.

Causes

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,^[2] 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.the congenital SSS is due to mutations of gene responsible for formation of Alpha subunit of sodium channel

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
• Nausea

Diagnosis

Ambulatory monitoring of the electrocardiogram (ECG) may be necessary because arrhythmias are transient.^[3] 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

Pacemakers have been used in the treatment of sick sinus syndrome.^[4]

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.

References