Sick sinus syndrome
|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).|
Sick sinus syndrome (SSS), also called sinus dysfunction, or sinoatrial node disease ("SND"), is a group of abnormal heart rhythms (arrhythmias) presumably caused by a malfunction of the sinus node, the heart's primary pacemaker. 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.
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
- Chest pain or angina
- Shortness of breath
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.
Disorders that cause scarring, degeneration, or damage to the sinoatrial node can cause sick sinus syndrome, including sarcoidosis, amyloidosis, hemochromatosis, Chagas' disease, and cardiomyopathies. 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).
- Inappropriate sinus bradycardia
- Sinus arrest
- Sinoatrial block
- Tachy-Brady Syndrome
- 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.
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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