Sick sinus syndrome overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sahar Memar Montazerin, M.D.[2]
Overview
Sick sinus syndrome (SSS) is a term used to describe a number of different abnormal heart rhythms (arrhythmias) caused by a malfunction of the sinus node, the heart's "natural" pacemaker. It encompasses disorders causing reduced automaticity of the sinoatrial node, exit block, and sinus arrest. The syndrome primarily affects the elderly, and is associated with paroxysmal atrial fibrillation or flutter in approximately half of the patients and with distal conduction disease in up to one tenth of patients.
Historical Perspective
Sick sinus syndrome was first described by Dr. Keith and Dr. Flack, in 1907. In 2015, MYH6 gene mutations were first implicated in the pathogenesis of sick sinus syndrome. In 1972, Dr. Mandel found a new method of assessing sinus node function, known as sinus node recovery time.
Classification
Pathophysiology
Sick sinus syndrome occurs as an improperly propagated signal from the sinoatrial (SA) node. Age-dependent progressive fibrosis of the sinus nodal tissue and Remodeling of a sinuatrial node are the potential mechanisms of this abnormally formed signal propagation. MYH6 gene may also be involved in the pathogenesis of this condition.
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 caused by a variety of conditions including but not limited to myocardial infarction, atrial fibrillation, drugs or toxins, infections,medications, electrolyte abnormalities, hypothermia, hypoxemia, hypercarbia, and acidosis.
Epidemiology and Demographics
The incidence of SSS increases with increasing age, occurring in 1 of every 600 cardiac patients above the age of 65 years old. Sick sinus syndrome (SSS) usually occurs in individuals older than 50 years old. There is no difference in incidence of SSS between men and women. In addition, the black population was found to have a 41% lower risk of developing SSS as compared to the white population.
Natural history, Complications and Prognosis
Sick sinus syndrome natural history progress over decades. Patients are usually asymptomatic at first, but then symptoms may present due to the insufficient blood supply. Sinus pause or severe bradycardia may present with the central nervous system (CNS) under perfusion which manifests with presyncope or syncope. Possible complications of sick sinus syndrome include cerebrovascular events, stroke, transient ischemic events, renal, gastrointestinal hypo-perfusion, thromboembolism, Fatigue and exercise intolerance. The syndrome is progressive, which means it usually gets worse over time.
History and Symptoms
Patients with sick sinus syndrome (SSS) may present with nonspecific symptoms or be asymptomatic. 50 percent of patients present with syncope or pre-syncope related to the decreased cerebral perfusion secondary to bradyarrhythmias or tachyarrhythmias. Some of the symptoms that may develop among patients include memory loss, dizziness or light-headedness, Palpitations, chest pain or angina, shortness of breath, fatigue, and headache.
Physical Examination
Patients with sick sinus syndrome usually appear normal. Physical examination of patients with sick sinus syndrome is usually remarkable for bradycardia, tachycardia, and signs of the organ hypoperfusion.
Laboratory Findings
There is no laboratory findings associated with the diagnosis of sick sinus syndrome. However, electrolyte abnormalities may be one of the causes. Possible metabolic disturbances associated with sick sinus syndrome include hyperkalemia, hypokalemia, hypoglycemia, hypocalcemia, and hypoxia.
Electrocardiogram
Sick sinus syndrome is a collection of heart rhythm disorders that include sinus bradycardia, sinus pauses and sinus arrest. Sick sinus syndrome can evolve towards causing atrial fibrillation, atrial flutter, ectopic atrial tachycardia, sinus node reentrant tachycardia, and tachycardia-bradycardia.
Echocardiography
There are no echocardiography/ultrasound findings associated with sick sinus syndrome.
X Ray
There are no x-ray findings associated with sick sinus syndrome.
CT Scan
There are no CT scan findings associated with sick sinus syndrome.
MRI
There are no MRI findings associated with sick sinus syndrome.
Other Imaging Findings
There are no other imaging findings associated with sick sinus syndrome.