Sick Sinus Syndrome Associated Conditions

There is no specific, known cause of sick sinus syndrome. Some factors, however, often are associated with the condition, such as: Age-related damage to the heart muscle. Wear-and-tear on the heart over time may weaken the SA node or damage the heart muscle that conducts the electrical signal. As we grow older, we also have fewer "pacing" cells in the heart.

• Heart attack (myocardial infarction). An infarct is an area of dead heart muscle caused by a lack of oxygen. This damage can affect the SA node, or give rise to abnormal electrical signals in other parts of the heart.
• Medications prescribed for conditions such as high blood pressure and other heart diseases may contribute to sick sinus syndrome. Patients with SA node problems who have a too-fast heart rate, for example, may develop symptoms of SSS when they take medications that slow this fast heartbeat.
• Hyperkalemia means there is too much potassium circulating in the blood. Normally, potassium is removed by urine produced in the kidneys. Hyperkalemia usually is a sign of kidney disease. It is on etype of "electrolyte disorder" and can cause abnormal heart rhythms.
• Other electrolyte disorders. Electrolytes are biochemical compounds that play a role in controlling fluid and chemical balances in the body, and in nerve conduction, and muscle contraction (including the heart muscle). Electrolytes include calcium, potassium, chloride and sodium.
• Thyroid disease. A low level of thyroid hormone in the blood (hypothyroidism) is associated with a too-slow heart rate.
• Sleep apnea, a condition in which a person's breathing stops and starts repeatedly during the night.
• Heart surgery. A common cause of SSS in children is heart surgery, especially in the upper chambers, or atria. Scarred tissue that forms in the atria can block the normal pattern of electrical signals from the SA node.

In rare cases, SSS may be associated with conditions such as:

• Diphtheria. The toxin produced by this infection can cause severe damage to the heart muscle. Diphtheria is uncommon in the U.S. because most American children are vaccinated against the disease, but it is common in some other parts of the world.
• Hemochromatosis (a disease in which the body absorbs too much iron).
• Muscular dystrophy (an inherited condition in which the muscles of the body are damaged and weak and do not function normally).
• Amyloidosis (a condition in which a body protein called amyloid is deposited in tissues or organs, including the heart).