Sick sinus syndrome (SSS) is a relatively uncommon heart rhythm disorder. SSS is not a specific disease, but rather a group of signs or symptoms that indicate the sinus node, the heart’s natural pacemaker, is not functioning properly. A person with SSS may have heart rhythm that are too slow (bradycardia), too fast (tachycardia), or one that alternates between the fast and slow (bradycardia-tachycardia).

What is Sick Sinus Syndrome?

The sinus node is a specialized group of cells in the upper chamber of the heart, the atria, that creates electrical signals that regulate the pace and rhythm of the heartbeat. Normally, the sinus node produces a regular, steady pattern of signals. With SSS, the pattern is irregular. Sick sinus syndrome may be due to defects in the heart itself, or it can be related to factors outside the heart.

Symptoms of Sick Sinus Syndrome

Most people with sick sinus syndrome have few or no symptoms. In others, symptoms may come and go. These symptoms can include:

• Slower than normal pulse (bradycardia) 
• Fainting (syncope)
• Feeling tired all the time (fatigue)
• Weakness
• Shortness of breath (dyspnea)
• Chest pain (angina)
• Disturbed sleep
• Confusion
• Heart palpitations (feeling like your heart is racing, pounding, or fluttering)

Risk Factors for Sick Sinus Syndrome

While the exact cause of SSS is unknown, some factors, however, often are associated with the condition, such as:

• Age
• Previous heart attack (myocardial infarction)
• Medications to treat high blood pressure and other heart diseases
• Hyperkalemia (too much potassium in the blood)
• Thyroid disease
• Sleep apnea
• Heart surgery

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

• Diphtheria (an infection that can damage the heart muscle)
• Hemochromatosis (excess iron in the blood)
• Muscular dystrophy (an inherited condition in which the body’s muscles are damaged and weak)
• Amyloidosis (a condition in which a protein called amyloid is deposited in tissues or organs)