Sick sinus syndrome

Sick sinus syndrome is a type of heart rhythm disorder. It affects the heart's natural pacemaker (sinus node), which controls the heartbeat. Sick sinus syndrome causes slow heartbeats, pauses (long periods between heartbeats) or irregular heartbeats (arrhythmias).

Sick sinus syndrome is relatively uncommon. The risk of developing it increases with age. Many people with sick sinus syndrome eventually need an implanted device called a pacemaker to keep the heart in a regular rhythm.

Sick sinus syndrome may also be called sinus node dysfunction or sinus node disease.

Most people with sick sinus syndrome have few or no symptoms. Symptoms may be mild or come and go — making them difficult to recognize at first.

Signs and symptoms of sick sinus syndrome may include:

• A sensation of rapid, fluttering heartbeats (palpitations)
• Chest pain or discomfort
• Confusion
• Dizziness or lightheadedness
• Fainting or near fainting
• Fatigue
• Shortness of breath
• Slower pulse (bradycardia)

Talk to your health care provider if you have any signs or symptoms of sick sinus syndrome. Many medical conditions can cause these problems. It's important to get a timely and accurate diagnosis.

If you have new or unexplained chest pain or think you're having a heart attack, call for emergency medical help immediately.

To understand the cause of sick sinus syndrome, it may be helpful to know how the heart typically beats.

The heart is made up of four chambers — two upper (atria) and two lower (ventricles). The rhythm of the heart is typically controlled by the sinus node, an area of specialized cells in the right upper heart chamber (right atrium).

This natural pacemaker produces electrical signals that trigger each heartbeat. From the sinus node, electrical signals travel across the atria to the ventricles, causing them to contract and pump blood to the lungs and body.

Typically, the sinus node creates a steady pace of electrical impulses. The pace changes depending on activity, emotions and other factors.

In sick sinus syndrome, the electrical signals are irregularly paced. The heartbeat can be too fast, too slow, interrupted by long pauses — or an alternating combination of these rhythm issues. Sick sinus syndrome is relatively uncommon, but the risk of developing it increases with age.

Causes of sick sinus node syndrome can include:

• Age-related wear and tear of heart tissues
• Damage to the sinus node or scarring from heart surgery
• Heart disease
• Inflammatory diseases affecting the heart
• Medications to treat high blood pressure, including calcium channel blockers and beta blockers
• Medications to treat irregular heartbeats (arrhythmias)
• Some Alzheimer's disease medications
• Neuromuscular diseases, such as muscular dystrophy
• Obstructive sleep apnea
• Rare genetic changes

Features of sick sinus syndrome include:

• Sinus bradycardia. The sinus node produces a slow heartbeat.
• Sinus arrest. Signals from the sinus node pause, causing skipped beats.
• Sinoatrial exit block. Signals to the upper heart chambers are slowed or blocked, causing pauses or skipped beats.
• Chronotropic incompetence. The heart rate is within regular range at rest but doesn't increase as much as it should with physical activity.
• Tachycardia-bradycardia syndrome. The heart rate alternates between unusually slow and fast rhythms, often with a long pause between heartbeats.

Sick sinus syndrome can occur at any age. It's most common in people in their 70s or older. Common heart disease risk factors might increase the risk of sick sinus syndrome. Risk factors for heart disease include:

• High blood pressure
• High cholesterol
• Excess body weight
• Lack of exercise

Complications of sick sinus syndrome include:

• Atrial fibrillation, a type of irregular heartbeat (arrhythmia)
• Heart failure
• Stroke
• Cardiac arrest