Sick sinus syndrome — also known as sinus node disease or sinus node dysfunction — is a group of heart rhythm problems (arrhythmias) in which the heart's natural pacemaker (sinus node) doesn't work properly.
The sinus node is an area of specialized cells in the upper right chamber of the heart that controls the rhythm of your heart. Normally, the sinus node produces a steady pace of regular electrical impulses. In sick sinus syndrome, these signals are abnormally paced.
The heart rhythms of a person with sick sinus syndrome can be too fast, too slow, punctuated by long pauses — or an alternating combination of these rhythm problems. The syndrome is relatively uncommon, but the risk of developing it increases with age.
Many people with sick sinus syndrome eventually need a pacemaker to keep the heart in a regular rhythm.
Most people with sick sinus syndrome initially have few or no symptoms. In some cases, symptoms come and go.
When they occur, sick sinus syndrome signs and symptoms might include:
- Slower than normal pulse (bradycardia)
- Dizziness or lightheadedness
- Fainting or near fainting
- Shortness of breath
- Chest pains
- A sensation of rapid, fluttering heartbeats (palpitations)
When to see a doctor
If you have lightheadedness, dizziness, fainting, fatigue, shortness of breath or palpitations, talk to your doctor. Many medical conditions can cause these signs and symptoms — including sick sinus syndrome — and it's important to identify the problem.
Your heart is made up of four chambers — two upper (atria) and two lower (ventricles). The rhythm of your heart is normally controlled by the sinus node, an area of specialized cells in the right atrium.
This natural pacemaker produces the electrical impulses that trigger each heartbeat. From the sinus node, electrical impulses travel across the atria to the ventricles, causing them to contract and pump blood to your lungs and body.
If you have sick sinus syndrome, your sinus node isn't functioning properly, causing your heart rate to be too slow (bradycardia), too fast (tachycardia) or irregular.
Types of sick sinus syndrome and their causes include:
- Sinoatrial block. Electrical signals move too slowly through the sinus node, causing an abnormally slow heart rate.
- Sinus arrest. The sinus node activity pauses, causing skipped beats.
- Bradycardia-tachycardia syndrome. The heart rate alternates between abnormally fast and slow rhythms, usually with a long pause (asystole) between heartbeats.
What makes the sinus node misfire?
Diseases and conditions that cause scarring or damage to your heart's electrical system can be the reason. Scar tissue from a previous heart surgery also can be the cause, particularly in children. Rarely, the cause can be genetic.
Sick sinus syndrome can be unmasked by medications, such as calcium channel blockers or beta blockers used to treat high blood pressure, or by other conditions causing the heartbeat to be slower or faster than normal. In most cases, the sinus node doesn't work properly because of age-related wear and tear to the heart muscle.
Sick sinus syndrome can occur at all ages, even infancy. Because it usually develops over many years, it's most common in people over age 65.
In rare cases, sick sinus syndrome can be associated with certain conditions such as muscular dystrophy and other diseases that may affect the heart.
When your heart's natural pacemaker isn't working properly, your heart can't perform as efficiently as it should. This can lead to:
- Atrial fibrillation, a chaotic rhythm of the upper chambers of the heart
- Heart failure
- Cardiac arrest