Sick sinus syndrome — also known as sinus node disease or sinus node dysfunction — is the name for a group of heart rhythm problems (arrhythmias) in which the sinus node — the heart's natural pacemaker — 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.
A person with sick sinus syndrome may have heart rhythms that are too fast, too slow, punctuated by long pauses — or an alternating combination of all of these rhythm problems. Sick sinus syndrome is relatively uncommon, but the risk of developing sick sinus syndrome 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 may come and go.
When they do occur, sick sinus syndrome symptoms may 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)
Many of these signs and symptoms are caused by reduced blood flow to the brain when the heart beats too fast or too slowly.
When to see a doctor
If you have spells of 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 chambers (atria) and two lower chambers (ventricles). The rhythm of your heart is normally controlled by the sinoatrial (SA) node — or sinus node — an area of specialized cells located 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 out to your lungs and body.
If you have sick sinus syndrome, your sinus node isn't functioning properly, so your heart rate may be too slow (bradycardia) or 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.
- 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 may be the cause, particularly in children.
Sick sinus syndrome may also be set off by medications, such as calcium channel blockers or beta blockers used to treat high blood pressure, heart disease or other conditions. However, in many cases, the sinus node doesn't work properly because of age-related wear and tear to the heart muscle.
Sick sinus syndrome can occur in people of all ages, even infants. Because it usually develops slowly, over many years, it's most common in people around age 70.
In rare cases, sick sinus syndrome may also 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 a very slow heart rate, which may cause fainting.
In rare cases, long periods of slow heart rate or fast heart rate can keep your heart from pumping enough blood to meet your body's needs — a condition called heart failure.
If you have a type of sick sinus syndrome called bradycardia-tachycardia syndrome, you also may be at a higher risk of developing a blood clot in your heart that may lead to a stroke. That's because the fast heart rhythm that occurs in bradycardia-tachycardia syndrome is often atrial fibrillation.
Atrial fibrillation is a chaotic rhythm of the upper chambers of the heart that can cause blood pooling in the heart. Blood clots are more likely to form when blood flow through the heart is altered in any way. A blood clot can break loose and travel to the brain, causing a stroke.