Sick Sinus Syndrome

The heart muscle is responsible for circulating blood throughout the body. The heart is aided by a group of specialized cells known as the sinoatrial node (also called the sinus node) located in the upper right chamber of the heart. The sinus node is the heart's natural pacemaker, controlling the heart's rhythm. When its ability to function normally is disturbed and no cause can be identified, the condition is known as sick sinus syndrome.

Abnormal heart rhythms associated with sick sinus syndrome can be too fast, too slow, punctuated by long pauses, or an alternating combination of all of these rhythm problems.

One variation of sick sinus syndrome is a pattern of slow heartbeats, followed by a period of very rapid heartbeats. This can cause atrial fibrillation or flutter.


The main symptom of sick sinus syndrome is an abnormal heart rhythm. Initially, this symptom may go unnoticed by patients because there are no other symptoms present. When symptoms are present they may include:

  • Low heart rate (bradycardia)
  • Fast heart rate (tachycardia)
  • Fainting
  • Dizziness
  • Lightheadedness
  • Fatigue
  • Weakness
  • Shortness of breath
  • Chest pain
  • Confusion
  • Quickly tiring during physical activity

Causes and Risk Factors

Sick sinus syndrome occurs when the sinus node is not working properly. This can be caused by:

  • 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 slow and fast rhythms, usually with a long pause (asystole) between heartbeats

Sick sinus syndrome can occur at any age. However, the condition often develops slowly over time and is therefore more common in patients 70 years of age or older.

In some cases, sick sinus syndrome can be associated with muscular dystrophy and other diseases that may affect the heart.

Other risk factors include:


Diagnosis of sick sinus syndrome will generally begin with the physician taking a medical history and performing a physical exam. A slow pulse, especially if it is irregular, may be a sign of sick sinus syndrome. In this case, the physician may order a Holter monitor test to record the heart's electrical activity over a 24-hour period as the person goes about regular activities.

During the physical exam, the physician may perform a tilt table study to evaluate the heart and blood pressure when the body changes positions. Based on the tilt table test and the patient’s symptoms, an accurate diagnosis can often be made.

Other diagnostic tests may include an electrocardiogram (EKG), a painless procedure that provides a picture of the electrical activity of the heart and how the heart is working.

Electrophysiology studies may also be used to look at the electrical system of the heart.


Treatment of sick sinus syndrome will vary from one patient to the next and will depend on the type, severity and cause of their condition. In some cases, when the abnormal heart rhythm is caused by an underlying condition, treatment may focus on addressing that underlying condition. Other treatment options may include adjusting current medications and sometimes surgery.

Because medications such as beta blockers or calcium channel blockers — which are used to control blood pressure and other conditions — may cause sick sinus syndrome, a patient’s current medication routine may be adjusted. If the patient's condition increases their risk of stroke, blood thinning medications may be added to their medication routine.

In some cases, if other treatment options do not adequately address the condition, surgery may be needed to implant a pacemaker.

The knowledgeable and highly trained staff at the Cedars-Sinai Heart Institute will work with each patient to determine the best treatment option.