Sick Sinus Syndrome

The sinoatrial node (also called the sinus node) is called the heart's natural pacemaker. When its ability to function normally is disturbed and no cause can be identified, the condition is known as sick sinus syndrome.

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



While some people with certain types of sick sinus syndrome have no symptoms, others with sick sinus syndrome may have:

  • A low heart rate
  • Fatigue
  • Heart palpitations
  • Lethargy


Causes and Risk Factors

No cause for sick sinus syndrome has been identified. It may be a defect in the sinoatrial node. However, many patients have features that suggest there may be abnormalities of the atrioventricular nodal, as well.



A doctor will note the medical and family history and symptoms before conducting a physical examination.

A slow pulse, especially if it is irregular, may be a sign of sick sinus syndrome. In this case, the doctor 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.

Another test the doctor may order is tilt-table testing. This is usually recommended for people who have a history of fainting for an unknown reason and don't have any structural heart disease. During this test, blood pressure and heart rate are continuously monitored while the person lays on a mechanized table that is tilted at a 60-degree to 80-degree angle for 15 to 20 minutes at each angle. If the person’s blood pressure doesn't increase, a drug is given intravenously to raise the heart rate by approximately 20 beats a minute, at which point the test is repeated.



If sick sinus syndrome is causing symptoms, an artificial pacemaker may need to be implanted to regulate heart rhythms.

Drugs to prevent arrhythmias (irregular heart rhythms) may also be prescribed.

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