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Sick Sinus Syndrome



Introduction

Sick Sinus Syndrome 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, the sinus node beats abnormally causing slow heart rate (bradycardia), rapid heart rate (tachycardia) or alternating slow and fast rhythms.

Sick sinus syndrome is relatively uncommon. When it does occur, it usually affects people who are at least 60 years old. Some people with sick sinus syndrome need a pacemaker to keep the heart in a regular rhythm.

Signs and symptoms

Rhythm problems can occur if the signals through the sinus node are blocked (sinoatrial node block), the sinus node pauses or temporarily stops, or signals alternate fast and slow (called tachycardia-bradycardia syndrome):
  • Sinoatrial block. Electrical signals move too slowly through the sinus node, causing an abnormally slow heart rate.
  • Sinus arrest. The sinus node activity pauses.
    • Tachycardia-bradycardia syndrome. The heart rate alternates between abnormally fast and slow rhythms, often with a long pause (asystole) between heartbeats.
Most people with sick sinus syndrome have few or no symptoms. Signs and symptoms of sick sinus syndrome may come and go. They may include:
  • Fatigue.
  • Dizziness or lightheadedness.
  • Fainting or near-fainting.
  • Shortness of breath.
  • Chest pains.
  • Trouble sleeping.
  • Confusion or difficulty remembering things.
  • A sensation of rapid, fluttering heartbeats (palpitations).
Many of these symptoms are a result of reduced blood flow to the brain when the heart beats too fast or too slowly.

Causes

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 node (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.

A normal sinus node paces your resting heart between 60 and 100 beats a minute. If you have sick sinus syndrome, your sinus node isn't functioning properly, so your heart rate may be too slow or too fast.

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 most cases, the sinus node doesn't work properly because of age-related wear and tear to the heart muscle.

Treatment

Treatment for sick sinus syndrome focuses on eliminating or reducing unpleasant symptoms. If you aren't bothered by symptoms, you may only need regular checkups to monitor your condition. For people who are bothered by symptoms, the treatment of choice is usually an implanted electronic pacemaker.

Medication changes
Your doctor may start by looking at your current medications to see if any of them could be interfering with the function of your sinus node. Medications used to treat high blood pressure or heart disease — such as beta blockers or calcium channel blockers — can worsen abnormal heart rhythms. In some cases, adjusting these medications can relieve symptoms.

Pacing the heart
Most people with sick sinus syndrome need a permanent artificial pacemaker to maintain a regular heartbeat. This small, battery-powered electronic device is implanted under the skin near your collarbone during a minor surgical procedure. The pacemaker is programmed to stimulate or "pace" your heart as needed to keep it beating normally.

The type of pacemaker you need depends on the type of irregular heart rhythm you're experiencing. Some rhythms can be treated with a single-chamber pacemaker, which uses only one wire (lead) to pace one chamber of the heart — in this case, the atrium. However, most people with sick sinus syndrome benefit from dual-chamber pacemakers, in which one lead paces the atrium and one lead paces the ventricle.

Additional treatments for fast heart rate
If you have rapid heart rate as part of your sick sinus syndrome, you may need additional treatments to control these rhythms:
  • Medications. If you have a pacemaker and your heart rate is still too fast, you doctor may prescribe anti-arrhythmia medications to prevent fast rhythms. If you have atrial fibrillation or other abnormal heart rhythms that increase your risk of stroke, you may need a blood-thinning medicine, such as warfarin (Coumadin).
  • AV node ablation. This procedure can also control fast heart rhythms in people with pacemakers. It involves applying radiofrequency energy through a long, thin tube (catheter) to destroy (ablate) the tissue around the atrioventricular node between the atria and the ventricles. This stops fast heart rates from reaching the ventricles and causing problems.
  • Radiofrequency ablation of atrial fibrillation. This procedure is similar to AV node ablation. However, in this case, ablation targets the tissue in the atria that triggers atrial fibrillation. This actually eliminates atrial fibrillation itself, rather than just preventing it from reaching the ventricles.


Information obtained from National Institute of Health
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