Sick sinus syndrome (SSS) is a group of three heart rhythm problems in which the heart’s natural pacemaker doesn’t work correctly. The sinus node is the pacemaker of the heart. It’s located in the right atrium and regulates the steady rhythmic beating of the heart. Normally, the sinus node produces a steady pace of regular electrical impulses. In sick sinus syndrome, these signals are abnormally paced. The sinus node is exquisitely sensitive and can increase or decrease the heart rate depending on levels of stress, caffeine, and exercise.
The heart rhythms of an individual with sick sinus syndrome can be too fast, too slow, interrupted by long pauses or a fluctuating combination of these rhythm issues. Sick sinus syndrome is uncommon, but the risk of developing it increases with age as the normal conduction system becomes increasingly fibrous with wear and tear of the sinus node. It occurs in men and women equally.
Frequently, individuals with sick sinus syndrome will require a pacemaker to keep their heart in a regular rhythm.
Sick sinus syndrome may be symptomatic and reveals a disruption in the normal function of the sinus node. Any of the following conditions can indicate sick sinus syndrome:
- Fast heart rate or tachycardia even at rest.
- Slow heart rate or bradycardia despite the body’s demands.
- Fluctuating abnormally slow and fast heart rates (tachycardia-bradycardia syndrome).
- Sinus breaks or stops when impulse formation ceases for at least 2-3 second intervals.
Sick sinus syndrome can also be intensified or appear in patients on other cardiac medications that affect the sinus node’s normal rhythmic firing. It affects roughly 3 in 10,000 people. Some patients could have fast heart rates or tachycardias that require medications to slow down the heart rate. When using these cardiac medications, the normal sinus node function may become suppressed so that the patient becomes symptomatic. Also, patients who have suffered a heart attack may have sustained damage to the sinus node and then develop sick sinus syndrome. Other conditions that can produce sick sinus syndrome include:
- thyroid disease,
- obstructive sleep apnea,
- muscular dystrophy,
- congenital heart disease,
- infiltrative heart diseases such as amyloid or sarcoid
The symptoms of sick sinus syndrome are usually a direct result of the fast vs. slow heart rates. These include:
- dizziness or lightheadedness
- syncope (loss of consciousness)
- fatigue and weakness
- angina (chest pain)
Any symptoms of syncope or chest pain require urgent medical assessment to exclude other more serious causes.
Risk Factors for Sick Sinus Syndrome
Although the exact cause of sick sinus syndrome is unknown, some factors are often associated with the condition, such as:
- Certain medications that treat High Blood Pressure and other heart diseases.
- Prior heart attack.
- Hyperkalemia – excessive potassium in the blood.
- Thyroid disease.
- Sleep apnea.
- Heart surgery.
In rare cases, sick sinus syndrome may be linked with conditions such as:
- Diphtheria (an infection that can damage the heart muscle)
- Muscular dystrophy – an inherited disease in which the body’s muscles are damaged and weak.
- Hemochromatosis – too much iron in the blood.
- Amyloidosis – a condition wherein a protein called amyloid is deposited in tissues or organs.
The diagnosis of sick sinus syndrome is usually given based on electrocardiogram (EKG) tracings during an episode. The EKG can be performed in a physician’s office or by outpatient monitoring with an ambulatory Holter or Event monitor.
Many patients with sick sinus syndrome do not exhibit symptoms during a physical examination by their physician.
Evidence of sick sinus syndrome may include:
- Irregular heart rhythm or pauses.
- A slower than normal pulse rate.
- Escape rhythms from other intra-cardiac pacemaker sites noted on a 12-lead EKG.
- A heart rhythm that interchanges between fast and slow rates, and low blood pressure.
There isn’t any clear medical treatment for symptomatic sick sinus syndrome. For patients that require medication to slow down a fast heart rhythm, a slow heart rate is an inescapable outcome. No reliable outpatient medication is currently available to heal the sinus node. With these limitations, patients with symptomatic sick sinus syndrome are referred for a pacemaker. Briefly, this procedure involves the creation of a pocket under the skin of the upper chest where the small electronic pacemaker device is implanted.
Electrical signals from the permanent pacemaker are delivered to the heart by one or two implantable intra-cardiac leads inserted in the veins of the chest underneath the collarbone. The pacemaker monitors the heart rhythm and rate 24 – 7. When a patient’s heart beats at a rate slower than the programmed lower limit, it will deliver an electrical impulse and pace the heart, consequently eliminating symptomatic episodes of bradycardia (slow heart rate).