Sick sinus syndrome (SSS), also known as sinus node dysfunction, is a relatively rare type of arrhythmia (abnormal heart rhythm). It is a condition in which the sinus node, which is located in the right atrium and serves as the heart’s natural pacemaker, is unable to set the pace of the heart as well as it should. Sick sinus is a syndrome, or a cluster of signs and symptoms that occur together, whether or not the cause of the condition is known. Advanced SSS is often marked by alternating rapid and slow heart rhythms, neither of which produces a good cardiac output. Patients can often feel this yo–yo effect, which results in not enough blood circulating through the body. If left untreated, sick sinus syndrome can lead to heart–related complications such as heart failure. In addition, patients with SSS are at increased risk for heart attack, even after treatment. However, treatment for the disease dramatically lowers risk of complications.
Symptoms of sick sinus syndrome (SSS) may develop over a lengthy span of time, even over a period of years, or there may be none present. Because they may not seem important on their own, people may not seek treatment until SSS has reached an advanced stage. Symptoms include:
- Syncope (fainting) spells.
- Bradycardia (a heart rate that is consistently less than 60 beats per minute).
- Palpitations (a feeling in the chest of a fast or pounding heartbeat).
- Angina (chest pain) caused by a lack of blood flow in the heart.
- Heart failure (new or worsening).
- Dizziness or lightheadedness.
- Shortness of breath.
- Muscle aches.
- Fatigue or unusual tiredness.
- Disturbed sleep.
There are many factors that may cause or contribute to the development of sick sinus syndrome (SSS). They include:
- Cardiac ischemia. A lack of oxygen in heart muscles and tissue due to a restriction of blood flow to the heart, usually caused by coronary artery disease.
- Heart attack. Scarring or death of heart muscle due to lack of oxygen. Oxygen-rich blood is blocked by a blood clot in a coronary artery, usually due to plaque-related narrowing of the artery (coronary artery disease).
- Hyperkalemia. Too much potassium circulating in the blood. Potassium enters the body through food and is removed from the body as urine produced by the kidneys. Hyperkalemia is usually the result of kidney failure.
- Antiarrhythmics. Medications used to treat arrhythmias (abnormal heart rhythms) have been connected to SSS. These medications may be withheld or reduced in the event of SSS. However, if a pacemaker is implanted to regulate the heart rhythm, antiarrhythmics may be prescribed to help prevent abnormally fast heart beats (tachycardia).
- Beta blockers. Medications that reduce the workload of the heart and lower blood pressure. They are commonly prescribed for conditions such as angina (a certain type of chest pain, pressure or discomfort) or heart failure. They are also prescribed for people who have high blood pressure (hypertension).
- Hypothyroidism. Abnormally low levels of thyroid hormones in the blood.
- Sleep apnea. A sleep disorder in which a person’s breathing stops and starts many times during sleep.
- Electrolyte disorders. Electrolytes are biochemical compounds that play an important role in controlling fluid levels, maintaining the body’s acid/base balance, nerve conduction, blood clotting and muscle contraction (including that of the heart). They include calcium, potassium, chloride and sodium.
- Cardiomyopathy. A disease of the heart in which the muscles' ability to pump blood is inhibited or weakened, usually due to the enlargement, thickening and/or stiffening of the heart muscle.
- Heart surgery. Operations on the heart, particularly the atria, are a common cause of SSS in children. The syndrome can be caused by thickened scarlike tissue forming on the atria, blocking the natural electrical patterns of the heart. In adults, there is a risk of developing SSS following catheter ablation (elimination) of part or all of the sinus node to treat tachycardia.
How it is Diagnosed:
Diagnosis of sick sinus syndrome (SSS) is usually made after a medical history and physical examination by a cardiologist. The syndrome is difficult to diagnose because patients often have few symptoms, and many patients are elderly and have other cardiac conditions. In general, a physician looks for the following combinations of signs, in addition to arrhythmias, to make a diagnosis of SSS.
- A heart rate that is consistently slower than normal (60 beats per minute), which may or may not be accompanied by episodes of a rapid heart rate (more than 140 beats per minute).
- Normal or low blood pressure.
- Symptoms that appear only during episodes of arrhythmia.
- An electrocardiogram (EKG) result that shows one or more of the various arrhythmias associated with sick sinus syndrome.
Because of the nature of the disease, sick sinus syndrome (SSS) often is not diagnosed until its advanced stages. If the syndrome is detected even though it is producing no symptoms, no treatment is necessary. However, if the patient is taking medications that may worsen the condition, those medications likely will be stopped and/or replaced with safer alternatives. Treatment is necessary once SSS enters the advanced stages. The most common treatment is a combination of an artificial pacemaker and antiarrhythmic medications.