Sick sinus syndrome is an umbrella term that covers three heart rhythm problems (arrhythmias):
sinus bradycardia, which causes a slow heart rate
tachycardias, which cause fast heart rates, often followed by a very slow heart rate. Types of tachycardias include atrial fibrillation, atrial flutter/tachycardia, and supraventricular tachycardia
bradycardia-tachycardia, which causes alternating slow and fast heart rhythms
A problem with a part of the heart called the sinus node causes these arrhythmias. This group of specialized cells in the upper right chamber of the heart controls the heart's rhythm by sending electrical signals that tell the heart to beat. In someone with sick sinus syndrome, these signals do not come at a steady pace.
Sick sinus syndrome is a relatively uncommon problem. How many people have it is hard to say because it often doesn't cause any symptoms and therefore many people may be living with it and not know it. One study estimates that sick sinus syndrome occurs in about one in every 600 people with cardiovascular disease older than 65. It is even less common in younger people. The average age of a person with sick sinus syndrome is about 68. Of the three arrhythmias that fall under the term sick sinus syndrome, sinus bradycardia is the most common.
What causes sick sinus syndrome is not completely understood, but we do know that disorders that cause scarring, degeneration, or damage to the heart can cause sick sinus syndrome. These include:
idiopathic degenerative disease (changes to the area of the heart around the sinus node that occur with aging)
high blood pressure
structural defects in the heart
Certain medications can make abnormal heart rhythms worse. These include the following drugs, which are all prescribed for various heart problems:
digitalis (also known as digoxin)
calcium channel blockers