What Causes Sick Sinus Syndrome?Sick sinus syndrome can occur when the sinus node is affected by a form of fibrosis associated with aging. This fibrosis in the sinus node can cause sinus bradycardia. That same age-related fibrosis also commonly affects the heart muscle of the atria, which can cause atrial fibrillation. Finally, the fibrosis can also affect the AV node, which produces a propensity for heart block.
What Symptoms Are Caused By Sick Sinus Syndrome?In people with sick sinus syndrome, the most prominent symptoms are usually those due to a slow heart rate -- becoming easily fatigued, lightheadedness, or syncope (loss of consciousness).
People with sinus node disease who also have episodes of atrial fibrillation will frequently experience both symptoms of bradycardia caused by their sinus node disease, and symptoms of tachycardia (especially palpitations), caused by episodes of atrial fibrillation. These patients are said to have bradycardia-tachycardia syndrome, or "brady-tachy syndrome."
The most troublesome symptom associated with brady-tachy syndrome is syncope. The syncope usually occurs immediately following an episode of atrial fibrillation, and is produced by a prolonged pause in the heart rate. The pause occurs because, when the sinus node is already "sick," an episode of atrial fibrillation tends to even further suppress its function. So when the atrial fibrillation suddenly stops, the sinus node may require several seconds to "wake up" and begin generating electrical impulses again. During this interval, there may be no heart beat at all for 10 or more seconds -- leading to extreme lightheadedness, or syncope.
How Is Sick Sinus Syndrome Diagnosed?Diagnosing sick sinus syndrome is typically not difficult. The correct diagnosis is usually pretty apparent when a person who complains of typical symptoms is found to have significant sinus bradycardia on their electrocardiogram (ECG). The "brady-tachy" variety of sick sinus syndrome is diagnosed when a patient with sinus node disease is also discovered to have episodes of atrial fibrillation.
Because the fibrosis that causes sinus node disease sometimes affects the AV node, patients with brady-tachy syndrome may also have a partial heart block, and therefore, a relatively slow heart rate when they are in atrial fibrillation. So whenever a patient in atrial fibrillation has a relatively slow heart rate (in the absence of medication aimed at slowing the heart rate), that slow rate should be a strong clue, for an alert doctor, that the patient may also have sick sinus syndrome.
How Is Sick Sinus Syndrome Treated?Virtually all people with sick sinus syndrome should be treated with a permanent pacemaker.
A pacemaker is especially important for people who have the brady-tachy form of sick sinus syndrome, for two reasons. First, these people have a relatively high risk of experiencing syncope (from those prolonged pauses when the atrial fibrillation terminates). And second, many of the drugs that are often used to treat atrial fibrillation -- beta blockers, calcium channel blockers, and antiarrhythmic drugs -- may make sinus node disease much worse. Implanting a pacemaker will prevent syncope, and will allow the doctor to treat atrial fibrillation much more safely.
Kaplan BM, Langendorf R, Lev M, Pick A. Tachycardia-bradycardia syndrome (so-called "sick sinus syndrome"). Pathology, mechanisms and treatment. Am J Cardiol 1973; 31:497.
Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. Circulation 2008; 117:e350.