Sick sinus syndrome (SSS), also called sinus node dysfunction, is a group of heart rhythm disorders caused by abnormal function of the sinoatrial (SA) node, the heart’s natural pacemaker. The SA node normally generates regular electrical impulses that set the heart rate; in sick sinus syndrome, this function is impaired, resulting in a heart rate that is too slow, too fast, or alternates between the two.
Common manifestations include: sinus bradycardia (an inappropriately slow heart rate at rest or during exertion); sinus pauses or arrest (the SA node fails to fire for a period, causing a pause in the heart rhythm that may cause dizziness or syncope); and tachycardia-bradycardia syndrome, in which episodes of abnormally fast heart rate (often atrial fibrillation or flutter) alternate with episodes of very slow rate, sometimes occurring at the termination of the fast rhythm as the depressed SA node struggles to restart.
Symptoms depend on severity and may include dizziness, light-headedness, palpitations, breathlessness, fatigue, and syncope. The condition most commonly affects older adults and is associated with ageing of the SA node and surrounding atrial tissue, though it can also be caused by coronary artery disease, infiltrative heart disease, or medication effects.
Diagnosis is confirmed by correlating symptoms with documented rhythm abnormalities, using a 12-lead ECG, Holter monitoring, or implantable loop recorder. Treatment is usually permanent pacemaker implantation, which reliably prevents symptomatic bradycardia and pauses. The tachycardia component may additionally require rate-control medication or rhythm-control therapy.
« Back to Glossary Index