Current Concepts in Sick Sinus Syndrome

Sinus node dysfunction, or sick sinus syndrome (SSS), is defined as a disorder of impulse formation within the sinus node and impulse conduction out of the node. The disorder of impulse formation not only involves the sinus node but also affects subsidiary pacemakers.¹⁻³Thus, the term SSS reflects a more diffuse disease of the specialized conduction system involving the atria, the atrioventricular node, and occasionally the common His bundle and the bundle branches. This disorder is not of a single cause but has a constellation of causes (Table 1). Electrocardiographic manifestations may predate the development of symptoms by several years. Once symptomatic sick sinus node dysfunction develops, recovery is unlikely and medical or surgical intervention is required. We will discuss the electrophysiology of normal and abnormal sinus node function. With early clinical recognition and appropriate therapy, morbidity and death from SSS can be prevented. ANATOMY AND PHYSIOLOGY OF THE