The Sick Sinus Syndrome

"THE SICK sinus syndrome" is a term coined by Ferrer1referring to a constellation of signs, symptoms, and ECG criteria defining sinus node dysfunction in a clinical setting. These criteria, which have been described by many investigators,2-7include sinus bradycardia, sinus arrest, sinoatrial block, alternating bradyarrhythmias and tachyarrhythmias, and carotid hypersensitivity. Any one or combination of these features may be seen in the typical sick sinus patient who has syncope or other evidence of cerebral dysfunction. Symptoms, nevertheless, are a manifestation of failure of escape pacemaker function and not truly a feature of sinus node malfunction. SINUS NODE AS PACEMAKER The sinus node is a highly organized cluster of specialized cells located in the area of the junction between the superior vena cava and the right atrium. Microscopically, three cell types have been described in the sinus node: P cells, transitional cells, and working cells.8The P