Differential Diagnosis of Vasovagal Syncope: Sick Sinus Syndrome

Abstract

Sick sinus syndrome (SSS) can be diagnosed only when there is a clear correlation between symptoms and sinus node (SN) dysfunction. In the absence of such correlation, the mechanism of undocumented intermittent symptoms such as syncopal spells in patients with permanent mild sinus bradycardia remains uncertain. Some clinical data suggest that a reflex mechanism is likely to be involved in many patients with syncope and sinus bradycardia: (1) the course of syncope is very variable from patient to patient; (2) syncope does not recur in more than half of unpaced patients with SSS; (3) syncope recurs in up to 20 % of SSS patients during long-term follow-up, despite adequate pacing; (4) the prognosis does not appear to be different between SSS patients with and without neurologic symptoms. The results of some clinical studies, where head-up tilt testing and carotid sinus massage with the method of symptoms were performed in patients with syncope and sinus bradycardia, seem to confirm a reflex mechanism as the cause of syncope in most cases. However, a depressed SN automaticity, expressed by much prolonged SN recovery time, suggests a role of SN dysfunction in the origin of syncope. Patients with syncope and permanent mild sinus bradycardia, without much prolonged SN recovery time, should be managed as the patients with syncope and normal sinus rate.