Neurally-mediated syncope

Abstract

"Neurally-mediated (reflex) syncope" refers to a reflex response that, when triggered, gives rise to vasodilation and/or bradycardia; however, the contribution of each of these two factors to systemic hypotension and cerebral hypoperfusion may differ considerably. The initial evaluation may lead to a certain diagnosis in the case of classical vasovagal syncope and of situational syncope. Classical vasovagal syncope is diagnosed if precipitating events such as fear, severe pain, emotional distress, instrumentation or prolonged standing, are associated with typical prodromal symptoms. Situational syncope is diagnosed if syncope occurs during or immediately after urination, defecation, cough or swallowing. In the absence of a certain diagnosis, absence of cardiac disease, long history of syncope, syncope after sudden unexpected unpleasant sight, sound or smell, prolonged standing at attention or crowded, warm places, nausea and vomiting, post-prandial and post-exercise state suggest a neurally-mediated cause which needs to be confirmed by specific tests. Among them, the most useful are carotid sinus massage and tilt testing. In general, education and reassurance are the sufficient initial treatment. Additional treatment may be necessary in high-risk or high-frequency settings. Treatment is not necessary in patients who have sustained a single syncope and are not having syncope in a high-risk setting. It is valuable to assess the relative contribution of cardioinhibition and vasodepression before embarking on treatment as there are different therapeutic strategies for the two aspects. Even if evidence of utility of such an assessment exists only for the carotid sinus massage, it is recommended to extend this assessment also by means of tilt testing or implantable loop recorder. Tilt training and isometric leg and arm counterpressure maneuvers are indicated in patients with recurrent vasovagal syncope. Cardiac pacing is indicated in patients with cardioinhibitory or mixed carotid sinus syndrome and in patients with cardioinhibitory vasovagal syncope with a frequency > 5 attacks per year or severe physical injury or accident and age > 40 years. The evidence fails to support the efficacy of any drug.