Pathophysiology of Reflex Syncope: A Review

Wayne O. Adkisson MD; David G. Benditt MD


J Cardiovasc Electrophysiol. 2017;28(9):1088-1097. 

In This Article

Clarification of Nomenclature Related to Reflex Syncope

Over the years, the published literature surrounding reflex syncope has been replete with a wide range of terms. Inevitably, confusion has arisen due to the diverse terminology. The ESC Syncope guidelines[2] have provided some clarity, and we here provide our understanding of current best terminology usage.

Reflex syncope is the preferred term encompassing all conditions in which neural-reflexes modify heart rate (cardioinhibition) and/or vascular tone (vasodepression) so as to predispose to systemic hypotension of sufficient severity to cause a transient period of inadequate cerebral perfusion resulting in syncope or near-syncope. Thus, reflex syncope incorporates a broad range of conditions including: (1) vasovagal reactions, (2) CSS, and (3) the situational faints, as will be discussed.

Neurally mediated syncope or neurally mediated reflex syncope are terms that have been used in a manner synonymous with reflex syncope and were proposed to be umbrella terms for "reflex syncope." The word "reflex" implies a neural-mediated component; therefore, "neurally mediated" is redundant. The simpler term "Reflex syncope" is preferred. Finally, "neurally mediated syncope" or "neurally mediated reflex syncope" are umbrella terms and should not be used as a synonym for "vasovagal syncope," a specific type of reflex syncope.

Neurocardiogenic syncope was originally proposed as an umbrella term for reflex syncope. However, "neurocardiogenic" highlights the cardiac effects at the expense of the vascular ("vasodepressor") element that is a key aspect of these conditions. This term has also been inappropriately used as a synonym for the specific condition, "vasovagal syncope." The term "neurocardiogenic" is best abandoned.

Vasodepressor syncope is a term that describes a specific form of any of the reflex syncopes in which the vascular element substantially dominates, and the cardioinhibitory element is absent or very minor. A pure "vasodepressor" faint is a rare; use of the term "vasodepressor syncope" implies insight into the hypotensive mechanism that goes beyond the usual knowledge that physicians have in most cases of syncope. Again, "vasodepressor syncope" has also been used as a synonym for "vasovagal syncope" leading to unnecessary confusion. Given this circumstance, the term "vasodepressor syncope" should be abandoned.

"Neurogenic" syncope is yet another term used infrequently as a synonym for "Reflex syncope," but it has no compelling utility and may result in confusion with other conditions such as "neurogenic orthostatic hypotension." "Neurogenic," in the context of the reflex faints, should be discarded.

Vasovagal syncope is the preferred term used for that specific form of reflex syncope in which the faint occurs in the setting of emotional distress or in the absence of a specific identifiable trigger other than upright posture. It is usually classified separately from the situational faints as the "trigger" is often unclear. Further, the vasovagal faint is so frequent that it merits its own category.

"Common faint," "innocent faint," and "emotional faint" have each been used as synonyms for "vasovagal syncope." Of these, common faint is the most reasonable synonym for "vasovagal syncope" as it implies that this form of syncope is very frequent. While it is true that VVS is not associated with an increase in mortality, there is nevertheless increased risk of injury (especially in older patients), and VVS can also be very disruptive for some patients. Consequently, VVS is not at all "innocent" and that term should be abandoned. Furthermore, the term should not be used as synonym for "psychogenic pseudosyncope."

Situational faint is an appropriate umbrella term for those specific reflex faints in which the "trigger" is clear-cut (e.g., coughing, micturition, etc.). These syndromes will be discussed in more detail below.

Carotid sinus syndrome is a specific form of reflex syncope in which the trigger of the reflex is presumed to be baroreceptors in the neck. CSS may be considered as a "situational" faint, but is more often classified separately as a unique condition.

As a rule, the more specific term, assuming sufficient certainty exists, should be used for the condition diagnosed. One should no more refer to "micturition syncope" as "reflex syncope" than one should refer to "typical atrial flutter" as "supraventricular tachycardia"; while both are technically correct, the more specific term provides a great deal of more clarity.