Neurohormones in the Pathophysiology of Vasovagal Syncope in Adults

Abstract

Vasovagal syncope (VVS) is the most common cause of syncope across all age groups. Nonetheless, despite its clinical importance and considerable research effort over many years, the pathophysiology of VVS remains incompletely understood. In this regard, numerous studies have been undertaken in an attempt to improve insight into the evolution of VVS episodes and many of these studies have examined neurohormonal changes that occur during the progression of VVS events primarily using the head-up tilt table testing model. In this regard, the most consistent finding is a marked increase in epinephrine (Epi) spillover into the circulation beginning at an early stage as VVS evolves. Reported alterations of circulating norepinephrine (NE), on the other hand, have been more variable. Plasma concentrations of other vasoactive agents have been reported to exhibit more variable changes during a VVS event, and for the most part change somewhat later, but in some instances the changes are quite marked. The neurohormones that have drawn the most attention include arginine vasopressin [AVP], adrenomedullin, to a lesser extent brain and atrial natriuretic peptides (BNP, ANP), opioids, endothelin-1 (ET-1) and serotonin. However, whether some or all of these diverse agents contribute directly to VVS pathophysiology or are principally a compensatory response to an evolving hemodynamic crisis is as yet uncertain. The goal of this communication is to summarize key reported neurohumoral findings in VVS, and endeavor to ascertain how they may contribute to observed hemodynamic alterations during VVS.

Keywords: catecholamines; neuroendocrine; neurohormone; tilt-table testing; vasovagal syncope.

Figure 1

Data adapted from Ermis et al. (16) showing change of circulating Epi and NE concentrations (ordinate: pg/ml) measured at various anatomic sites during the course of HUT-induced syncope (Blue) or HUT without syncope (Green). See text for details.

Figure 2

Data derived from Kohno et al. (19) showing that the time to syncope during HUT was shorter (Time in Minutes on ordinate) as the Epi concentration increased (abscissa, pg/ml).