Hemodynamic significance of heart rate in neurally mediated syncope

Vasovagal syncope: An overview of pathophysiological mechanisms

Syncope is a short-term transient loss of consciousness, characterized by rapid onset and complete spontaneous recovery. According to the 2018 European Society of Cardiology guidelines, three different types of syncope have been identified. However, all forms of syncope share a common final pathophysiological event, global cerebral hypoperfusion, which results from the inability of the circulatory system to maintain blood pressure at the level required to efficiently supply blood to the brain. The vasovagal syncope (VVS) is the most common form of syncope. Although, VVS is generally harmless, its frequent occurrence can negatively affect quality of life and increase the risk of adverse events. The pathophysiological mechanisms underlying VVS remain obscure. The multifaceted nature of VVS presents a veritable challenge to understanding this condition and developing preventative strategies. Thus, the aim of this review was to discuss the factors contributing to the pathogenesis of VVS and provide guidance for future research.

Advance in the understanding of vasovagal syncope in children and adolescents

BACKGROUND

Vasovagal syncope (VVS) accounts for 60-80% of cases of neurally mediated syncope. VVS results from acute orthostatic intolerance and recurrent syncopal attacks, which can seriously affect an individual's quality of life. In addition, some children even experience trauma during attacks. Therefore, it is particularly important to clarify the pathogenesis of VVS. The aim of our study is to reveal the latest research progress of VVS.

DATA SOURCES

Literature that involved the pathogenesis of VVS were selected from Cochrane Library (1990-2019), EMBASE (1991-2019) and PubMed (1968-2019) databases.

RESULTS

Hypovolemia, autonomic dysfunction, vasomotor dysfunction, baroreceptor reflex abnormalities, endothelial dysfunction, serotonin surges, and gut microbiota were involved in the underlying mechanism of VVS.

CONCLUSIONS

VVS is not always a benign prognosis. Various aspects were involved in its pathogenesis. Bezold-Jarish reflex, dysfunction of the autonomic nervous system, genetic factors and so on played important roles in VVS; however, the mechanism remains unclear.

Are women really more affected by vasovagal syncope than men?

It is commonly reported that vasovagal syncope (VVS) is more frequent in women. Presently, this issue has never been investigated. The purpose of this review was to evaluate, through an extensive review of the literature, whether women are really more affected by VVS than men. The gender distribution was investigated in individuals with classical and nonclassical VVS. The database PubMed was searched using the terms 'syncope', 'vasovagal syncope', 'neurally mediated syncope' and 'tilt testing'. Twelve studies dealing with classical and 75 with nonclassical VVS were eligible. In the individuals with classical (N = 1861) and nonclassical VVS (N = 9696), a trend towards a greater percentage of women emerged (P = 0.14 and 0.07, respectively). In the total population with VVS (N = 11 557), the percentage of women was significantly higher than that of men (58 versus 42%, P = 0.03). Most of the individuals were young or middle-aged. In 84% of the studies, the percentage of women was greater than that of men. A separate analysis was carried out in older VVS patients (≥60 years) and only two studies were eligible to be evaluated. Considering that almost all the studies were carried out in the western nations, where the number of men and women is almost superimposable until the age of 65 years and a bias by gender has never been reported in the management of VVS, these data strongly suggest that young and middle-aged women are more affected by VVS than their male counterparts. At present, data are too scant to draw a definitive conclusion in older VVS patients.

Head-up tilt test provokes dynamic alterations in total peripheral resistance and cardiac output in children with vasovagal syncope

AIM

This study examined the total peripheral vascular resistance (TPVR) and cardiac output changes due to the head-up tilt test (HUTT) in children with vasovagal syncope (VVS).

METHODS

From December 2013 to January 2016, we recruited 77 children diagnosed with VVS group at Peking University First Hospital, China, and 28 children without VVS provided the control group. Heart rate, blood pressure, TPVR, cardiac output and baroreflex sensitivity were monitored during the HUTT.

RESULTS

In the supine position, TPVR and baroreflex sensitivity were higher in the patients with VVS than the controls, but cardiac output did not differ between the two groups. There were obvious increases in the VVS patients from TPVR in the supine position to the prepositive response period (p < 0.05), then the positive response period (p < 0.01). However, we noted the opposite trend in cardiac output, from the supine position to the prepositive response period (p < 0.01) then the positive response period (p < 0.01).

CONCLUSION

During HUTT, children with VVS demonstrated increases in TPVR but decreases in cardiac output, during the transition from the supine position to the positive response. This response might be involved in the pathogenesis of VVS.