Epidemiology

Epidemiology of neurally mediated syncope

The prevalence of syncope in the general population is extremely common. Almost everybody seems to have either experienced or witnessed an episode. Syncopal events often do not reach medical attention, particularly in the young in whom most episodes are considered to be innocent neurally mediated events (Soteriades et al., 2002;Wieling et al., 2004b).

Studies in young populations show a strikingly high incidence of syncope. Two recent surveys of the frequency of syncope in medical students demonstrated that 20-25% of males and 40-50% of females report to have experienced at least one such episode (Ganzeboom et al., 2003;Serletis et al., 2006). The majority of the syncope triggers identified in these students involved stresses or conditions that affect orthostatic blood pressure control. Neurally mediated syncope was therefore a likely cause of the symptoms in these young subjects. The incidence peak of presumed neurally mediated syncope around the age of 15 years and the much higher incidence in young females is a consistent finding (fig. 1)(Ganzeboom et al., 2003;Colman et al., 2004a;Ganzeboom et al., 2006;Serletis et al., 2006;Sheldon et al., 2006). A family history of presumed neurally mediated syncope in the first degree relatives is often present in young fainting subjects (Mathias et al., 1998;Serletis et al., 2006).

Compared to the 30% incidence of presumed neurally mediated syncope in young medical students, the prevalence of epileptic seizures in a similar young age group is much lower (less than 1%) (Wallace et al., 1998) and syncope resulting from cardiac arrhythmias or structural heart disease, i.e. cardiac syncope, is even less common (Colman et al., 2004a).

Influence of age

A first neurally mediated syncopal episode is rare in adults aged 35-60 years. About 80% of the syncope patients in this age group have experienced presumed neurally mediated episodes as teenagers and adolescents, which may of help in establishing a diagnosis (Ganzeboom et al., 2006, Serletis et al 2006).

Patients with presumed neurally mediated syncope present themselves to general practitioners according to a bimodal age distribution (fig. 2) with a first peak at the age of 15 years, and a second peak in ollder adults and elderly (Colman et al., 2004a). ~Figure 2~ Typical vasovagal syncope is less common in these older subjects. It is not unusual that the episodes of vasovagal syncope an older patient experiences are far les typical than vasovagal syncope at younger age. Thus, neurally mediated syncope may be considered as a chronic life long condition, with different clinical presentation and triggers among episodes (Kurbaan et al., 2003;Colman et al., 2004a;Sheldon et al., 2006).

In older subjects cardiac causes of syncope, orthostatic and postprandial hypotension and carotid sinus hypersensitivity are more frequent (Kapoor, 1994;Youde et al., 2000;Mukai & Lipsitz, 2002). This can be attributed to diminished efficiency of cardiovascular regulatory systems, to medication affecting orthostatic blood pressure control and to increased prevalence of organic disease (e.g. structural heart disease, cardiac arrhythmia’s (Brady & Shen, 1999). In the elderly, multiple causes of syncope are often present and the medical history may be less reliable than in the young, for example syncope may be erroneously reported as a fall (McIntosh et al., 1993;Kapoor, 1994;Benke et al., 1997;Kenny, 2003)