Prevalence of family history in patients with reflex syncope

Reflex syncope is defined by a rapid transient loss of consciousness caused by global cerebral hypoperfusion resulting from vasodilatation and/or bradycardia attributable to inappropriate cardiovascular reflexes. A hereditary component has been suggested, but prevalence of family history may differ among subtypes of reflex syncope, as these have different autonomic responses and pathogeneses may be diverse. The present study aimed to assess the prevalence of a positive family history of syncope and cardiovascular characteristics in patients with cardioinhibitory and vasodepressor reflex syncope. Patients (n=74) were classified into subtypes of reflex syncope - cardioinhibition/asystole (Vasovagal Syncope International Study subtypes II-B [VASIS II-B], n=38) or vasodepressor (VASIS III, n=36) - using the head-up tilt test. Family history was obtained by questionnaires supplemented by interview. Patients with cardioinhibitory syncope had a mean onset of disease 8 years earlier than vasodepressor patients (mean ± standard deviation 14.5 years ± 12.6 for cardioinhibitory patients compared to 22.4 years ± 11.9 for vasodepressor patients, p<0.001). Thirty-seven (50%) of 74 probands had a positive family history with at least one relative affected with syncope, arrhythmias, known sudden unexpected death, and/or heart disease. The prevalence of a positive family history was higher in patients with cardioinhibitory syncope compared to vasodepressor syncope (24 (63%) compared to 13 (36%); p=0.02). Overall, 40 first-degree relatives (26%) and 27 second- or third-degree relatives (25%) were affected. The most frequent events in families of patients with cardioinhibitory or vasodepressor reflex syncope were severe syncope and/or arrhythmias, known sudden unexpected deaths, and heart disease. In conclusion, prevalence of familial occurrence of syncope is in agreement with previous studies. However, a high occurrence of all-cardiovascular disorders in cardioinhibitory patients may reflect shared genetic susceptibility to these diseases.