Abnormalities of sympathetic and parasympathetic autonomic function in subjects with defaecation syncope

Defaecation syncope is defined as blacking out at, or around, the time of defaecation. It is associated with increased mortality; however, patients rarely voluntarily report symptoms. We have examined autonomic function in a cohort of patients with defaecation syncope.

We prospectively identified all subjects referred to our unit with symptoms of defaecation syncope or presyncope on direct questioning. All subjects had autonomic function tests using beat to beat blood pressure measurement synchronized with R-R interval allowing real time assessment of autonomic function.

Seven patients were identified who presented with defaecation syncope. Compared with age and sex matched controls, subjects had abnormalities of both sympathetic and parasympathetic autonomic function consistent with mild-moderate autonomic failure. On specific intervention syncope stopped in all subjects: 3 had culprit medication withdrawn, 3 received medication to increase blood pressure and 1 in whom cardioinhibition was demonstrated improved with permanent pacemaker insertion. Two subjects who had colonoscopy had profound haemodynamic changes during the procedure associated with syncope.

Symptoms of syncope on defaecation are associated with autonomic failure. With appropriate therapeutic intervention our subjects all improved.