Reflex syncope due to exaggerated cardioinhibitory vagal response to photic stimulation: a case report

Transient loss of consciousness is a common presentation to emergency departments, medical assessment units, and cardiology and neurology outpatients. It is a presentation frequently resulting in hospital admission, or multiple presentations to health services and in up to a third of cases a specific aetiology is not identified. [D'Ascenzo F, Biondi-Zoccai G, Reed MJ, Gabayan GZ, Suzuki M, Costantino G, et al. Incidence, etiology and predictors of adverse outcomes in 43,315 patients presenting to the Emergency Department with syncope: an international meta-analysis. Int J Cardiol 2013;167:57-62.].

A 68-year-old female presented with an unexplained episode of collapse with amnesia. Initial cardiac and neurological investigations were normal. A sleep deprived electroencephalogram (EEG) with intermittent photic stimulation triggered a profound bradycardic response with a 12 second period of asystole interspersed with a single junctional beat. The EEG demonstrated slow delta and theta activity frequency waves without epileptiform spikes or sharp waves during the period of bradycardia consistent with decreased cerebral perfusion. A dual chamber pacemaker was implanted and the patient has remained asymptomatic since implantation.

This case highlights an unusually pronounced cardioinhibitory response to photic stimulation successfully treated with pacemaker implantation. 'Trigeminocardiac' reflex mechanisms are described which may explain this phenomenon in association with sinus node dysfunction.