CARDIOVASCULAR MEDICINE

New insights into the mechanism of neurally mediated syncope

M A Mercader¹, P J Varghese¹, S J Potolicchio², G K Venkatraman², S W Lee¹

¹ Division of Cardiology, Department of Medicine, The George Washington University, Washington DC, USA
² Department of Neurology, The George Washington University

Correspondence to:
Correspondence to:
Dr P J Varghese, The George Washington University Medical Center, Department of Medicine, Division of Cardiology, 2150 Pennsylvania Avenue, NW, Suite 4–414, Washington DC 20037, USA;
domjxv{at}gwumc.edu

Objective: To determine the role of the cerebral cortex in neurally mediated syncope, the electroencephalograms (EEG) of patients recorded during head up tilt table test were analysed.

Design: Retrospective study.

Setting: University hospital.

Patients: 18 patients with syncope or near syncope underwent head up tilt table test with simultaneous ECG and EEG monitoring.

Methods: Standard 70° tilt table test was done with simultaneous ECG and EEG monitoring. EEG waveforms were analysed by both visual inspection and spectral analysis.

Results: 6 of 18 patients (33%) had a positive tilt table test. Before syncope slow waves increased in patients with a positive test. In addition, five of six tilt positive patients (83%) had slow wave activity that lateralised to the left side of the brain (mean (SD) 822 (724) v 172 (215) µV², p < 0.05), while none of the tilt negative patients exhibited lateralisation (24 (15) v 26 (19) µV², NS). Spectral analysis showed that the lateralisation occurred in the frequency. The lateralisation preceded the event by 5–56 seconds (18 (21) seconds).

Conclusions: EEG activity lateralises to the left hemisphere of the brain before syncope. The lateralisation precedes syncope and is associated with the onset of bradycardia, hypotension, and clinical symptoms. These findings suggest that the central nervous system may have a role in neurally mediated syncope.

Keywords: syncope; nervous system

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