P5678Near-infrared spectroscopy (NIRS) in the evaluation of psychogenic pseudosyncope - Moving towards a simplified diagnostic pathway
Authors: Claffey P , Perez-Denia L , Rivasi G , Ungar A , Finucane C , Kenny R A 
Published: October 2019

Abstract

Background
Psychogenic pseudosyncope (PPS) is a conversion disorder that often mimics syncope, is commonly referred to cardiology clinics and accounts for a large proportion of patients admitted with “unexplained syncope”. Unlike syncope, PPS is characterized by normal blood pressure (BP) and heart rate (HR) values at TLOC inferring the absence of cerebral hypoperfusion. The current gold standard for the diagnosis of PPS is the reproduction of patients' symptoms during a head-up tilt test (HUTT) with concurrent electroencephalogram (EEG) monitoring showing normal haemodynamic and brainwave measurements. However, EEG is time consuming, resource intensive and many syncope units lack ready access, thereby solely relying on absence of peripheral haemodynamic changes to diagnose PPS.

Purpose
Near-infrared spectroscopy (NIRS) is a non-invasive technology used for continuous monitoring of cerebral oxygenation. Measuring adequacy of tissue oxygenation is an appropriate surrogate for cerebral perfusion. In this study, we present a case series of patients for whom the diagnosis of PPS was confirmed by NIRS during TLOC. We propose use of NIRS in routine clinical assessment of suspected PPS.

Methods
We describe nine consecutive patients with suspected PPS referred to a dedicated syncope unit for investigation of recurrent unexplained syncope. All patients underwent evaluation in accordance with European Society of Cardiology guidelines including HUTT. Continuous beat-to-beat BP and HR measurements were recorded using finger plethysmography. In addition, continuous NIRS-derived tissue saturation index (TSI) - a measure of percentage oxygenation - was recorded using an optical sensor applied to the left lateral forehead to assess cerebral perfusion. Absolute values of BP, HR and TSI at baseline, time of first symptom onset, presyncope and apparent TLOC were recorded. The evaluation was diagnostic for PPS when apparent TLOC occurred in the absence of typical haemodynamic or cerebral perfusion changes.

Results
The median age was 35 years (range 14–54). Clinical features were consistent with those previously described in PPS literature - female preponderance, comorbid psychiatric diagnosis, frequent attack history, with prolonged TLOC and eyes closed during events. During HUTT, all patients experienced an apparent TLOC which they recognised as reproductive of typical events. BP and HR measurements increased significantly at time of TLOC. There was no significant change in TSI at any of the time points throughout HUTT. (Figure 1 shows averaged absolute values of systolic and diastolic BP, HR and TSI with median values represented by thickened lines.)
Figure 1. Measurements during HUTT

Conclusion
NIRS is readily available, easily accessible and provides an appropriate surrogate measure of cerebral perfusion during HUTT. We propose that HUTT incorporating concurrent NIRS monitoring will enhance diagnostic yield and patient management providing important biofeedback.