Author(s): HIRASAWA, A., HIRABUKI, K., TAKANO, D., SAKURAI, A., SUZUKI, R., FUKUIE, M., MURATA, H., MATSUSHIMA, S., HATA, N., MATSUDA, T., SHIBATA, S., Institution: KYORIN UNIVERSITY, Country: JAPAN, Abstract-ID: 823

INTRODUCTION:
Syncope arises from various etiologies; however, transient global cerebral hypoperfusion is considered a common underlying pathophysiological mechanism. The recurrence rate of non-cardiogenic syncope reportedly reaches 30–50% within three years after the first episode, and the cause of syncope often remains unidentified at initial clinical evaluation, making early prediction of recurrence risk a critical clinical issue. However, objective physiological markers capable of predicting syncope recurrence have not yet been established.
Dynamic cerebral autoregulation (dCA) plays a crucial role in maintaining stable cerebral blood flow against blood pressure fluctuations and may contribute to the pathophysiology of syncope. Nevertheless, the association between recurrent syncope and resting dCA, as well as potential age-related differences, remains unclear.
We hypothesized that resting dCA is impaired in patients with recurrent syncope compared with those experiencing a first episode, and that this impairment is more pronounced with aging. This study aimed to investigate the association between syncope recurrence and resting dCA and to evaluate the potential utility of dCA indices for predicting syncope recurrence.
METHODS:
Patients with syncope presenting to the emergency department were stratified by age and syncope history using a 2×2 factorial design: non-elderly (<65 years) vs elderly (≥65 years), and first-episode vs recurrent syncope. Accordingly, four groups were analyzed: non-elderly first-episode (n = 11, 42 ± 15 years, M/F = 6/5), non-elderly recurrent (n = 21, 37 ± 14 years, M/F = 5/16), elderly first-episode (n = 17, 77 ± 6 years, M/F = 12/5) and, elderly recurrent (n = 22, 77 ± 7 years, M/F = 17/5). Middle cerebral artery mean blood flow velocity (MCA Vmean) was measured using transcranial Doppler ultrasound, and mean arterial pressure (MAP) was measured noninvasively using a finger photoplethysmographic device (Finometer) for 3 min in the supine position. Offline analysis was performed to calculate transfer function gain between MAP and MCA Vmean in the very low-frequency (VLF) range (0.023–0.07 Hz), with higher gain indicating impaired dynamic cerebral autoregulation.
RESULTS:
Two-way ANOVA revealed significant main effects of age (P = 0.007) and syncope history (P = 0.047) on VLF gain, whereas no significant age × syncope interaction was observed (P = 0.114). In age-stratified analyses, VLF gain was significantly higher in patients with recurrent syncope than in those with a first episode in the non-elderly group (P = 0.030). In contrast, no significant difference was observed between syncope groups in the elderly group (P = 0.666).
CONCLUSION:
Impaired dynamic cerebral autoregulation may be associated with syncope recurrence in non-elderly patients but not in elderly patients. These findings suggest age-dependent differences in the relevance of dCA to syncope recurrence.