Mechanism of syncope: role of ambulatory blood pressure monitoring and cardiovascular autonomic function assessment.

Background And Aims: Identifying the haemodynamic mechanism of autonomic syncope is the essential pre-requisite for effective and personalized therapy aimed at preventing recurrences. The present study assessed the diagnostic efficacy of a two-step assessment.

Methods: Multicentre prospective, cross-sectional, observational study. Patients affected by severe autonomic syncope underwent a two-step assessment including 24-h ambulatory blood pressure monitoring and short cardiovascular autonomic function assessment (SCAFA). SCAFA consisted of carotid sinus massage (CSM), performed in patients ≥40 years old, a passive standing test, and a 'fast' head-up tilt test scheduled sequentially during one session on a tilt table.

Results: The study population consisted of 333 patients, 102 ≤ 40 years old and 231 > 40 years old. Any positive response was observed in 298 (89%) patients (92 [92%] in younger and 134 [89%] in older), with hypotensive phenotype accounting for 226 (68%), bradycardic phenotype for 21 (6%) and mixed phenotype for 51 (15%) of cases. The mean duration of the SCAFA procedure was 25 (IQR 20-32) min. Ambulatory blood pressure monitoring, CSM, passive standing, and head-up tilt test were positive in 60%, 15%, 3%, and 71% of patients, respectively. More than one test was positive in 51% and 49% of patients ≤40 and >40 years, respectively. Large inter-centre variability of CSM positivity rate, which remained significant after adjustment for demographic and clinical variables, was observed (P = .003).

Conclusions: The standardized 2STEPS protocol offers an easy-to-perform and time-saving diagnostic work-up allowing identification of the haemodynamic mechanism of loss of consciousness in most patients with autonomic syncope. This protocol provides the necessary background for a personalized mechanism-specific therapy.