Predictive value of passive tilt-induced asystole for spontaneous syncope: insights froma single- centre ILR cohort

Background Tilt-induced asystole is considered a marker of cardioinhibitory syncope, but its predictive value for spontaneous events remains debated. Purpose To determine whether asystole during the passive phase of the tilt-table test (TTT) predicts spontaneous asystole documented by an implantable loop recorder (ILR), and to assess outcomes according to ILR-guided management. Methods This retrospective single-centre cohort (2015–2025) included adults with syncope and asystole ≥3 s occurring during the passive phase of a standard two-stage TTT protocol (70°, 20-min passive phase followed by nitroglycerin if negative). Patients whose first event occurred only after nitroglycerin were excluded. All subsequently underwent ILR implantation (median TTT-to-ILR interval 29.5 days [IQR 15.0–45.3]). ILR-documented symptomatic episodes were classified (blinded to TTT results) as bradycardia with asystole (pause ≥3 s), bradycardia without asystole, or normal rhythm. The primary endpoint was TTT–ILR concordance (positive predictive value, PPV). Secondary endpoints were 1-year syncope recurrence and outcomes according to therapy. Treatment was ILR-directed and included pacemaker (PM) implantation or cardioneuroablation (CNA); these were analysed as a single treated group. Results Among 74 patients (mean age 54.7 ± 14.4 years; 58.1% women), ILR follow-up averaged 21.6 ± 7.9 months. ILR recorded ≥1 symptomatic event in 54 (73.0%). ECG-based ILR mechanisms were bradycardia with asystole 19 (25.7%), bradycardia without asystole 23 (31.1%), and normal rhythm 12 (16.2%). TTT–ILR concordance for asystole was 25.7% (19/74). Among ILR-asystolic patients, 16 were treated based on ILR findings (13 PM; 3 CNA). At 1 year, syncope recurred in 12.5% of treated patients vs 46.6% in the non-treated group (RR 0.27, 95% CI 0.07–1.01; p = 0.019); all recurrences occurred in PM recipients. Conclusions Passive-phase TTT asystole predicted spontaneous asystole in only one in four patients, suggesting TTT may overestimate cardioinhibition. ILR-guided therapy markedly reduces recurrence.