Time to diagnosis and predictors of positive diagnostic findings in patients with unexplained syncope undergoing implantable loop recorder monitoring

Background Implantable loop recorders (ILRs) are widely used for evaluating patients (pts) with syncope who remain undiagnosed after initial non-invasive testing. However, diagnosis may take considerable time after ILR implantation. Identifying baseline characteristics associated with earlier diagnosis may help optimize follow-up. Objective To analyze time-to-diagnosis (TTD) after ILR implantation for syncope and identify predictors of earlier diagnosis in a real-world population from a local health unit in Portugal. Methods Single-center retrospective cohort study including pts monitored with ILR (Dec 2014-Dec 2024). Baseline clinical, electrocardiographic and echocardiographic findings were collected. The subgroup of pts who received ILRs for syncope was analyzed. Positive diagnostic findings included symptomatic sinus node disease (SND), atrioventricular (AV) node disease (high-grade AV block (AVB); complete AVB), new-onset atrial fibrillation (AF), slow AF (symptomatic ventricular pause >3s) and sustained supraventricular (SVT) or ventricular tachycardia (VT). Pts with a positive diagnosis (group 1) were compared with those without (group 2). TTD was analyzed using Kaplan–Meier curves, and differences between groups were assessed with the log-rank test. Cox regression was applied to identify independent predictors of earlier diagnosis. Results Overall, 274 pts underwent ILR implantation for unexplained syncope (146 male, 53.3%; mean age 67±16 years). A total of 91 pts had a positive diagnosis (33.2%), with a median TTD of 6 months. The most frequent findings were symptomatic SND (n=43, 47.3%) and complete AVB (n=16, 17.6%) (Figure 1A). Group 1 more often had hypertension (64.8 vs 50.6, p=0.026). Regarding baseline electrocardiogram, group 1 had a longer median QRS duration (105 [87-123] vs 91 [75-107]ms, p=0.028) and a higher prevalence of bundle branch block (BBB) (23.9 vs 11.7%, p=0.029). There were no differences in left ventricular ejection fraction (63 vs 60%, p=0.089) or ventricular sensing parameters at implant (0.58±0.22 vs 0.71±0.45mV, p=0.387). Kaplan-Meier analysis for TTD revealed a significantly shorter diagnostic time in pts with baseline conduction abnormalities (BBB: p=0.002; left BBB (LBBB): p=0.005; right BBB (RBBB)+ left anterior fascicle block (LAFB) combined w first-degree AVB: p<0.001) (figure 2). In multivariable Cox regression, only RBBB+LAFB+ first-degree AVB remained an independent predictor of earlier diagnosis (HR 4.18, 95% CI 1.33–13.16, p = 0.014) (Figure 1B). Conclusion In this cohort, the median TTD during ILR monitoring for syncope was 6 months. Baseline conduction abnormalities were associated with a significantly shorter TTD.