Association Between Meteorological Variables and Emergency Department Presentations for Syncope: A Five-Year Retrospective Time-Series Study

<title>Abstract</title> <p>Background Syncope is a frequent reason for emergency department presentation and may be influenced by environmental, seasonal, behavioral, and physiological factors. Heat exposure, humidity, atmospheric pressure changes, and short-term weather variability have been suggested as potential triggers for fainting and orthostatic intolerance; however, the evidence remains limited and inconsistent. This study aimed to investigate the association between daily meteorological variables and emergency department presentations for syncope over a five-year period. Methods We conducted a retrospective time-series study including all patients who presented to the emergency department with a complanit of syncope between January 2021 and December 2025. Daily syncope case counts were extracted from hospital records and merged by date with meteorological data obtained from the Şişli/18401 meteorological station. The evaluated meteorological variables included temperature, relative humidity, atmospheric pressure, precipitation, and wind speed. Lagged and derived variables were calculated to assess delayed and short-term change effects. Lag-1 and lag-2 values were computed for temperature and atmospheric pressure, lead-1 values were explored descriptively, and daily change variables were calculated as differences between consecutive days. Syncope-positive days were defined as days with at least one syncope presentation. Univariate comparisons were performed using two-sample t-tests and Wilcoxon rank-sum tests. Spearman rank correlations were calculated across lag windows from − 3 to + 3 days. Multivariable negative binomial regression was used to model daily syncope counts, and logistic regression was used to model the occurrence of at least one syncope presentation per day. Both models included meteorological variables, daily change variables, season, and calendar year. Generalized additive models with a negative binomial family were used to assess potential non-linear associations. Results During the 1,826-day study period, 722 syncope presentations were recorded on 564 days. The mean daily number of syncope cases was 0.40, with a range of 0–4 cases per day. Syncope-positive days accounted for 30.9% of all study days. Mean temperature was 16.8°C on syncope days and 16.4°C on non-syncope days. Mean atmospheric pressure was also similar between syncope and non-syncope days. In univariate analyses, none of the same-day, lagged, or lead meteorological variables showed a statistically significant association with syncope occurrence. Spearman correlations between meteorological variables and daily syncope counts were uniformly weak across all examined lag windows.</p>