Stroke-heart syndrome outcomes in pre-existing vs. new-onset dementia: a report from a global federated research network.

The prognostic significance of dementia onset in patients with stroke-heart syndrome (SHS) remains uncertain. We compared clinical outcomes between patients with pre-existing and new-onset dementia after ischemic stroke complicated by SHS. This retrospective cohort study used the TriNetX Global Collaborative Network, comprising de-identified electronic health records from more than 130 healthcare organizations between 2000 and 2024. Adults with ischemic stroke and subsequent SHS, defined as acute cardiac complications within 30 days after stroke, were identified and categorized as having pre-existing or new-onset dementia. Propensity score matching was used to balance demographics, comorbidities, and baseline treatments. Cox proportional hazards models estimated hazard ratios (HRs) with 95% confidence intervals. We identified 7,667 patients with pre-existing dementia and 22,375 with new-onset dementia. After matching, 7,667 pairs were analyzed. Compared with pre-existing dementia, new-onset dementia was associated with a higher 1-year risk of major adverse cardiovascular events (MACE; HR 1.13, 95% confidence interval 1.07-1.19). This excess risk was mainly reflected by recurrent stroke (HR 1.50, 95% CI 1.31-1.72) and heart failure (HR 1.34, 95% CI 1.23-1.47) among MACE components, while atrial fibrillation was also increased as a secondary outcome (HR 1.36, 95% CI 1.25-1.48). Findings were consistent at 2- and 3-year follow-up, among patients with first-ever stroke, and after further adjustment for NIHSS, thrombolysis, and post-stroke rehabilitation. Among patients with SHS, new-onset dementia was associated with higher cardiovascular risk than pre-existing dementia, supporting closer brain-heart-cognition monitoring after stroke.