| Summary: | <h4>Introduction</h4>Prior use of direct oral anticoagulants has been associated with reduced stroke severity in patients with non-valvular atrial fibrillation (NVAF). The aim of this study was to investigate the impact of prothrombin time (PT) and activated partial thromboplastin time (aPTT) on stroke severity in patients who were receiving dabigatran or rivaroxaban at the time of stroke onset.<h4>Materials and methods</h4>We enrolled 107 patients with NVAF who developed acute ischemic stroke while on dabigatran or rivaroxaban and presented within 24 hours to nine hospitals between January 2014 and December 2018. The results of PT and aPTT assays were obtained within 24 hours of stroke onset in all patients. We analyzed PT and aPTT in relation to stroke severity and ischemic lesion volume using correlation and multivariable regression analyses.<h4>Results</h4>Of the 107 patients included, 46 (43.0%) were on dabigatran and 61 (57.0%) were on rivaroxaban. In patients with prior dabigatran use, while aPTT was inversely correlated with admission National Institutes of Health Stroke Scale (NIHSS) score (r = -0.369, p = 0.012) and ischemic lesion volume (r = -0.480, p = 0.005), there was no correlation between PT and either of these variables. Multivariable analysis confirmed the existence of a significant independent inverse relationship between aPTT and NIHSS score at admission (B, -0.201; 95% confidence interval [CI], -0.370 to -0.032; p = 0.005) and between aPTT and ischemic lesion volume (B, -0.076; 95% CI, -0.130 to -0.023; p = 0.007). In patients with prior rivaroxaban use, neither PT nor aPTT was associated with admission NIHSS score or ischemic lesion volume in the correlation and multivariable analyses.<h4>Conclusions</h4>In patients with NVAF who were receiving dabigatran, prolonged aPTT was associated with reduced stroke severity.
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