Impact of blood viscosity on wake-up stroke: Analysis stratified by age and stroke subtype.

Objective: Ischemic stroke occurring during sleep is termed wake-up stroke (WUS). Dehydration increases blood viscosity (BV) and evokes thrombogenesis, a common cause of WUS. This study aimed to investigate the association between BV and WUS, stratified by age and stroke subtype.

Methods: The subjects were consecutive patients with acute ischemic stroke onset-to-door time within 72 h. Hematocrit-derived BV at a high shear rate (300 s) was calculated using hematocrit at admission. We assessed association of BV with WUS in the whole cohort, stratified by age (elderly group, ≥65 years; younger group, <65 years) and by stroke subtype (small-vessel occlusion [SVO], large-artery atherosclerosis [LAA], cardioembolism [CE]) stratified by age.

Results: We included 1362 acute ischemic stroke patients (975 [72 %] male, median age 69 years). WUS was observed in 326 (24 %) patients. Multivariable logistic regression in the whole cohort showed no association of BV with WUS (OR 1.163, 95 %CI 0.925-1.462, p = 0.197). Higher BV was significantly associated with WUS in the elderly group (OR 1.455, 95 % CI 1.080-1.959, p = 0.014) but not the younger group (OR 0.848, 95 %CI 0.568-1.268, p = 0.423). Among the stroke subtypes, higher BV was associated with WUS only in SVO (all ages: OR 2.316, 95 %CI 1.251-4.288, p = 0.008; elderly group: OR 2.427, 95 %CI 1.011-5.821, p = 0.047; younger group: OR 3.190, 95 %CI 1.131-8.544, p = 0.028).

Conclusions: Higher BV contributed to WUS in elderly patients. Among the stroke subtypes, higher BV was associated with WUS only in SVO.