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

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.

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^-1) 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.

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).

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