In the present study, higher systolic SV was associated with poorer 3-month outcomes in patients with SIASO who were treated with IVT. An increase in systolic SV may thus predict a higher risk of poor outcome at 3 months (SV50%−75% [OR = 4.449, 95% CI = 1.231–16.075, p = 0.023], SV> 75% [OR = 8.676, 95% CI = 1.892–39.775, p = 0.005]). However, there was no clear relationship between systolic SV and END. Our findings may help physicians to identify patients with a relatively high risk of poor outcome at 3 months.
SV is an important index of BPV, and in our study it was associated with 3-month outcomes in AIS patients after IVT; this is consistent with the results of two previous studies [17, 24]. A study by Mei Yong et al.  in the European Cooperative Acute Stroke Study II trial revealed that high SBP variability is associated with poor outcome. Furthermore, an analysis from the Third International Stroke Trial (IST-3) reported an association between higher BPV and adverse events, the occurrence of symptomatic intracranial hemorrhage, and poor 6-month outcomes . However, none of these studies focused on patients with SIASO, and the IST-3 study only measured BP at three timepoints after IVT, while we measured BP hourly for at least 24 hours after IVT. Thus, the BPV in our study was likely more accurate than in other studies that measured BP less frequently.
The mechanism underlying the negative correlation between BPV and prognosis after IVT remains uncertain. Recent studies have reported that many patients have autonomic dysfunction after ischemic stroke [25–27]. BP fluctuation is a manifestation of autonomic dysfunction. During the early stage of ischemic stroke, a rapid increase in BP may cause intracranial pressure to rise and edema or bleeding to occur at the infarction site, which can lead to death or poor functional outcome . However, a large decrease in BP may lead to low perfusion in the infarct area; this effect might be much clearer in AIS patients with large-artery stenosis because patients with SIASO are very sensitive to BP fluctuations, especially in the first few hours after AIS [28, 29].
Cerebral autoregulation (CA) is the ability of the brain to regulate its own blood supply, which maintains an adequate and stable cerebral blood flow despite changes in cerebral perfusion pressure. However, CA is impaired after ischemic stroke, and this autoregulation is damaged in patients with intracranial arterial stenosis; furthermore, patients with more severe stenosis tend to have more severe dysautoregulation . One study reported that CA impairment ipsilateral to the AIS is associated with a larger infarction and poorer clinical outcome compared with patients with unimpaired CA ipsilateral to the AIS . With CA impairment, BP fluctuations have an important effect on cerebral blood flow. Moreover, when BPV increases to levels beyond the regulation of CA, it can lead to hypoperfusion or hyperperfusion in the infarction area.
Ischemic stroke is a clinical syndrome with a varied pathogenesis, including aortic atherosclerosis, small arterial occlusion, and cardiogenic embolism. BP fluctuations have different effects on ischemic stroke caused by different mechanisms . In China, 33–55% of ischemic stroke is caused by intracranial arterial stenosis or occlusion , and the prognosis of patients with this type of stroke is poorer than cerebral infarction with small vessel occlusion. BPV may be an indicator for risk stratification in this group of patients. In the present study, high SV in the early stage after IVT among patients with SIASO increased the risk of poor outcome at 3 months. This finding may help physicians to screen the most high-risk patients with poor prognosis from other high-risk patients at the early stage of AIS, and thus provide more appropriate interventions. However, we did not find any correlation between SV and END. Previous studies by other researchers have also failed to find a link between short-term outcomes (2-week outcome and in-hospital outcome), during the acute phase of ischemic stroke, and BPV [11, 32, 33].
SV, SD, and CV are three different indexes of BPV. In our study, there was only a relationship between SV and the 3-month outcome, while SD and CV were not associated with this outcome. Notably, SV is more commonly used in studies because it better reflects the time-series variability of BP. In contrast, SD and CV ignore temporal changes in the data, which can result in the same SD or CV in individuals with different clinical characteristics .
There were several strengths to our study. First, BPV was calculated by recording hourly BP within 24 hours after thrombolysis, which was far more frequently than in other studies and led to more accurate BPV results [11, 14]. Second, to the best of our knowledge, ours was one of the few studies to have focused on AIS patients after IVT and consider the effects of SAISO on prognosis. However, there were also several limitations in our study. First, the sample size was relatively small. Second, our study was a retrospective study. Third, magnetic resonance angiography was used to evaluate arterial stenosis in this study; however, this method is not as accurate as digital subtraction angiography for evaluating arterial stenosis, and might overestimate SIASO. Finally, intermittent cuff measurement was used to monitor BP in the present study, while continuous cuff monitoring or invasive arterial BP are more accurate.