AIS results from a thrombus or embolus block in the cerebral arteries and accounts for a large proportion of all strokes [1, 2]. Early thrombolysis for acute cerebral infarction is a safe and reliable option, but it may have risk [9, 11–13]. Accurately identifying the risk factors for adverse outcomes in AIS patients after IV thrombolytic therapy to timely adjust clinical strategies is crucial for clinical patient management. This study is based on the overall data of two advanced stroke centers that involved factors related to IV thrombolytic therapy. The thrombolytics included rt-PA and domestic UK. Univariable and multivariable analyses were performed to screen out the variables related to the target variable, namely the adverse outcome after IV thrombolytic therapy in AIS patients. By comparing the OR values and their 95% CI, risk factors and protectors were identified. The results suggest that ECG, CHOL, NIHSS, CT, and Doppler ultrasound could predict unfavorable neurological functional outcomes after thrombolysis for AIS. Antiplatelet therapy reduces the risk of unfavorable outcomes.
The increasing age of patients has an important impact on the incidence, mortality, and long-term stroke outcome [30]. Rejno et al. [31] suggested that age could predict the deterioration of neurological functions after stroke. It may be because advanced age leads to the dysfunction of neurovascular units and neurodegenerative changes in stroke patients [32]. In the present study, age was a risk factor for adverse outcome after IV thrombolytic therapy (OR = 1.101, 95%CI = 1.048–1.157), and its clinical significance was that for every increase in one year of age, the risk of in-hospital adverse outcome was increased by 10.1% for AIS patients undergoing IV thrombolytic therapy. NIHSS2 was a risk factor for adverse outcomes after IV thrombolytic therapy (OR = 1.336, 95%CI = 1.235–1.444), and the clinical significance was that for every point increase in the NIHSS score immediately after thrombolytic therapy, the risk of in-hospital adverse outcome was increased by 33.6% after IV thrombolytic therapy. Therefore, the relationship between the variables age and NIHSS2 and the outcome in the present study was consistent with previous findings.
The correlation between blood lipids and stroke outcome varies depending on the components of blood lipids. CHOL is a modifiable risk factor, and CHOL levels are closely associated with the first ischemic stroke attack [33]. Globally, since 1990–2013, high cholesterol levels (greater than 185 mg/dl) have led to a 24% increase in stroke-related disability-adjusted life years [34]. CHOL levels are positively correlated with the risk of ischemic stroke. Celap et al. [35] found that APOA5 genotype (TC + CC) was more common in patients with NIHSS score ≥ 21, suggesting that APOA5 genotype (TC + CC), age, and obesity can be used as risk factors for outcomes in extremely severe stroke patients (NIHSS ≥ 21). In the present study, CHOL was a risk factor for adverse outcomes after IV thrombolytic therapy (OR = 2.51, 95%CI = 1.432-4.4). Its clinical significance was that for every increase in CHOL by 1 mmol/L, the risk of adverse outcomes after IV thrombolytic therapy was increased by 151%. The correlation between CHOL and outcome in the present study was consistent with that of previous findings.
HDL-C is a powerful and independent negative predictor of cardiovascular and cerebrovascular diseases. The beneficial effect of HDL is largely due to its key role in reverse cholesterol transport, namely the transport of excess cholesterol in peripheral tissues to the liver. There is increasing evidence that HDL also has anti-inflammatory, antioxidant, and vasodilator characteristics, reducing atherosclerosis [36]. Gu et al. [37] surveyed six cohort studies involving 267,500 Chinese subjects and showed that LDL-C and TG levels were positively correlated with ischemic stroke, while HDL-C levels showed a negative correlation. Li et al. [38] suggested that the ATP-binding cassette transporter A1 (ABCA1)/apolipoprotein E (ApoE)/HDL signaling pathway may be involved in the myelination and oligodendrocyte cytogenesis of ischemic brain tissues after stroke, which could repair the white matter damage of the central nervous system caused by stroke and promote the white matter remodeling of ischemic brain tissues, thereby facilitating the recovery of neurological function in the late stage of ischemic stroke. Hence, HDL is associated with the functional outcome of ischemic stroke and might be a protector for the outcome. In the present study, HDL was a protector for adverse outcomes after IV thrombolytic therapy, which was consistent with previous findings. After multivariable analysis, the OR value of HDL was 0.047, 95% CI = 0.005–0.488. The clinical significance was that for every increase in HDL by 1 mmol/L, the risk of adverse outcomes after IV thrombolytic therapy was reduced by 95.3%.
ApoA1 is the main lipoprotein related to HDL in plasma and the main protein component responsible for the transport of cholesterol in HDL [39], which plays an important role in reverse cholesterol transport. ApoA1 has clinical value in the diagnosis of ischemic stroke and differentiation from hemorrhagic stroke [40]. A meta-analysis showed that decreased ApoA1 levels and increased ApoB/A1 ratio were risk factors for ischemic stroke [41]. Studies have found that serum ApoA1 levels are negatively correlated with the prevalence of type 2 diabetes and fasting venous blood glucose levels [42]. The latter two are also common clinical risk factors for cerebrovascular diseases. Previous studies have suggested that ApoA1 levels might be associated with the occurrence of atherosclerotic cerebral infarction and the characteristics of carotid plaque [43]. Ohtani et al. [43] showed that compared with the normal control group, ApoA1 levels in patients with atherosclerotic stroke were significantly reduced. The serum ApoA1 levels of the low-intensity plaque subgroup were significantly lower than those of the medium-intensity plaque subgroup and the high-intensity plaque subgroup. In addition, the serum ApoA1 level of the mixed plaque subgroup was significantly lower than that of the simple plaque subgroup. ApoA1 is shown to enhance the excretion of cholesterol from arterial wall cells and prevent atherosclerosis [44]. The present study found that ApoA1 was a protector for the adverse outcome of AIS patients after IV thrombolytic therapy (OR = 0.034, 95%CI = 0.002–0.573), and its clinical significance was that for every increase in the ApoA1 level by 1 g/L, the risk of adverse outcome after IV thrombolytic therapy was reduced by 96.6%, which was consistent with previous findings.
IV thrombolytic therapy and endovascular thrombectomy can quickly achieve reperfusion to reduce disability [9, 11–13, 45]. Still, IV thrombolytic therapy has an increased risk of symptomatic intracerebral hemorrhage (sICH) [46]. Non-contrast CT can exclude intracranial hemorrhage, and it is crucial to recheck the head CT as soon as possible after thrombolysis (after 24 h, and before the administration of antiplatelet drugs) [9]. In the present study, CT2 was a risk factor for the outcome (OR = 3.308, 95% CI = 1.325–8.26), and its clinical significance was that the risk of adverse outcome in patients with intracranial hemorrhage on CT scan 24 h after IV thrombolytic therapy was 3.308 times that in those without intracranial hemorrhage, which was consistent with previous findings.
ECG plays an important role in identifying risk factors for stroke, such as atrial fibrillation and left ventricular hypertrophy. Cardiogenic stroke caused by atrial fibrillation accounts for one-third of ischemic strokes [1, 2]. The role of atrial fibrillation in cryptogenic stroke is well-known. In about 25% of patients with ischemic stroke, new atrial fibrillation can be noted through routine enhanced ECG monitoring [47]. Lowres et al. [48] studied the use of iPhone ECG (iECG) in pharmacies for a community screening of unknown atrial fibrillation. They found that the high risk of stroke/thromboembolism in newly confirmed atrial fibrillation patients could be largely prevented. Many other ECG characteristics, namely ECG/structural remodeling-Q wave, QRS/QT interval, bundle block, P wave interval/amplitude/dispersion, other waveform angles and slopes, higher automatism, ectopic beats, atrial tachyarrhythmia, and heart rate and its variability, are also potential predictors for stroke [49]. Gatti Pianca et al. [50] evaluated the relationship between ECG p-wave abnormality and neurological dysfunction in patients with cryptogenic stroke and found that in the ECG criteria, left atrial enlargement assessed by clockwise rotation was more common in disabling stroke. In the present study, ECG was a ranked variable. When setting dummy variables, the first grade-normal ECG was used as the reference and the second grade-mild change as the risk factor for the outcome. The OR value was 17.532 (95%CI = 1.765-174.178), and the clinical significance was that the risk of adverse outcomes in patients with mild ECG changes before IV thrombolytic therapy was 17.532 times that of patients with normal ECG. The third grade-malignant arrhythmia was associated with adverse outcomes (OR = 25.213, 95%CI = 2.219-286.425). Its clinical significance was that the risk of adverse outcomes in patients with malignant arrhythmia in ECG before IV thrombolytic therapy was 25.213 times that of patients with normal ECG. The results of the ranked variables suggested that the impact of each grade on the outcome was not equidistant.
Lower extremity venous thrombosis is severe comorbidity of ischemic stroke. Paralysis after stroke is a common cause of lower extremity venous thrombosis. Pan et al. [51] used some clinical characteristics and accessible biochemical parameters to develop and validate a nomogram for predicting the risk of deep vein thrombosis in patients with acute stroke within 14 days. Liu et al. [52] conducted a study on 679 stroke patients (including 507 with ischemic stroke and 172 with hemorrhagic stroke) and found that 21.1% of patients with ischemic stroke (n = 107) were affected by deep vein thrombosis. The intermuscular veins, especially the fibular veins, were the most susceptible. Ha et al. [53] studied Asian AIS patients with lower extremity deep venous thrombosis and found that female and higher NIHSS scores were independently associated with lower extremity deep venous thrombosis. Compared with D-dimer screening, lower extremity deep venous color Doppler ultrasound of patients with severe neurological deficits might be more conducive to diagnosing deep vein thrombosis in Asian AIS patients. Decreased activities of the lower extremities or joint contractures caused by stroke and other reasons may be the main contributors to deep vein thrombosis of the lower extremities, which can further lead to a prolonged rehabilitation process [54]. After completing the acute phase of treatment, most stroke patients need rehabilitation. It usually takes months or even years for patients to restore their extremity function fully. Paralyzed limbs may be restricted in daily activities such as turning over, getting up, and moving short distances due to decreased activities. After lower extremity venous thrombosis, the rehabilitation exercise of the paralyzed limbs will be further decreased, which will lead to a longer recovery time of the extremity function, and severe neurological deficits, and poor outcome. Therefore, lower extremity venous thrombosis may be a risk factor for poor outcomes after stroke. The present study found that lower extremity venous color Doppler ultrasound was a risk factor for the outcome (OR = 5.685, 95% CI = 1.850-17.471), and its clinical significance was that the risk of adverse outcome in patients with lower extremity venous thrombosis revealed in the lower extremity venous color Doppler ultrasound after IV thrombolytic therapy was 5.685 times that of patients without lower extremity venous thrombosis.
Antiplatelet therapy with drugs such as aspirin is one of the traditional therapies for treating ischemic stroke. Aoki et al. [55] showed that aspirin combined with IV thrombolytic therapy and endovascular treatment played a key role in reducing stroke recurrence. The current domestic and foreign AIS and TIA treatment guidelines strongly recommend antiplatelet regimen using aspirin for antiplatelet aggregation therapy [56–58]. Chinese guidelines for diagnosis and treatment of AIS 2018 recommended that aspirin be administrated within 48 h of stroke onset for patients who do not meet IV thrombolytic therapy or endovascular thrombectomy indications and have no contraindications. The AIS management guidelines issued by the American Heart Association/ASA in 2018 clarified the Class IIa recommendation for dual antiplatelet drugs for the treatment of acute minor stroke [59, 60]. From several prospective randomized controlled trials such as the CHANCE [61] and POINT [62] trials, aspirin combined with clopidogrel can significantly reduce the neurological deterioration in patients with acute non-cardiogenic stroke. A meta-analysis of 16 randomized controlled trials involving 28,032 patients showed that dual antiplatelet therapy was significantly superior to single antiplatelet therapy in reducing the incidence and mortality of stroke and its composite events (i.e., cardiovascular diseases), but bleeding events did not increase significantly [63]. Dual antiplatelet therapy may exert synergistic effects by inhibiting different platelet pathways. The variable antiplatelet in the present study was a ranked variable and a protector for the outcome. With the first grade, namely no anti-platelet aggregation treatment as the reference, the OR value of the second grade was 0.089, 95% CI = 0.033–0.237. Its clinical significance was that the risk of adverse outcomes in AIS patients receiving anti-platelet aggregation treatment with aspirin alone within 24–48 h after IV thrombolytic therapy was decreased by 91.1% compared with that in those receiving no anti-platelet aggregation treatment. The OR value of the third grade was 0.063, 95% CI = 0.014–0.289, and suggesting that the risk of adverse outcome in AIS patients receiving anti-platelet aggregation treatment with two drugs (one of which was aspirin) within 24–48 h after IV thrombolytic therapy was decreased by 93.7% compared with that in those receiving no anti-platelet aggregation treatment, which was consistent with previous findings.
Regarding the strategies of screening variables into the multivariable regression, the baseline variables considered clinically relevant, or the baseline variables that had a univariable relationship with the outcome were included in the multivariable risk regression model [64]. Given the number of available events, and to ensure the conciseness of the final model, the variables were carefully selected. As candidate variables that might impact the outcome event, first, from the perspective of clinical specialty, its role must be acceptable to people, and it can be reasonably explained from a certain physiological mechanism or pathway. The candidate variables of the present study included demographic data (e.g., sex, age, and BMI, lifestyle (e.g., smoking and drinking), medical history (e.g., hypertension, diabetes, coronary heart disease, arrhythmia, hyperlipidemia, and past stroke), examinations (blood test indicators and other examination items), treatments (thrombolytics type, DNT, and OTT time), and exposure/treatment factors (NIHSS score after thrombolysis, subsequent related antiplatelet, anticoagulation, lipid regulation, and rehabilitation). For the above candidate variables, by referring to the previously published literature, the published and reported variables that had independent effects on the outcome event were summarized and used as key candidate variables for alternatives.
Second, the variables were screened from the results of the univariable analysis. The relationship between traditional univariable analysis and univariable regression analysis was essentially equivalent. Univariable analysis analyzed the differences of single factors among groups and included the t-test, chi-square test, and analysis of variance. Through these univariable analysis methods, distribution differences of the means or percentages between two or among multiple groups can be simply and directly observed. Univariable regression analysis included only one factor into the regression model for fitting when constructing the regression model. Therefore, univariable regression analysis was equivalent to the traditional univariable analysis methods used in the present study. The t-test was equivalent to simple linear regression, while analysis of variance was equivalent to multiple linear regression. Similarly, the results of the analysis of variance and the univariable linear regression were also consistent to a certain extent. Not only the results of univariable linear regression were consistent with the results of the t-test and analysis of variance, the results of univariable logistic regression and chi-square test were also equivalent. Therefore, during screening variables in the present study, the chi-square test was used to conduct univariable analysis of categorical variables and ranked variables, which was essentially equivalent to univariable regression analysis, and the P values obtained were equivalent and effective. The present study used the Mann-Whitney U-test for non-normally distributed continuous variables and used the general linear model - univariable test method for normally distributed ones. The latter was essentially equivalent to a two independent-sample t-test. The test method used for continuous variables was essentially equivalent to the univariable regression analysis. The P values obtained were also equivalent and effective.
Given in the univariable analysis, the differences among the results did not reflect the effect of the factor on the outcome event, statistically significant variables in the univariable analyses (P < 0.05) were used as the first echelon of candidate variables, and the inclusion criteria were appropriately extended to P < 0.20 [65], effectively avoiding the omission of some important variables. Although they were not statistically significant in the univariable analysis, their real effects might be underestimated or neglected due to the limitation of the P-value. In addition, the variables with P-value close to 0.2 were carefully considered, incorporating the relevance to the clinical professional background and requirements of the sample size for the number of independent variables screened. For logistic regression, the number of positive outcome events should be at least 15–20 times the number of independent variables finally screened.
When performing multivariable regression analysis, categorical variables with three categories and above need dummy variables because parametric regression was made, which was in the framework of a generalized linear model, and the latter was essentially a linear trend. If there were no dummy variables and the categorical variables with three categories and above were directly included in the multivariable adjustment, then the relationship among the categories had equivalent effects on the outcome during the statistical analysis. It was a linear relationship, but it was a very narrow control of an equidistance. Still, many medical variables were multi-categorical variables, and there was no such equidistant relationship. In order to better explain which variable had a greater impact on the outcome, a reference must be set, namely the dummy variable.
The outcome-related variables screened in the present study conformed to the clinical practice. The severity of stroke can be assessed on a clinical basis according to the degree of neurological deficits (for example, disturbance of consciousness, language and behavioral disorders, visual field defect, dyskinesia). Many studies have conducted quantitative measurements of neurological deficits, and NIHSS scores are increasingly used in clinical practice for assessment. Although many previous studies have shown that the NIHSS score is a reliable predictive tool for the outcome of stroke, which can be used to compare the changes in neurological functions after IV thrombolytic therapy in AIS patients to assess the efficacy [66], its relationship with the outcome varies with the time after the onset of cerebral ischemia [28]. It may be because many patients have undergone a gradual recovery process, and the early symptoms of stroke-related deficits are often changeable. Therefore, NIHSS scores associated with specific disability outcomes tend to shift to lower scores over time. In addition, the correlation between NIHSS score and disability in late-stage is increased over time. Some studies have found that the optimal predictor of poor outcome 24 h after ischemic stroke is NIHSS score > 22, and the optimal predictor in days 7–10 is NIHSS score > 16 [28, 29].
The present study has some limitations. First, the follow-up was short. Future studies can extend the follow-up time to 3 months to half a year after the onset of ischemic stroke. Second, the sample size should be increased using data from multiple centers.
In conclusion, ECG at admission could predict unfavorable neurological functional outcomes after IV for AIS patients. CHOL, NIHSS score immediately after thrombolysis, head CT revealing intracranial hemorrhage 24 h after thrombolysis, and lower extremity venous color Doppler ultrasound showing venous thrombosis of lower limbs can also predict the risk of unfavorable outcomes. Antiplatelet therapy may help develop treatment strategies and reduce the risk of unfavorable outcomes.