Thrombolysis is known to improve outcomes following acute ischemic stroke. Intravenous thrombolysis using recombinant tissue-type plasminogen activator (rt-PA) is still considered the first line of treatment (1). However, the effect of thrombolysis is influenced by many factors.

Intracranial carotid artery calcification (ICAC) was first observed with radiographic pathology in the early 1960s (2). Later studies found that 69.4% of Chinese patients (3) and 82.2% of Dutch patients who were >55 years had ICAC on conventional head computed tomography (CT) (4). Vascular calcification is part of the atherosclerotic process and may indicates severe stenosis (5). Atherosclerotic calcification occurs in the form of hydroxyapatite deposits that resemble bone mineralization (6). The more advanced stages consist of calcified plaques. Confirmation of the coronary calcium score as a predictor of future cardiac events has spurred researchers' interest in ICAC. Recent clinical studies have demonstrated the risk factors for intracranial arterial calcification and its clinical significance (7). Studies have shown that intracranial vascular calcification is related to a higher risk of stroke independent of cardiovascular risk factors (8, 9). However, in contrast to the coronary vasculature, few studies have investigated the relationship between ICACs and the prognosis of patients with acute ischemic stroke (AIS) who receive intravenous thrombolysis (IVT) (10–13). And the conclusions of these studies are controversial. The question of whether atherosclerotic calcification might have distinct prognostic effects on stroke patients and therefore warrant specific treatment strategies still needs to be investigated.

In this context, we examined the relationship of the burden of ICAC with poor outcome, complications and mortality in patients treated with IVT for AIS. Studying the effect of ICAC on the prognosis of IVT in AIS may not only help to understand the relationship between ICAC and stroke, but also modify the acute management strategy, because ICAC information is usually available before treatment decision-making (13).

A total of 156 patients were included in the study. A total of 61 patients (39.1%) had a high calcification burden (HCB). A comparison of the baseline characteristics of HCB patients and LCB patients was summarized in Table 1. Compared with patients in the LCB group, patients in the HCB group had a higher incidence of atrial fibrillation (49.2 vs. 22.1%, P < 0.001) and coronary heart disease (24.6 vs. 10.0%, P = 0.019), and higher HbA1c (6.93 ± 1.77 vs. 6.37 ± 0.74, P = 0.023) and higher serum homocysteine levels (15.31 [12.15, 17.50] vs. 14.40 [11.20, 16.20], P = 0.036). Stroke etiology, admission clinical parameters and clinical outcomes of HCB patients and LCB groups were compared. The NIHSS score while admitted to the HCB group was significantly higher than that of the LCB group [8.00 (3.00, 16.50) vs. 5.00 (2.00, 10.00), P = 0.004]. The NIHSS score on the 7th day was significantly higher in the HCB group than the LCB group [5.00 (0.50, 12.50) vs. 1.00 (0, 4.00), P < 0.001], and the proportion of deterioration (deterioration in NIHSS ≥4) in the HCB group was higher than that in the LCB group (11.5 vs. 2.1%, P = 0.029). The mRS score of the HCB group was higher than that of the LCB group at 3 months [3.00 (0, 4.50) vs. 1.00 (0, 3.00), P < 0.001] (Table 2). The potential risk factors for ICAC were listed in Figure 2. After correction for other risk factors, atrial fibrillation (OR = 3.031, 95% CI: 1.312–7.006, P = 0.009) and HbA1c (OR = 1.488, 95% CI: 1.050–2.109, P = 0.026) were independent risk factors for ICAC. The interaction term model showed that the interaction between atrial fibrillation and HbA1c was not significant (OR = 1.459, 95% CI: 0.503–4.440, P = 0.469). Clinical characteristics associated with poor outcome, sICH, mortality were shown in Table 3. Univariate analysis showed that symptomatic side and total modified Woodcock score were associated with poor outcome [1.00 (0, 2.00) vs. 2.00 (1.00, 3.00), P < 0.001], [2.00 (0, 4.00) vs. 4.00 (2.00, 6.00), P < 0.001], sICH [1.00 (0, 2.00) vs. 2.00 (1.00, 3.00), P = 0.007], [2.00 (0, 4.00) vs. 4.00 (2.00, 6.00), P = 0.009] and mortality [1.00 (1.00, 2.00) vs. 3.00 (2.50, 3.00), P < 0.001], [2.00 (1.00, 4.00) vs. 6.00 (4.00, 6.00), P < 0.001] (Figure 3). In the multivariate logistic regression analysis, symptomatic side and total modified Woodcock score were independently associated with poor outcome (OR = 1.969, 95% CI: 1.220–3.178, P = 0.006 and OR = 1.354, 95% CI: 1.065-1.722, P = 0.013) and death (OR = 4.245, 95% CI: 1.114–16.171, P = 0.034 and OR = 2.414, 95% CI: 1.152–5.060, P = 0.020), but not with sICH (OR = 1.200, 95% CI: 0.700–2.057, P = 0.508 and OR = 1.093, 95% CI: 0.833–1.435, P = 0.521), as shown in Table 4.

The retrospective patient cohort study including 156 acute ischemic stroke patients who received intravenous thrombolysis analyses risk factors for ICAC and the prognostic value of high ICAC for functional decline, intracranial hemorrhage and all-cause mortality during 3 months follow-up. The main findings of the study were that atrial fibrillation and HbA1c were independent risk factors for ICAC and that total ICAC score and ICAC score of the symptomatic side predicted the outcomes of functional decline, intracranial hemorrhage and all-cause mortality.

Although our study found that ICAC was closely related to atrial fibrillation, whether there was a causal relationship between ICAC and atrial fibrillation was uncertain. Atrial fibrillation may be a downstream reaction of ICAC. It is generally believed that most patients with ICAC have coronary artery calcification, which is a risk factor for atrial fibrillation (19–21).

Previous studies have found that diabetes mellitus or random blood glucose are independent risk factors for ICAC (11, 22, 23). Although our study did not find a correlation between immediate blood glucose and ICAC, we found that elevated glycosylated hemoglobin was an independent risk factor for ICAC. Glycosylated hemoglobin is a biomarker of average glucose levels that can be used to follow hyperglycemia over the long term (24). Levels of glycosylated hemoglobin are a biomarker for vascular health (25). The relationships between high HbA1c and ICAC might be explained by the negative effect of poor glycemic control. Artery calcification may be caused by the accumulation of advanced glycation end products (26). The important driving factors of atherosclerotic calcification in diabetes include endothelial dysfunction, oxidative stress, changes in mineral metabolism, increased production of inflammatory cytokines and release of osteoprogenitor cells from bone marrow to circulation (27).

ICAC is a manifestation of vascular aging and a risk factor for acute cerebrovascular disease. However, there are few studies on the effect of thrombolysis and the prognosis of acute ischemic stroke. Vascular calcification can be divided into two different forms in morphology, depending on the location, namely, in the intima or media (28). The effect of carotid artery calcification on vascular remodeling and intimal injury is still unclear (29). Some studies have shown that ICAC can lead to vascular stenosis, thus affecting the pass rate and success rate of intra-arterial mechanical thrombectomy (30).

The effect of ICAC on intravenous thrombolysis is still unclear. Xin et al. (10) found that after correcting other risk factors, ICAC had no effect on the efficacy and prognosis of intravenous thrombolysis. However, Wu et al.'s (31) study suggested that ICAC may form microemboli after intravenous thrombolysis to embolize distant small vessels, resulting in a poor thrombolytic effect or aggravation of symptoms. Our study found that patients with HCB in the siphon segment of the internal carotid artery had a worse response to thrombolysis than patients with LCB. The proportion of patients with HCB whose NIHSS score increased more than 4 points after thrombolysis was higher than that of patients with LCB. This result is consistent with the studies of Lee et al. and Tábuas-Pereira et al. (11, 22).

Considering that calcification is a sign of more severe atherosclerosis, we can reasonably expect that increased arterial calcification would impair autoregulation and make blood vessels more likely to rupture. However, whether ICAC is a risk factor for intracerebral hemorrhage after thrombolysis is still controversial. Lin et al. (17) asserted that ICAC was a risk factor for intracranial hemorrhage after thrombolysis. However, studies by Lee et al. and Tábuas-Pereira et al. (11, 22) suggested that there was no correlation between ICAC and symptomatic intracranial hemorrhage. In our study, after correcting for other confounding factors, ICAC was not an independent risk factor for post-thrombolytic hemorrhage. The reasons for these differences may include the following: (1). The research methods used in each study had different calcification scoring standards; (2). Selection bias and the coexistence of other covariates were not considered in other studies; (3). The research found that patients with HCB have a higher proportion of atrial fibrillation, and cardiogenic cerebral embolism caused by atrial fibrillation was prone to postinfarction hemorrhage, and therefore, the existence of these confounding factors led to the deviation of the results; and (4). Another contributor may be the type of calcification, which was not distinguished in any of these studies.

The cycle of repeated rupture and healing of the plaque, accompanied by inflammation of the core and fibrous cap, leads to the presence of heterogeneity and calcified carotid plaque (32). In animal models, vascular calcification is related to the severity of arteriosclerosis. Vascular calcification and decreased vascular elasticity can make organs more susceptible to the impact of high blood flow and systolic pressure fluctuations, resulting in decreased vascular perfusion (33–35). ICAC can reflect systemic vascular calcification. The higher mortality rate of patients with HCB after thrombolysis may be related to the higher rate of cardiovascular calcification, including aortic calcification. High coincident calcification may be associated with ischemic event recurrence, including stroke and acute coronary syndrome recurrence. In our study, there was significant difference in the prevalence of coronary heart disease between the two groups, and the effect on recurrent coronary heart disease after stroke was uncertain. In our study, after adjusting for other confounders, ICAC was an independent risk factor for mortality after thrombolysis in stroke. ICAC was associated with all-cause mortality in our cohort.

Lee et al. (22) found that the proportion of patients with HCB whose mRS score was higher than two points at 90 days was higher, while some other studies (10–12) posited that complicated with ICAC was not related to the three-month prognosis. After correcting for confounding factors such as sex, age, atrial fibrillation, coronary artery disease, smoking, NIHSS baseline, and complications, we found that ICAC was still an independent risk factor for poor prognosis of acute ischemic stroke at 3 months after thrombolysis. In our study, we found that HCB was positively related to the basic NIHSS score, which is an independent risk factor for poor prognosis (36–39). However, after correction of the basic NIHSS score, HCB was still an independent risk factor for poor prognosis at 3 months.

An important strength is that only few studies have investigated the relationship between ICAC and the prognosis of patients with acute ischemic stroke who receive intravenous thrombolysis. Yet, our study has several limitations. First, we investigated the prognosis of patients at only 3 months after discharge; longer-term follow-up studies are needed in the future. Second, this was a single-center study, and there was inevitably selection bias. And the sample size is relatively small, especially the sample of sICH and mortality, which leads to the imbalance of sample size. This could have affected the meaningfulness of results obtained. All of these limitations will be addressed in future studies by using a larger sample size. Third, patients who underwent revascularization treatment or received conventional conservative treatment within 4.5 h of onset were not included in the study. We would consider including such patients in the next study. Fourth, undoubtly, the un-calcified plaques were also identified as risk factor to their prognosis. However, in the original design of the project, only calcified plaques were studied, and the number and size of un-calcified plaques were not counted. The interaction between those morphologic characteristics of plaques will be added in future studies. And the types of calcification were not distinguished in our study.

Our study showed that atrial fibrillation and glycosylated hemoglobin were independently associated with the prevalence of ICAC. ICAC was an independent risk factor for poor prognosis and mortality of cerebral infarction after intravenous thrombolysis. CT scans coupled with modeling algorithms will provide an objective marker for the prognosis of intravenous thrombolysis in acute cerebral infarction. Intervention of atrial fibrillation or control of high glycosylated hemoglobin may improve the prognosis of acute cerebral infarction after thrombolysis from another perspective.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Ethics Committee of the Yancheng Third People's Hospital. The patients/participants provided their written informed consent to participate in this study.

YS and ZD drafted the manuscript. YS, PP, and ZC participated in the literature collection. YS and GX analyzed the MRI features. HS and JZ reviewed and revised the manuscript. All authors read and approved the final manuscript.

This work was supported by the Research Project Fund of Clinical College of Jiangsu Medical Vocational College (20209127).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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