Low (0–5) Alberta Stroke Program Early Computed Tomography Score on admission predictive of worse functional outcome after mechanical thrombectomy for anterior circulation large vessel occlusion

Domestic and foreign studies have validated the Alberta Stroke Program Early Computed Tomography Score (ASPECTS) as a standardized quantitative metric, reflecting the extent of infarction in instances of acute anterior circulation large vessel occlusion (ACLVO) [1, 2]. Recent reports have also demonstrated that this simple and reliable measure may serve to identify the most suitable patients for endovascular therapy and function as a prognostic index [3]. According to American Heart Association/American Stroke Association guidelines, the standard of care in adult patients with ASPECTS values ≥ 6 and large-vessel occlusion is endovascular therapy [4, 5]. However, much of the research on mechanical thrombectomy (MT) has excluded patients with lower ASPECTS values (≤ 6 or 7), failing to fully address the prognostic utility of ASPECTS in MT-treated patients [6, 7]. Only a few of patients with low ASPECTS accepted MT; therefore, data about their clinical outcomes remain scarce. In addition, whether MT is beneficial in AIS patients with low ASPECTS remains uncertain. Hence, in the present study, we compared ASPECTS values of NCCT studies on admission with clinical consequences of MT (including successful recanalization, functional improvement, symptomatic intracranial hemorrhage [sICH], and mortality), hoping to facilitate the planning of MT procedures.

Present findings indicate that ASPECTS values ≤ 5 on admission NCCT studies reduce the likelihood of long-term functional independence and increase the odds of sICH and mortality after MT in patients with ACLVO-related AIS. On the other hand, higher ASPECTS values (6–10) herald significantly better clinical outcomes and carry less risk of death. These associations proved significant in multivariate regression analysis, with other independent predictors emerging as well.

ASPECTS is a simple and convenient, topographic method of semiquantitatively gauging early ischemic core infarct volume and is deemed strongly predictive of clinical outcomes in the setting of AIS [1]. Typically, it is a stipulation for enrollment in various randomized intravascular treatment trials. Because past efforts seemed to restrict the merits of MT to patients with ASPECTS values ≥ 6, subsequent clinical trials have tended to exclude those with lesser scores [6, 7, 10]. Indeed, a recent meta-analysis of such studies undertaken by Phan et al. to explore ASPECTS as a basis for revascularization suitability has demonstrated the prognostic favorability of a higher (vs lower) ASPECTS status in the course of endovascular thrombectomy [10]. However, more and more efforts are showing that patients with lower ASPECTS values may well benefit from MT under certain conditions [11‐14]. In a subgroup analysis of the MR CLEAN randomized phase 3 trial, patients with ASPECTS values of 5–7 were regarded as acceptable candidates for endovascular therapy, otherwise weighing potential treatment benefit and cost-effectiveness of endovascular therapy (in conjunction with various influential factors) at values of 0–4 [3]. An analysis from the STRATIS Registry, conducted by Zaidat et al. and aimed at impacts of age and low (0–5) ASPECTS status (ie, large infarcts) on MT outcomes, has also revealed better clinical outcomes and lower risk of death in patients < 65 (vs > 75) years of age [13].

When comparing our two ASPECTS tiers (0–5 vs 6–10), there was no significant difference in rates of successful recanalization (mTICI scores > 2b). Yet, 90-day functional outcomes in low-scoring patients were better if vessel recanalization was achieved. In MT-treated patients with low ASPECTS values (0–5), Kaesmacher et al. have similarly linked successful recanalization to better outcomes and safety profiles [12]. Results of a meta-analysis by Cagnazzo et al. also suggested that patients with ASPECTS values of 0–6 may benefit from MT, with successful recanalization not only heightening the probability of long-term functional improvement but also reducing sICH occurrences. Still, only about one of four patients with ASPECTS values of 4 retained functional independence after MT, and just 14% had favorable functional outcomes at ASPECTS values of 0–3 [11].

Above findings are compatible with ours, rates of functional independence, sICH, and mortality for the two ASPECTS tiers (0–5 vs 6–10) being significantly different. ASPECTS determinations ≤ 5 also strongly signaled worse 90-day clinical outcomes in our multivariable logistic regression model (Table 4). Ultimately, ASPECTS status is a measure of infarct size, an apparent correlate of functional outcomes after endovascular reperfusion therapy [15, 16]. At lower scores, patients simply have less salvageable volumes of brain tissue and larger infarct volumes, both for shadowing functional deficits.

Until now, identifying patients who might benefit most from endovascular therapy after strokes has remained a serious question. According to our data, younger age, lower baseline NIHSS score, lower HbA1c concentration, and successful recanalization are all independent predictors of favorable outcomes after MT, regardless of ASPECTS status. These parameters are also aligned with reported findings in a series of endovascular therapy recipients [13, 17‐21].

For a variety of reasons, we did not examine diffusion-weighted imaging (DWI) or CTA studies in this cohort. NCCT remains the most accessible and economical diagnostic tool for emergency use in patients with strokes, and it is often all that time allows. Moreover, symptom severity or existing contraindications may prohibit DWI or CTA scanning procedures.

There are several limitations of this study worth mentioning. First, this was a single-center endeavor, with a relatively sparse sampling of low-scoring patients (ASPECTS 0–5) that may have skewed the results. In addition, all ASPECTS determinations were based entirely on NCCT images; and given the scarcity of patients with the lowest of scores (ASPECTS 0–3), comparative analysis within the lower ASPECTS tier (4–5 vs 0–3) was not feasible. Whether the lowest scoring patients (0–3) actually benefit from MT remains a topic for further study. The findings provided herein must be corroborated as well by multicenter prospective studies that entail other methods of examination.

ASPECTS values ≤ 5 signal worse long-term functional status (mRS scores > 2) in patients with ACLVO-related AIS undergoing MT. Older age, elevated HbA1c concentration, and higher baseline NIHSS score are other independent risk factors for poor clinical outcomes, whereas successful recanalization is protective of functional independence.