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Abstract
Background Favorable imaging profile according to the Alberta Stroke Program Early CT Score (ASPECTS) on non-contrast head CT is a key criterion for the selection of patients with ischemic stroke from large vessel occlusion (LVO) for IA revascularization therapies.
Objective To analyze factors associated with changes in ASPECTS during inter-hospital transfer and to determine how deterioration of ASPECTS affects eligibility for endovascular procedures.
Methods We analyzed factors associated with changes in ASPECTS during inter-hospital transfer and their potential impact on eligibility for IA stroke therapies in patients with anterior circulation ischemic strokes. Clinical and demographic characteristics between patients with favorable (ASPECTS ≥6) and unfavorable (ASPECTS <6) imaging on repeat CT were compared.
Results Stroke evolution towards unfavorable ASPECTS occurred in 13/42 (31%) patients who initially had a favorable imaging profile at outside hospitals. A higher National Institutes of Health Stroke Scale (NIHSS) score was the only significant predictor of ASPECTS decay, whereas other clinical characteristics, such as the use of IV thrombolysis and site of LVO, were similar between the two groups.
Conclusions In our cohort, one out of three patients became ineligible for IA thrombectomy because of unfavorable ASPECTS ‘decay’ following inter-hospital transfer. Except for NIHSS severity, baseline clinical factors could not identify which patients were at risk for ASPECTS deterioration.
- Thrombectomy
- CT
- Stroke
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Introduction
Based on the results of the recent randomized trials of endovascular stroke therapy, updated guidelines on early management of patients with acute ischemic stroke, emphasizing the importance of rapid transport of eligible patients to centers capable of performing endovascular stroke treatment, were released by the American Heart Association (AHA).1 Key selection criteria when considering potential candidates for intra-arterial thrombectomy include documentation of large vessel occlusion (LVO), favorable imaging profile according to Alberta Stroke Program Early CT Score (ASPECTS) on non-contrast head CT, and time from symptom onset to treatment.1
ASPECTS is a 10-point scoring system of early ischemic changes in 10 distinct anterior circulation brain regions and serves as a strong predictor of outcome following thrombectomy; patients with a higher ASPECTS score are more likely to achieve a favorable outcome and have a lower chance of intracranial hemorrhage after IA stroke therapy than patients with a lower score.2–4 The updated AHA guidelines currently recommend endovascular therapy in patients with ASPECTS ≥6.1 Previous research demonstrated that the rates of ASPECTS decay during inter-facility transfers correlate with clinical outcomes in patients who receive endovascular stroke interventions at the accepting facility.5 The goal of our study was to analyze factors associated with changes in ASPECTS during inter-hospital transfer and to determine how deterioration of ASPECTS affects eligibility for endovascular procedures.
Methods
The study was approved by our local institutional review board. We retrospectively reviewed cases of patients with acute ischemic stroke who were transferred to our comprehensive stroke center from outside facilities between January 2012 and December 2014. Cases with acute ischemic stroke from anterior circulation LVO were included in analysis. LVO was defined as occlusion of the intracranial portion of the internal carotid artery or the M1/2 segments of the middle cerebral artery.
The following data were collected: age, gender, cerebrovascular risk factors, time of symptom onset (or time patient last known at baseline if exact time of onset was unknown), IV tissue plasminogen activator use at outside hospital, time of initial non-contrast CT at outside hospital, and repeat CT at our hospital. Cases in which non-contrast CT studies from an outside hospital were unavailable for review were excluded from analysis. ASPECTS values were independently evaluated by two reviewers (MM and SS) who were trained on ASPECTS scoring (http://www.aspectsinstroke.com/training-for-aspects/test/) and were blinded to the timing of the studies. Any disagreements about scores were resolved by consensus. A favorable ASPECTS profile was defined as ASPECTS ≥6, and unfavorable, ASPECTS <6, based on the imaging criteria proposed by the AHA in the 2015 updated acute stroke guidelines.1 Analysis of variables was performed using Fisher's exact test for categorical data and a two-tailed t test for continuous data. For all statistical analyses, p<0.05 was considered statistically significant.
Results
During the study period, 236 patients with a diagnosis of acute ischemic stroke were transferred to our hospital from outside hospitals. Upon arrival at our institution, LVO was diagnosed on emergent non-invasive imaging in 58 (25%) of transferred patients. Of those, 50 patients with qualifying LVO were included in the final analysis. Average time from symptom onset to first (outside) CT was 521±309 min. The median ASPECTS on first CT was 9 (IQR 8–10). Assuming that at stroke onset all 50 patients had ASPECTS of 10, the score of the entire cohort deteriorated by 1 point before the first CT was obtained.
Of the 50 transferred patients with anterior circulation LVO, 42 had favorable ASPECTS ≥6 on CT imaging performed at an outside hospital. Nineteen (45%) of those 42 patients presented to an outside facility within 6 h of stroke onset (mean time from symptom onset to head CT, 295±61 min), whereas in 23 (55%) patients CT showed favorable ASPECTS with stroke onset beyond the 6 h window (mean time from symptom onset to outside CT, 603±224 min).
The average time between obtaining an outside CT to a repeat CT at our hospital was 280±99 min. On repeat CT imaging at our hospital, 21 patients had ASPECTS <6. Therefore, stroke progression towards unfavorable ASPECTS occurred in 13 (31%) of the 42 patients who initially presented to an outside hospital with a favorable score (table 1). Higher baselines National Institutes of Health Stroke Scale (NIHSS) was seen in patients who demonstrated unfavorable ASPECTS on repeat imaging at out hospital than in patients in whom ASPECTS remained within the 6–10 range after inter-hospital transfer (17.2±4.4 vs 13.2±5.1, p=0.018). Time from outside CT to repeat CT at our hospital was, on average, 57 min longer in patients with unfavorable ASPECTS than in those with favorable ASPECTS on repeat imaging, although this difference did not reach statistical significance (p=0.14). There was no significant difference in demographic data, blood pressure parameters, use of IV tissue plasminogen activator before transfer, or site of LVO between the two groups (table 1).
Analysis of ASPECTS decay during inter-hospital transfer in patients with favorable (ASPECTS≥6) at outside hospital, n=42
Of the 42 patients with favorable ASPECTS on initial CT, 28 were transported to our institution by air (mean time between the initial and repeat CT was 268±65 min), and 14 over ground by ambulance (mean time 311±141 min, p=0.31).
Discussion
Delay in inter-hospital transfer is a common reason for patients with acute ischemic stroke not receiving IA therapy, with estimated odds of treatment decreasing by 2.5% for every minute of transfer time.6 Evaluation of patients with acute stroke using ASPECTS is one of the key criteria recommended by the AHA when considering patients with acute stroke for endovascular interventions. Sun et al5 studied the rate of ASPECTS decay during inter-hospital transfer in patients treated with IA thrombectomy. The study showed that patients with good outcomes following thrombectomy had lower rates of absolute ASPECTS decay, with 1 unit increase in ASPECTS decline per hour corresponding to a 23-fold lower probability of a good outcome. All patients included in their analysis received endovascular therapies and the authors did not evaluate how many patients became ineligible for such treatment during inter-hospital transfer as a result of ASPECTS deterioration.
Our study examined an important question of how many patients who would have initially qualified for endovascular therapy based on favorable ASPECTS profile had progression of stroke towards unfavorable ASPECTS on repeat CT following inter-hospital transfer. Our analysis showed that one in three patients showed ASPECTS decay towards an unfavorable score (<6), and there were no reliable and simple criteria to identify which patients would show such evolution, except for NIHSS severity. Similar findings were reported in the study of the Madrid Stroke Network, in which analysis of the transfer of patients who ultimately do not undergo endovascular interventions was performed.7 The study reported no difference in baseline characteristics between the patients who were treated or excluded from IA interventions, and unfavorable neuroimaging criteria (defined as ASPECTS <7) were the reason for such ‘futile’ transport in 32% of those patients who ultimately did not undergo endovascular revascularization. However, because the main reason for exclusion from thrombectomy after the inter-hospital transfer was clinical improvement and spontaneous arterial recanalization (which occurred in 48% of patients who were ultimately excluded from thrombectomy), it is difficult to draw a conclusion from that study about the subgroup of patients whose imaging profile deteriorated during the transfer.
Our study was intended to analyze how ASPECTS decay during inter-hospital transfer might theoretically influence eligibility for IA thrombectomy rather than to study a correlation between ASPECTS and outcomes following thrombectomy, which has been dealt with elsewhere.3 ,4 ,8 At our institution, during the study period, the decision to proceed with thrombectomy was largely based on CT perfusion data rather than CT ASPECTS alone, as well as other clinical criteria, such as NIHSS severity, pre-stroke functional status, and life expectancy. In our cohort, a total of 18 patients underwent thrombectomy. Of those, five patients had poor ASPECTS, and none had a good clinical outcome. Two (15%) of the 13 patients with favorable ASPECTS showed good clinical outcome at 3 months (defined as modified Rankin scale of 0–2). Owing to the small sample size, no statistical analysis was performed on this subgroup of patients.
We speculate that patients who maintained favorable ASPECTS on repeat imaging might have had better intracranial collaterals, which are known to correlate with the extent and progression of stroke.9 ,10 However, lack of angiographic studies at the time of the initial imaging did not allow us to test that hypothesis. Time to repeat CT was, on average 57 min longer in patients with unfavorable ASPECTS. This difference, however, did not reach statistical significance, potentially owing to the overall small sample size, but might have led to evolution of higher ASPECTS in these patients. The average time from initial CT to repeat CT at our institution was 280 min (4.6 h), which indicates the need for significant improvement in the organization of intra-hospital transport. The study by Sun et al5 reported their median time between initial imaging to repeat imaging of 2.7 h. This time metric is different than a typically reported ‘transfer’ time because it also accounts for time spent interpreting the initial CT, clinical decision-making, and arrangements for the transfer to occur.
Inter-rater variability is a potential limitation of the CT ASPECTS grading system. Gupta et al,11 evaluated the interobserver reliability of ASPECTS for consecutive patients with anterior circulation ischemic strokes by grading the scans independently by two readers, and determining the effect of variability in rating on treatment decision-making. ASPECTS was the same for the two readers in only 34% of cases, and the difference in scores was as high as three points in some cases. The authors dichotomized ASPECTS ≤7 vs >7 for endovascular treatment selection, and estimated that approximately 25% of treatment decisions for IA therapy might be affected by inter-rater reliability.
Conclusion
Our study showed that during inter-hospital transfer, one out of three patients with stroke from anterior circulation LVO becomes ineligible for IA thrombectomy based on CT ASPECTS imaging criteria alone. Except for NIHSS severity, no other baseline clinical factors could identify which patients were at risk of ASPECTS deterioration. Our study indicates the critical importance of rapid transfer of all patients with stroke from suspected LVO to hospitals capable of carrying out endovascular treatment.
References
Footnotes
Contributors Conception and design: MM, RG, and WSB. Drafting the article, data acquisition, interpretation and analysis, and statistical analysis: MM and SS. Critical revision of the article: all authors. Study supervision: MM.
Competing interests None declared.
Ethics approval University of South Florida institutional review board.
Provenance and peer review Not commissioned; externally peer reviewed.