87 e-Letters

  • Early neurological improvement following mechanical thrombectomy with general anesthesia

    We read with interest the article by Soize et al. “Can early neurological improvement after mechanical thrombectomy be used as a surrogate for final stroke outcome?”[1] Based on their results, the authors concluded that early neurological improvement (ENI) 24 hours after thrombectomy is a straightforward surrogate of long-term outcome. However, all patients in this study were treated with conscious sedation (CS), and not general anesthesia (GA). The residual effects of GA may mask ENI and limit its utility as a surrogate for long-term outcome.[2]

    We performed a similar analysis of patients enrolled in a prospective single-center registry. The ability of ENI to predict 3-month functional independence was assessed by the area under the receiver operating characteristic curve (AUC) and compared using the independent-samples Hanley test. Multivariable linear regression assessing the relationship between anesthetic technique and ENI was also performed. The analysis received ethics approval.

    291 patients were treated with thrombectomy, with 261 (89.7%) procedures performed with GA, and 30 (10.3%) with CS. All patients were de-sedated and extubated more than 12 hours before 24-hour National Institutes of Health Stroke Scale assessment. 174 (59.8%) patients achieved 3-month functional independence. Baseline and procedural characteristics did not differ between GA and CS patients (all P>0.05). ENI demonstrated better prognostic ability in CS (AUC 0.91, 95% confiden...

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  • SPOT as a clinical decision aid

    We read with interest the response to our manuscript on using machine learning to optimize elderly patient selection for endovascular thrombectomy (1). We acknowledge here, as the author reports, the limitation of SPOT being based on single center data, and the need for multicenter prospective validation of SPOT as next step in development. The author raises additional technical concerns that we do not necessarily view as applicable to this study.

    First, we would like to stress the general limitations of artificial intelligence based techniques such as the overfitting and the data specific local optima problems. However, the specific comments brought by the author are not applicable in our case. First, studies on the number of events per predictor are applicable for logistic regressions (LRs) which is not used in the SPOT algorithm. In fact, our results show poor LR performance which is consistent with the rule of thumb of 1 to 10 referred to by the author. Hence, while serving as a good guidance for LR, the rule is not binding and more importantly it does not guarantee the generalization of the learned model. To further illustrate, classification models using convolutional neural networks have millions of parameters and are trained with datasets that, in most cases, do not have millions of samples in each group. However, these models have acceptable generalization capabilities and are tested using the data-split method. In SPOT, the model at its core is a regressi...

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  • Multiple Factors Related to Vessel Perforations in Endovascular Thrombectomy

    Congratulations to Annika Keuler et al¹ on their experience with the wireless microcatheter technique preventing vessel perforations in endovascular thrombectomy. Based on their results, the authors conclude that in most cases of mechanical recanalization, the clot can be passed more safely with a wireless microcatheter. In our daily work, we also find the wireless microcatheter technique seems to reduce subarachnoid hyperdensity resulting from vessel perforations. However it seems difficult to confirm this correlation; the details of which will be discussed as follows. After reading and analyzing the article carefully, we have some opinions about the study which we would like to communicate with the authors because the conclusions of the paper directly relate to our clinical experience.
    In the article, two radiological manifestations are defined as vessel perforations——contrast extravasation during angiography and angiographically occult ipsilateral circumscribed subarachnoid contrast extravasation which is identified by post-interventional CT scans. As confirmed by previous studies2-3, we agree with the authors on using immediate post-interventional CT examination to identify the subarachnoid hyperdensity due to intraoperative contrast extravasation. Based on their results, post-thrombectomy subarachnoid hyperdensity was observed on CT scans in 22 patients, in 18 of whom, the clot was passed using a microwire, and in the other four, using a wireless microcathete...

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  • Response to: "Using machine learning to optimize selection of elderly patients for endovascular thrombectomy"

    It is with great interest that we read the study of Alawieh et al(1), in which they developed a machine learning algorithm, called ‘SPOT’, to select stroke patients older than 80 years for endovascular therapy (EVT). Prediction modeling to optimize patient selection for EVT is an emerging topic of interest and we agree that predicting individual patient outcomes is increasingly important for decision making in medicine. However, we were surprised by the strong conclusions that were drawn by the authors, considering some serious limitations of the study.

    First, the size of the training set is insufficient to develop a complex model with twelve predictor variables and many correlations. Only 22 patients had a good functional outcome, which means that the number of events per tested predictor variable is less than two. For the development of a reliable model, a sample size of at least ten events per variable is needed to minimize the risk of overfitting(2, 3). It has been suggested that even far more events per variable are needed to achieve stable predictions with machine learning techniques(4). Especially complex models developed on small sample sizes have a high risk of overfitting, resulting in unstable predictions and too optimistic model performance measures. The reported AUC of 0.92 is therefore very likely to be an overestimation.

    Second, the SPOT algorithm provides a treatment advice based on the predicted outcome after treatment, without providing the...

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  • The AIS Denominator

    We had an opportunity to read the article by Lakomkin et al regarding systematic literature review of LVO prevalence. Since one of our studies is part of this review we feel compelled to comment on the paper. We do appreciate the authors’ efforts in conducting this analysis which is important in understanding the burden of disease – but, with respect offer some criticisms. The major limitation of the paper which the authors recognize is the heterogeneity of the included studies. Unfortunately, this limitation is so critical that it yields unreliable information at best and misleading at worst.

    The paper intends to study the prevalence of large vessel strokes. However, apart from a couple of population based studies in their review, the rest are a heterogenous mix describing an LVO rate from very selective cohorts of patients from single centers. Several are centered around validation of clinical scales for detecting LVOs. The key features of a population based study include a defined catchment population, access to a large part of that population and a reliable marker of disease. Without these a “prevalence” constitutes a report of a center’s experience of disease rate as it pertains to their patient intake. While still valuable it is not an estimation of the disease burden in the population that the center serves unless an overwhelming majority of that population comes to that center.

    The authors determine an average rate of about 30% LVO amongst acute isch...

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  • Reply to: Decreasing incidence of subarachnoid hemorrhage

    We would like to congratulate Nicholson et al. on their highly interesting work on the declining rate of SAH in the Irish population. This will certainly provide some very interesting points. Also in Germany there is - at least subjectively - the phenomenon of the declining rate of SAH. The authors can establish a clear correlation to the decline in the smoking rate. Now the question arises whether this is the only relevant correlation. In particular, it would certainly be necessary to investigate whether there has been an increased rate of detection of unruptered Aneurysma and an increasing rate of treatment of those during the study period and whether this may also have a relevant influence on the decrease in SAH.

  • Using an intermediate catheter triaxial system for Direct Aspiration first Pass Technique: the easiest way for thrombectomy?

    Dear Editor,
    we read with great interest the paper from Sallustio et al 1 regarding the use of new thromboaspiration catheter, AXS Catalyst 6 (Stryker Neurovascular, Mountain View, CA, USA), for endovascular treatment (EVT) of large vessel stroke (LVS) with A Direct Aspiration first Pass Technique (ADAPT)2.
    In our center, a team composed by 4 vascular interventional radiologists, two physicians with certified experience in stroke treatment and two physicians with large carotid stent experience, and 4 stroke neurologist with large experience in intravenous thrombolysis, started to perform EVT in patients with LVS of anterior or posterior circulation from September 2017.
    Given the wide availability of different systems of neurothrombectomy we decided to use AXS Catalyst 6 both for its technical features, as reported by Sallustio et al, both for its lower costs than the others available (6F SOFIA plus catheter, MicroVention, Tustin, CA, USA; the X Penumbra ACE catheters, Penumbra Inc., Alameda, CA, USA).
    Between September 2017 and May 2018, 24 patients (72.1 ± 13.2 years old) affected by acute ischemic stroke with LVS underwent to EVT in our center. Median baseline NIHSS was 18 (range: 7-24). Intravenous thrombolysis was used in 5 patients.
    The most frequent site of occlusion was the middle cerebral artery (MCA) (70.8%), while in 16.7% of cases was basilar artery. Tandem occlusions occurred in 12.5% of patients and the most frequent stroke etiolo...

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  • Repeatability when measuring porosity and pore density of flow diverters: can we measure in vivo?

    The paper by Farzin et al.[1] shows interesting results about measuring porosity of fully expanded flow diverter stents using (photographic) images of the stent being assessed. In their study, authors used 3 different methods and repeated measurements by different observers to assess the porosity of stents. According to their results, the variability when measuring porosity is so large that previous works assessing it should be questioned. On the other hand, they indicate that pore density seems to be more reliable and repeatable. The study highlights the difficulty of measuring such parameter in a controlled in vitro environment. After carefully reading the article, it became clear that the most reproducible way of measuring porosity, from the 3 options studied, was M3 (based on measuring the width and length of the struts and number of struts per reference square). Furthermore, some simple assumptions should improve the results and substantially reduce errors and variability:
    1. Wire width: the value for wire width, indicated by the manufacturer, is likely to be more accurate. If this value is no to be trusted, at least in average, then the reproducibility of the manufacturing process could not be trusted. Measuring wire width directly on the images is likely to introduce error as it might be affected by reflection/refraction of light on the wire material and wire coating, as well as lens imperfections or optical aberrations in some cases.
    2. Calculating poro...

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  • Response to “Impact of balloon guiding catheter on technical and clinical outcomes: a systematic review and meta-analysis”

    I read with great interest the meta-analysis by Brinjikji et al.1 which evaluated outcomes after mechanical thrombectomy for acute ischemic stroke by using a balloon guiding catheter (BGC) device. In that study, the authors documented that patients who underwent mechanical thrombectomy with BGC had better clinical and angiographic outcomes than those without BGC. However, there were some issues which should be addressed and discussed.
    First, the number of successful recanalizations, shown as 2b/3 of Thrombolysis In Cerebral Infarction (TICI) grade in Fig.3 in the article,1 might be not accurately described. The events of successful recanalization were noted in 113 of 149 in the BGC group and 133 of 189 in the non-BGC group according to Nguyen et al.2 However, the events were presented as 112 of 149 in the BGC group and 135 of 189 in the non-BGC group.1 Accordingly, the forest plot can be changed as in Fig. 1 below. Mechanical thrombectomy using BGC exhibited significantly higher successful recanalizations than did non-BGC use (OR, 1.710; 95% CI: 1.099-2.662). Second, there was no specific explanation for the publication bias of Fig. 4 in the result section.1 Although the authors reported a p value of 0.49 using Egger’s regression, we are not sure what publication bias meant to represent, successful recanalization or clinical outcome or other variables.
    In this letter, we made a funnel plot for successful recanalization based on the revised number of events we h...

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  • Reduction of ghost infarct core with TMax/CBF mismatch in CT perfusion

    TO THE EDITOR: We read with interest the recent paper by Boned and colleagues.1 The authors conclude that “CT perfusion may overestimate final infarct core, especially in the early time window. Selecting patients for reperfusion therapies based on the CTP mismatch concept may deny treatment to patients who might still benefit from reperfusion”. We completely agree with this consideration, mainly when, as in this article, the core volume is assessed according to the classical CT perfusion (CTP) mismatch mean transit time (MTT)/cerebral blood volume (CBV)2 by measuring the lesion on CBV maps generated with a one-phase CT perfusion (CTP) acquisition protocol. In fact, it is well-known that a short CTP scan duration often produces a truncation of the perfusion curves resulting in an overestimation of CBV lesion that can frequently reverse.3 In addition, it has recently been demonstrated that relative cerebral blood flow (CBF) < 30% and time to peak of the residual function (Tmax) > 6 seconds is more reliable than CBV < 2.0 ml/100gr and relative MTT > 145% in identifying infarct core and ischemic penumbra at admission, respectively.4,5 As a consequence, the new CTP mismatch model Tmax/CBF was successfully used to include acute ischemic stroke (AIS) patients in the last trials showing the efficacy of endovascular treatment.6-9 We recently treated with combined intravenous thrombolysis and with mechanical thrombectomy patients imaged within 1.5 hour from symptom onset...

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