eLetters

74 e-Letters

  • Response to Rouchaud

    We thank the respondents for providing their case experience and allowing further discussion of this important topic. We would first like to draw attention to specific points in the described case, before discussing some of the more general issues raised.

    The respondents report one of many scenarios in which it may be undesirable to use dual antiplatelet therapy in the elective treatment of intracranial aneurysms with flow diverters. In this case, a 47-year-old woman with an 11 mm left ophthalmic aneurysm harbours a significant aspirin allergy. A single Pipeline Shield device under cover of ticagrelor was used to treat the aneurysm. The patient was well at discharge on postoperative day three but then developed symptomatic stent thrombosis on day 6. We draw attention to three points:

    1) The respondents state that the stent achieved “perfect wall apposition improved with intra-stent balloon angioplasty.” Setting aside the impossibility of improving “perfect wall apposition” with angioplasty, this does allude to the increasingly understood importance of flow diverter wall apposition. [1] However, digital subtraction angiography assess stent apposition poorly. [1] The use of angioplasty suggests that there may have been some initial concern. Moreover, angioplasty itself may contribute to thrombosis if it promotes activation of the extrinsic clotting pathway by disrupting the endothelial layer. The phosphocholine “Shield” layer reduces thrombosis and platelet...

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  • Alert against the risk of single antiplatelet therapy while using Pipeline Shield flow diverter

    We read with interest the case series by Manning’s et al.[1] using a surface modified flow-diverter stent (Pipeline Flex with Shield Technology, Medtronic Neurovascular, Irvine, California, USA). In this retrospective series, 14 ruptured intracranial aneurysms have been treated in the acute phase after Sub-Arachnoid Hemorrhage (SAH) with the Pipeline shield device under a Single Anti-Platelet Therapy (SAPT). The article concluded the PED-Shield to be safe to use in the acute treatment of ruptured intracranial aneurysms with SAPT.

    However, in this small series, the authors reported one case of total stent occlusion and two cases of platelet aggregation noted on the PED-Shield device requiring to switch from single to dual antiplatelet treatment. Considering those three patients, thrombotic complications have been observed in 21.4 % of cases (3/14) in the acute period. Furthermore, in two cases (14.3 %), the authors reported rebleeding of the culprit aneurysm leading to patient death, pointing out the fact that flow-diverter devices may not immediately prevent the risk of aneurysm rerupture.

    Anti-thrombogenic coating might have an added value in case of very specific aneurysms cases requiring the placement of a stent in the acute phase after rupture. Those specific cases are mainly dissecting or blister aneurysms for which endovascular or even surgical approach are difficult and carry a high risk of morbi-mortality[2][3]. In case of endovascular treatment, rece...

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  • Proprietary nature of intravascular medical device coatings limits safety testing

    Proprietary nature of intravascular medical device coatings limits safety testing

    Dear Dr. Albuquerque:

    We are glad that our work has generated interest and discussion in the field [1]. Four years have elapsed since a need for updated device coating testing was officially announced [2], however complexities on the matter and persistent knowledge gaps limit safety studies of devices currently on the market for clinical intravascular use [3,4]. Standardized in vitro particulate generation testing is needed. However, available literature shows that preclinical device testing is not fully predictive of clinical response. Therefore, in vitro and animal studies cannot replace investigation in humans. Currently, lack of consensus on the following prevent meaningful testing in humans: I) optimal clinical testing methods; ii) definitions of permissible risk; iii) adverse cellular, organ, and temporal-specific effects of distinct coating biomaterials; and iv) effects of pre-existing comorbid conditions. Nevertheless, in vitro testing that does not incorporate clinical data has limited utility for safety guidance. Likewise, in vivo studies that do not incorporate biomaterial factors are incomplete. Thus, the proprietary nature of intravascular device coatings remains a significant limitation to clinical device testing and safety assurances. Growing data [2-6] suggest that it may be time for this to be addressed.

    1. Chopra AM, Hu YC, Cruz JP. The Device Specific...

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  • The Device Specific Nature of Polymer Coating Emboli: An Optimal Approach For Future Investigations Related to Polymer Embolism

    An increasing number of reports highlight polymer coating embolism as an iatrogenic complication of intravascular medical devices [1-3]. Autopsies, histologic evaluations of thrombectomy specimens, samples of captured debris, resected or biopsied tissues, are available methods used to study polymer emboli post investigative catherizations or interventional procedures. Reported data highlight the prevalence of this phenomenon and/or its clinicopathologic impacts, however, fall short of identifying higher-risk polymer emboli interventional devices. Consequently, an optimal approach for future investigations related to polymer coating embolism is required.

    Mehta et. al investigate the histologic frequency of polymer emboli among patients who underwent endovascular thrombectomy for treatment of acute ischemic stroke due to large vessel occlusion by retrospectively evaluating thrombectomy specimens [2]. In this study, the reported frequency of polymer emboli includes the use of various devices and techniques among selected cases. However, literature highlights polymer coating embolism is device specific and dependent on coating integrity measured by particulates released [4]. Thus, the use of alternate devices with higher or lower particulate release for a given procedure may result in a large variation in incidence rates from reported results. Also, as mentioned by the authors, subsequent statistical correlations unless appropriately powered provide limited informatio...

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  • Reply

    Dear Editor,
    We would like the thank Drs. Berndt, Zimmer, Kaesmacher, and Boeckh-Behrens for their interest in our study titled “Clot permeability and histopathology: Is a clot’s perviousness on CT imaging correlated with its histologic composition?” We read their letter with interest. The authors have been pioneers in stroke clot analysis and we greatly respect their academic rigor and expertise.

    While we agree that there are certainly some methodological differences between our two studies, we do not believe that these are to blame for the differences in results. Rather, we feel that the observed differences in results between our studies could be due to differences in our patient populations.

    Our group has previously shown that there is indeed a correlation between clot composition and etiology. In a recently published article in Stroke we found that large artery atherosclerosis clots were more likely to be platelet rich than those of a cardioembolic origin.1 To date, however, we have yet to find any definite correlation between etiology and RBC density or fibrin density, and we think it is too early to make any definite conclusions on the association between clot composition and etiology.

    We agree that the association between perviousness, clot composition, etiology and clinical outcome is not conclusively clarified yet, and hence warrants further research, especially in a larger patient group in a multi-centric setting. Currently, our gr...

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  • Letter by Berndt et al. Regarding Article “Clot permeability and histopathology: is a clot’s perviousness on CT imaging correlated with its histologic composition?”

    Recently, we have read with great interest the article by Benson et al. “Clot permeability and histopathology: is a clot’s perviousness on CT imaging correlated with its histologic composition?” [1].
    It is pleasing, that research in the field of thrombus characterization by perviousness and its association to thrombus composition is emerging. Benson et al. report a higher clot perviousness for RBC rich clots in comparison to fibrin dominant thrombi [1]. These results stand in contrast to our previously published study [2], that shows an association between perviousness and fibrin rich clots. We furthermore validated those findings in a large collective by showing a relationship between perviousness and cardioembolic origin. Further research to this special topic is scarce. However, there is another experimental and therefore well controllable study on artificial clots, that showed a strong association of fibrin content and contrast agent uptake [3], similar as it has been shown for in vivo thrombi in our study [2].
    Consequently, these contradictory results demand further explanations. In our opinion, the differing results might be caused by methodological differences, which we want to discuss.
    First, thrombus localizations should be taken into account. Benson et al. used a collective of 57 thrombi with different thrombus locations (38 MCA, 6 ICA, 5 ICA/MCA, 3 basilar artery, 2 posterior cerebral artery, 2 ICA/MCA/ACA, 1 ICC/MCA). It is at least questiona...

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  • Contraindicated micro catheters

    The authors describe two endovascular techniques for delivering IA chemotherapy to retinoblastoma patients. Technique A where a 1.2 Fr or 1.5 Fr micro catheter with continuous verapamil flush is advanced without a guide and technique B where a1.5 Fr or 1.7 Fr micro catheter is advanced within a 4 Fr catheter, through a 4 Fr sheath. We usually use a no sheath technique, using a 4Fr diagnostic catheter as a guide catheter for neonatal and pediatric cases. Most importantly, we do not use Echelon or Marathon micro catheters in neonatal and pediatric patients because their use is contraindicated per "instructions for use".

  • 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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