Publications by authors named "Gregory B Walker"

4 Publications

  • Page 1 of 1

Is This Contrast? Is This Blood? An Agreement Study on Post-thrombectomy Computed Tomography Scans.

Front Neurol 2020 22;11:593098. Epub 2020 Dec 22.

Ottawa Stroke Program, Department of Medicine (Neurology), University of Ottawa, Ottawa, ON, Canada.

Hemorrhagic transformation after acute ischemic stroke is a dreaded and severe complication of thrombolysis and thrombectomy. However, its detection on post-thrombectomy conventional non-contrast computed tomography (CT) scan can be complicated by the frequent (and sometimes concomitant) presence of contrast, resulting in changes in management. Our objective was to assess the inter- and intra-rater reliability for the detection of blood and/or contrast on day-1 post-thrombectomy CT scans. A total of 18 raters across 3 different specialties independently examined 30 post-thrombectomy CT scans selected from the Aspiration vs. STEnt-Retriever (ASTER) trial. They were asked to judge the presence of blood and contrast. Thirty days later, the same 18 raters again independently judged the 30 scans, in randomized order. Agreement was measured with Fleiss' and Cohen's statistics. Overall agreement on blood and/ or contrast presence was only fair, = 0.291 (95% CI = 0.273-0.309). There were 0 scans with consensus among the 18 readers on the presence of blood and/or contrast. However, intra-rater global agreement across all 18 physicians was relatively high, with a median kappa value of 0.675. This intra-rater consistency was seen across all specialties, regardless of level of training. Physician judgment for the presence of blood and/or contrast on day-1 post-thrombectomy non-contrast CT scan shows limited inter-observer reliability. Advanced imaging modalities may then be warranted for challenging clinical cases.
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December 2020

Dual origin of the right vertebral artery from the right common carotid and aberrant right subclavian arteries.

J Clin Neurosci 2018 Jul 30;53:258-260. Epub 2018 Apr 30.

Department of Neurology, University of Pittsburgh Medical Center, Pittsburgh, USA; Department of Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, USA. Electronic address:

This report describes a case of duplicated origin of the right vertebral artery incidentally found in a young patient. Computed tomographic angiography and digital subtraction angiography showed a dominant branch derived from the right common carotid artery and an accessory branch that derived from the right subclavian artery, which aberrantly originated from the far left aortic arch, and adjoined the dominant branch at the C5 level. We discuss angiographic findings, clinical implications and embryological basis for this rare anomaly.
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July 2018

Assessing the efficacy of endovascular therapy in stroke treatments: updates from the new generation of trials.

Expert Rev Cardiovasc Ther 2017 Oct 4;15(10):757-766. Epub 2017 Sep 4.

a University of Pittsburgh Medical Center , Pittsburgh , PA , USA.

Introduction: For the past 20 years, intravenous recombinant tissue plasminogen activator (rt-PA) has been the only proven treatment for acute ischemic stroke. Large arteries such as the internal carotid artery, the middle cerebral artery and the basilar artery supply blood to large volumes of brain tissue. When occluded, these vessels may have low response rates to rt-PA resulting in devastating injury and death. Areas covered: In 2013, three trials evaluating the efficacy of mechanical thrombectomy in acute stroke were neutral, however, lessons learned from these trials resulted in a second generation of five trials in 2015 and a sixth in 2016 which all demonstrated significant benefit for select patients. Here we will review the evidence behind these new trials and. introduce new questions such as models of care, techniques of thrombectomy, the role of rt-PA, modes of anesthesia, the management of late presenting and wake up strokes among other real world challenges facing stroke medicine now that the thrombectomy is an evidence based treamtnent Expert commentary: The mechanical thrombectomy is now the new standard of care and with that comes the need to find ways to provide it to all who will benefit.
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October 2017

Altered cytokine profiles of human retinal pigment epithelium: oxidant injury and replicative senescence.

Mol Vis 2013 21;19:718-28. Epub 2013 Mar 21.

Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, British Columbia, Canada.

Purpose: Age-related macular degeneration (AMD) is a local, chronic inflammatory disease of the eye that is influenced by oxidative stress and dysregulation of the retinal pigment epithelium (RPE) associated with aging. The purpose of this study is to characterize the effects of oxidative stress and replicative senescence on the secreted cytokine profiles of RPE in vitro.

Methods: We used multiple, serial passages of human RPE cells from primary culture as an in vitro model of aging. Responses of early passage 5 (P5) and late passage 21 (P21) RPE cells were compared. Oxidative stress was induced in RPE cells (P5) by exposure to 75 μM hydroquinone (HQ) for 24 h. The secretome profiles of the RPE cells were measured with a multiplex suspension assay that assayed human cytokine, chemokine, and growth factors. Immunohistochemistry on younger (≤55 years old) and older (≥70 years old) human post-mortem donor eyes was used to verify selected cytokines.

Results: Supernatant of HQ-treated RPE cultures exhibited increased secreted levels of vascular endothelial growth factor (VEGF), interleukin (IL)-12, and IL-10 that reached statistical significance (p<0.05). Supernatant of late passage P21 RPE cultures exhibited decreased secreted levels of stromal cell-derived factor (SDF)-1α, granulocyte macrophage colony-stimulating factor (GM-CSF), IL-8, IL-15, IL-6, and an increased level of IL-1ra compared to early passage P5 RPE cultures that reached statistical significance (p<0.05). Immunohistochemical analysis demonstrated increased expression of IL-1ra in RPE cells from older post-mortem donor eyes (≥70 years old) versus younger eyes (≤55 years old).

Conclusions: Our data demonstrate a unique cytokine secretion profile of primary culture RPE cells at early and late passage. Our in vitro data suggest an age-specific modulation of cytokine secretion in RPE and is consistent with immunohistochemical analysis on post-mortem eyes. The secretion profile associated with RPE under conditions that mimic oxidative stress, another factor associated with the pathogenesis of AMD, emphasizes upregulation of the angiogenic growth factor, vascular endothelial growth factor. Together, these data support the role of advanced age and oxidative stress in inflammatory cytokine modulation in RPE cells.
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September 2013