Ischemic Stroke Tissue-Window in the New Era of Endovascular Treatment.

Abstract

schemic stroke is a dynamic process of infarct expansion that varies as a function of time, residual blood flow, and other factors. Time can be measured easily but is an imprecise surrogate marker for brain physiology after stroke onset. After sudden intracranial artery occlusion, progression to brain infarction occurs quickly and on average, reperfusion therapies are not effective after several hours. 1–4 However, there is enough variance in the rate of infarct development that experienced stroke physicians can identify individual cases using brain imaging where reperfusion will be useful in later time windows after stroke onset. This imaging selective approach has proven effective in recent randomized controlled trials. Furthermore, the opposite situation also occurs, where the infarction is completed in a short time after stroke onset and reperfusion is futile despite early presentation to medical attention and rapid treatment. The use of time as a surrogate marker for brain physiology has historical precedent with a similar approach having been used in cardiology and in the trials of intravenous thrombolysis for stroke. Time's advantage is that it is easily and definitively measureable resulting in relative ease of widespread use for guidelines and performance measurement. Brain imaging has advanced and is the most readily available and valuable biomarker for stroke. We do not have additional tools akin to those available to our colleagues in Cardiology. The brain equivalents of the ECG and serum troponin levels have yet to be discovered. However, brain imaging in acute ischemic stroke has many advantages over serum markers because primary intracerebral hemorrhage can be readily identified and an estimation of the extent of the ischemic core and penumbra provided. Because the brain is immobile in real time, detailed noninvasive imaging of the brain parenchyma, neurovascular anatomy, and perfusion is possible and relatively easy to obtain. The recent endovascular treatment trials provide proof of efficacy of reperfusion. The principle of fast reperfusion is now firmly established. In each of these trials, eligibility criteria were deliberate and specific. This therapy only applies to an imaging-defined subset of patients with ischemic stroke; neuro-vascular imaging was the key physiological marker in each of these trials. In 3 of the 4 trials, a small ischemic core as identified by the Alberta Stroke Program Early CT Score (ASPECTS) on plain computed tomography (CT) or CT perfusion was required for inclusion after CT angiography (CTA) was used to demonstrate the presence of a large …

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