Definitions

Definitions

Acute stroke: An episode of symptomatic neurological dysfunction caused by focal brain, retinal or spinal cord ischemia or hemorrhage with evidence of acute infarction or hemorrhage on imaging (MR, CT, retinal photomicrographs), and regardless of symptomatic duration.

Ischemic stroke: An episode of neurological dysfunction caused by focal cerebral, spinal, or retinal cell death attributable to ischemia (blockage of an artery or vein), based on pathological, imaging, or other objective (clinical) evidence of cerebral, spinal cord, or retinal focal ischemic injury or until other etiologies have been excluded. Traditional definitions suggested that symptoms of stroke must last > 24 hours, but time-based definitions are now often reconsidered based on more advanced neuroimaging. 

Transient ischemic attack (TIA, sometimes referred to as a “mini-stroke”): A clinical diagnosis that refers to a brief episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia, with clinical symptoms, and without imaging evidence of infarction (Easton, 2009; Sacco et al., 2013). TIA and minor acute ischemic stroke fall along a continuum. TIA symptoms fully resolve within 24 hours and usually within one hour. If any symptoms persist beyond 24 hours, this is considered a stroke, although this continuum cannot be differentiated by symptom duration alone. A TIA is significant as it can be a warning of a future stroke event. Patients and healthcare professionals should respond to an acute TIA as a medical emergency. 

Minor non-disabling ischemic stroke (sometimes referred to as mild or non-disabling stroke): A brain, spinal, or retinal infarct that is typically small and associated with a mild severity of clinical deficits or disability. It may not require hospitalization.  Practically speaking, deficits that if unchanged, would not impair the patient’s ability to perform their ADLS, work and/or walk independently (based on PRISMS trial, 2018).

Note: For practical purposes, assessment, diagnosis, and management of individuals presenting with symptoms of TIA or minor ischemic stroke should follow similar processes as those throughout this module. Differentiating between TIA and minor stroke is less relevant and condition management should be informed by clinical history, presentation, and diagnostic imaging. Evidence shows that at least 20% of individuals presenting with TIA will experience a subsequent and more involved stroke, highlighting the need for aggressive secondary prevention for this group (OSVASC, NEJM, 2016).

Cerebral venous thrombosis (CVT): Thrombosis of the veins in the brain, either the dural venous sinuses or the more upstream cortical or deep veins. CVT may be present with neurological deficits due to venous congestion (sometimes called venous infarction) or due to hemorrhage. In the mildest circumstance CVT will present with headache only and sometimes with retinal edema (papilledema) and associated visual changes. CVT is an uncommon cerebrovascular disorder, accounting for <1% of all stroke syndromes.

Cryptogenic stroke: Cryptogenic stroke is defined as a brain infarction not clearly attributable to a definite cardioembolism, large artery atherosclerosis, small artery disease, or other identifiable cause despite extensive investigation (Saver et al., 2017). This group accounts for 25 to 40% of all strokes (Saver, 2016; Yaghi et al., 2017).

Embolic stroke of undetermined source (ESUS): A subset of cryptogenic strokes that represent approximately 9 to 25% of ischemic strokes, that meet the following criteria (Tsivgoulis et al., 2019; Ntaios, JACC 2020):

• Acute brain infarct visualized on neuroimaging; not a subcortical lacune <1.5 cm.
• Absence of proximal atherosclerotic arterial stenosis >50%
• No atrial fibrillation or other major-risk cardioembolic source
• No other likely cause of stroke (e.g., dissection, arteritis, cancer)

Mobile stroke unit: A mobile stroke unit has both the medical expertise and imaging technology to evaluate and treat patients with suspected stroke rapidly and accurately. The most important benefit of the mobile stroke unit is rapid diagnosis of the stroke type, allowing hemorrhage to be ruled out and treatment with intravenous thrombolysis to be started quickly if appropriate. Generally, these patients are referred to a hospital with CT imaging and a stroke (or telestroke) program (Shuaib & Jeerakathil, CMAJ, 2016).

Timeframes:

• Prehospital and emergency department stroke care: The key interventions needed for the assessment, diagnosis, stabilization, and treatment in the first hours after stroke onset. This includes all prehospital and initial emergency care for TIA, ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and acute cerebral venous thrombosis. This stage involves rapid triaging of patients based on time of symptom onset, stroke acuity, and brain imaging. Treatments may include acute intravenous thrombolysis or acute endovascular interventions for ischemic stroke, emergency neurosurgical procedures, and same-day TIA diagnostic and risk stratification evaluation. 
  
  The principal aim of this phase of care is to diagnose the stroke type, and to coordinate and execute an individualized treatment plan as quickly as possible.
  
  Prehospital and emergency department care is time-sensitive by nature: minutes for disabling stroke and hours for TIA. In addition, specific interventions are associated with their own individual treatment windows. Generally, this ''hyperacute" time-sensitive window refers to care offered in the first 24 hours after an acute stroke (ischemic and hemorrhagic) or TIA. 

• Acute stroke care: The key interventions involved in the assessment, treatment or management, and early recovery in the first days to weeks after stroke onset. This encompasses all of the initial diagnostic procedures undertaken to identify the nature and mechanism of the stroke, interdisciplinary care to prevent complications and promote early recovery, institution of an individualized secondary prevention plan, and engagement with the person with stroke and their family to assess and plan for transition to the next level of care, which includes a comprehensive assessment of the person’s rehabilitation needs. New models of acute ambulatory care such as rapid assessment TIA and minor stroke clinics or day-units are also starting to emerge.
  
  The principal aims of this phase of care are to identify the nature and mechanism of stroke, prevent further stroke complications, promote early recovery, and, in the case of the most severe strokes, provide palliation and end-of-life care.
  
  Generally, "acute care" refers to the first days to weeks of inpatient treatment. The person with stroke then transitions from acute care to inpatient or community-based rehabilitation; home, with or without support services; continuing care; or palliative care. This acute phase of care is usually considered to have ended either at the time of discharge from the acute stroke unit or 30 days after hospital admission.

Hemorrhagic stroke: A stroke caused by the rupture of a blood vessel within the brain tissue, subarachnoid space or intraventricular space.

Intracranial hemorrhage includes bleeding within the cranial vault and encompasses intraventricular, intraparenchymal, subarachnoid, subdural and epidural hemorrhage.

Spontaneous, nontraumatic intracerebral hemorrhage is bleeding within the brain parenchyma without obvious systemic, neoplastic, traumatic, or macrovascular etiology. This stroke subtype accounts for about 10-15% of all strokes and a disproportionately higher number of stroke related deaths. ICH are often categorized according to their location within the brain: lobar, deep, cerebellar, and brainstem.

Hemorrhagic infarct: Hemorrhagic infarct is defined as a hemorrhagic transformation into an area of arterial ischemic infarction or venous thrombosis associated tissue congestion.

Criteria for Stroke Centres Providing Acute Ischemic Stroke Treatment

Within the Canadian Stroke Best Practices Optimal Acute Stroke Services Framework, all hospitals in Canada have been assessed based on their capacity to provide guideline-directed stroke care. Each acute care hospital in Canada has been classified as belonging to one of five stroke service levels (refer to Figure 2). 

• Level 1 and 2 hospitals do not provide emergent acute stroke services. Level 3, 4, and 5 hospitals have increasing levels of coordinated stroke care services, including on-site CT imaging and acute thrombolysis. 
• Level 3 hospitals are primary stroke centres that provide intravenous thrombolysis, with or without virtual telestroke support, but they do not have acute stroke units. 
• Level 4 hospitals are primary or district or advanced stroke centres that offer on-site intravenous thrombolysis and have acute inpatient stroke units. Neurosurgical services are available at some Level 4 centres. 
• Level 5 hospitals are comprehensive stroke centres that provide advanced stroke care including endovascular interventions, and neurosurgical and advanced interventional radiology services.

Level 4 and 5 centres accept transfers from less resourced centres to provide advanced treatment and access to rehabilitation. 

Level 5 comprehensive stroke centres must meet the following criteria to provide endovascular thrombectomy (EVT):

1. A designated stroke team that includes physicians with stroke expertise (e.g., stroke neurologist or other physicians with advanced stroke training); stroke nurses and advanced practice nurses and/or nurse practitioners; neurosurgeons; (neuro)-radiologists, emergency physicians; critical care physicians; rehabilitation therapists (i.e., physical therapists, occupational therapists, speech-language pathologists), dieticians, pharmacists, and social workers.
2. On-site neurointerventional expertise with 24-hour access, seven days a week. 
3. On-site neurosurgery support and neurocritical care services. 
4. On-site stroke imaging with 24-hour access to a scanner and rapid interpretation of images, seven days a week, including a computed tomography (CT) scanner (i.e., third-generation or higher helical scanner) with programming for CT angiography (CTA). Multiphase or dynamic CTA or CT perfusion (CTP) imaging can also be used if available on-site. Magnetic resonance imaging, angiography, or perfusion (MRI, MRA, MRP) may be considered if available on site and will not delay acute stroke treatments.
5. Capability to administer intravenous thrombolysis.
6. On-site designated acute or comprehensive stroke unit, which is a specialized, geographically defined hospital unit dedicated to the management of patients with stroke, staffed by an experienced interdisciplinary stroke team, and providing a complex package of evidence-based care (e.g., protocols, care pathways) for acute stroke management, early rehabilitation, and education to people with stroke in hospital.