Emergency Medicine is Hard

Overview

• Approximately 80% of strokes are ischemic and 20% are hemorrhagic
• Ischemic strokes
  • Cardioembolic (e.g. cardiac emboli from atrial fibrillation or valvular disease) or atherothromboembolic
  •  Lacunar ischemic stroke is a subset of ischemic stroke thought to be owing to intrinsic disease of a single perforating cerebral arteriole (“small vessel disease”) that affects only a small volume of subcortical tissue and causes distinct clinical syndromes.
  • Ischemic strokes are complicated by secondary hemorrhagic transformation
• Hemorrhagic strokes
  • Arise due to an underlying vascular abnormality such as aneurysm, amyloid angiopathy, small-vessel disease, venous sinus thrombosis, or anticoagulation
  • Hypertension is the major risk factor

Treatment of Stroke

• Ischemic strokes
  • Intravenous thrombolytics (tPA, TNK)
    • The effectiveness of thrombolytic therapy declines with time and has the greatest benefit if treatment begins within the first 3 hours from symptom onset
    • SITS data show comparable rates of hemorrhage, death and good outcome among stroke patients treated with intravenous rt-PA within the first 3 h (n = 25,279) and those treated between 3.0 and 4.5 h (n = 4056); even those treated “off-licence”, that is, between 4.5 and 6.0 h from stroke onset (n = 283) did not show a significant increase in the rates of poor outcome
      • Note: Data in the US recommends a cut-off of 4.5 hours
  • Aspirin
    •  Two very large randomized controlled trials found in a total of nearly 40,000 acute ischemic stroke patients that those randomized to receive daily aspirin suffered fewer (10 per 1000) recurrent strokes and fewer deaths in the first 6 months after stroke
  • Endovascular retrieval of intra-arterial clot (mechanical embolectomy) or direct intra-arterial delivery of thrombolysis
    • Thrombolytics with endovascular therapy had no added benefit
• Hemorrhagic stroke
  • The treatment for hemorrhagic stroke is currently primarily supportive unless there is a specific underlying cause such as aneurysm.

Evidence for imaging practices in stroke

• Non-contrast head CT
  • Primary imaging modality in the initial assessment of acute stroke
  • Assists in excluding hemorrhage and non-vascular causes
  • Can identify early ischemic changes in patients with moderate to severe strokes
  •  A recent multicenter review of the imaging received by >12,000 stroke patients in the USA prior to administration of intravenous thrombolysis, showed that over a 4-year period, the number of patients being imaged with non-contrast CT alone dropped from 64% to 55%

• MRI
  • MRI in stroke requires at least four sequences, namely T₂ weighted, diffusion-weighted imaging (DWI), T₂ and fluid-attenuated inversion recovery (FLAIR in order to identify hemorrhage, ischemia, underlying structural changes (mimics) and factors such as leukoaraiosis
  • Most appropriately used in mild strokes since this process takes about 15 minutes of in-scanner time
  • The main advantage of MRI in acute stroke relates specifically to the use of DWI, which can provide very clear evidence of the extent of parenchymal ischemia and/or infarction within minutes of stroke onset and can do so more sensitively than non-contrast CT within the first 6 h from the onset

• Angiography (CTA/MRA)
  • Angiography in acute stroke aims to provide the location and extent of any potentially treatable thrombus or embolus
  • Standard CTA and MRA only allow interpretation of luminal narrowing or focal occlusion 
  • The expectation is that angiography could improve intravenous thrombolysis treatment decision-making by focusing treatment on patients with a blocked artery, thus avoiding exposing patients without a blocked artery to the risk of rt-PA.

• Perfusion imaging
  • Aims to provide an accurate and understandable depiction of the non-salvageable infarct extent (core of dead tissue) and to contrast this with the volume of potentially salvageable tissue that is ischemic and at risk but has not yet infarcted (penumbra). 
  • The concern is that infarcted tissue is more likely than ischemic tissue to undergo reperfusion injury and subsequent hemorrhage following restoration of blood flow. Perfusion imaging has been used to predict which patients are more likely to suffer from hemorrhagic transformation of infarct following thrombolysis
  • One of the major difficulties faced by researchers in this area is the plethora of perfusion parameters and thresholds that have been suggested as differentiating core from penumbra and the large variability in the current definitions of core and penumbra.

Sources:

• https://pmc.ncbi.nlm.nih.gov/articles/PMC4112390/#s5