Revisiting Current Golden Rules in Managing Acute Ischemic Stroke

Background on rCBF

  • Neurologic deficits occur when relative cerebral blood flow falls below ischemic threshold (22 mL per 100 g per minute).
  • The infarct threshold is 10 mL/100 g/minute. Ischemic penumbra is the target tissue for prompt reperfusion therapy because it is impaired but above the infarct threshold (10 to 22).
  • Untreated penumbra quickly converts into infarction.

Golden Rule Discussion (Refutation)

  1. Imaging-based hypoperfusion indicates ischemia.
    1. Hypoperfusion of parenchyma does not necessarily indicate tissue at risk.
    2. This is a reflection of lower relative cerebral blood flow and can be due to any number of causes.
    3. In essence, hypoperfused tissue lies in the spectrum of ischemia, penumbra and infarct.
  2. Mean transit time abnormality indicates tissue at risk.
    1. The spectrum of terms of ischemia, penumbra, oligemia and infarct should not be used interchangeably because oligemia tissue is not necessarily at risk for infarct (chronically hypoperfused tissue).
    2. Specifically, chronic proximal arterial occlusion is commonly seen and could result in a decreased mean transit time without risking tissue.
    3. In fact, chronically hypoperfused “starving” parenchyma may tolerate lower cerebral blood flow more than normal parenchyma.
  3. Diffusion weighted imaging of normality indicates infarction.
    1. This is not necessarily true because there can be spontaneous resolution of hypoperfusion. There are cases of oligemia that recover without treatment.
  4. Perfusion weighted imaging/diffusion weighted imaging mismatch indicates ischemic penumbra.
    1. Mean transit time-diffusion weighted imaging mismatch includes only ischemia, penumbra and infarction core.
  5. There is a fixed therapeutic window.
    1. The concept of therapeutic window has a lot of variance.
    2. The window for treatment should be individualized to the patient and depends on relative cerebral blood flow.
    3. Contralateral rCBF should be considered in evaluation.
  6. “Time is brain”.
    1. The article specifically states that inappropriate revascularization of the infarct core can convert the golden rule “time is brain into “time is blood”.

Source

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