Stroke

What is a stroke

A stroke is when your brain is starved of blood flow, through blood not flowing (due to blockage of lack of supply), which is an ischaemic stroke, or through blood escaping from vessels and not enough entering the areas where it is needed, a haemorrhagic stroke.

These are life threatening events and kill 2500 people in NZ every year, the 3rd largest killer. 90% of deaths occur over 65.

Types of stroke

The types of stroke are the 2 previously mentioned, Ischaemic and haemorrhagic, and there are subsets under each of these.

Ischaemic stroke

Ischaemic is when there is a blockage of blood supply to the brain in the vessels, and can be global or focal. Focal cerebral ischaemia can be caused by an embolus or thrombus in a vessel.

Global ischaemia is from severe hypoxia/hypotension

Global cerebral ischaemia

In GCI we have shock or hypoxia leading to ischaemia in the brain, which should resolve on increasing BP or blood oxygen. However damage in the infarcted regions might still remain. The pattern of infarction tracks with “watershed” areas, which are most distal to the supplying arteries, and have shared supply. These regions are the ACA-MCA watershed and MCA-PCA watershed (see picture)

Focal ischaemia

Focal ischaemia is where you have a localised blockage, which is either thrombotic or embolic which occludes a vessel. the vessels can be large (MCA) or small (as in the brainstem). The symptoms depend on where in the brain the occlusion is and can either persist indefinitely or dissipate (a Transient Ischaemic Attack).

The sources of thromboemboli is mainly the heart, from valvular disease, atrial fibrillation, and MI, or from the carotid arteries and aorta, where thrombi can form over atherosclerotic plaques. These can travel with the blood until they block a vessel. Additionally paradoxical emboli from venous thrombosis can cause stroke, if a patient has a cardiac septal defect (like patent foramen ovale).

Also other emboli can cause occlusion, like air, fat, septic matter, and amniotic fluid.

Thrombosis can also lead to stroke, due to clotting in the cerebral vessels, due to plaque rupture or etc

Morphology

On postmortem examination, there are some differences between how stroke appears. you can have a haemorrhagic and nonhaemorrhagic ischaemic stroke, depending on how the infarct is reperfused. Haemorrhagic ischamic stroke is is characterised by multiple petechial haemorrhages and is due to reperfusion of damaged tissue after the event through collateral circulation, or following fibrinolysis of thromboembolis material in the occluded vessels and leakage of blood through necrotic vessels. This is usually associated with embolic ischaemic stroke

Nonhaemorrhagic ischaemic stroke has no reperfusion to necrotic vessels and is usually associated with thrombotic ischaemic stroke

Haemorrhagic stroke

This is found in 20% of strokes and can either be hypertensive intracerebral bleeding or subarachnoid haemorrhage (rupture of aneurysm)

Hypertensive intracerebral bleeding

This finish

Subarachnoid haemorrhage

Clinical aspects of stroke

Ischaemic and haemorrhagic stroke are treated very differently, as with ischaemic stroke you typically want to use thrombolytic therapy and this will make haemorrhagic stroke worse.

There is not much therapy for haemorrhagic stroke,

The penumbra is an area around the ischaemic area which may be saved on reperfusion, however as time progresses less and less are saved. Seconds are neurons in this care

Symptoms of ischaemic stroke

The symptoms of stroke depend on the size and location of the infarct with the somatotopic map of brain showing what may be effected with different infarct locations. Additionally the deep MCA branches supply the upper half of the internal capsule which may be effected in stroke, leading to complete hemiparesis

Brain edema

Tissue necrosis triggers inflammation which, along with loss of structural integrity can lead to disruption of the blood brain barrier. this can result in edema in the brain leading to higher ICP. Additionally blood is an irritant which can lead to more problems.

Treatment of stroke

To treat a stroke you must need to know the criteria used to diagnose a TIA / Ischaemic stroke and then the reasons to exclude haemorrhagic stroke and mimics before intervention.

The taught interventions are:

• Primary prevention
• Secondary preventions
• Acute interventions

Primary prevention

This is lifestyle changes which will lead to reduction in CVA risk. These are not trivial, as majority of stroke patients you will see are

Secondary interventions

After someone has a TIA or a stroke, its important for them to understand that this means their risk of future strokes have massively increased, and that they need to start on secondary prevention.

This is mainly how to reduce factors which can lead to stroke, such as Atrial fibrillation. vascular atherosclerosis. etc

The drugs associated with secondary prevention are expected to be known and will be detailed.

Acute intervention

The acute intervention in TIAs and Ischaemic cerebral infarction are surgical or pharmacological means, and the pharmacological means will be detailed.

The Pharmocological treatment regime is

• Fibrinolytics
• insulin + paracetamol to decrease blood sugar to

Fibrinolytics

These are recombinant tissue plasminogen activation

Treatment of haemorrhagic stroke

There is none.

We dont really have much we can do in haemorrhagic stroke, for acute cases we can give conservative treatment, or surgically evacuate the haemorrhage/clip or coil the aneurysm from which it burst, but otherwise there isnt much we can do.

There is possible use of factor VIIa to induce clotting, however trial results are disappointing, and while there was reduced haematoma, survival and functional outcome was not improved

Secondary prevention of these include:

• Antihypertensives

• Antidyslipidaemics

• Additionally

  • Nimodipine to precent vasospasm (also may have a neuroprotective effect due to lowering Ca2+)
  • Glycaemic control (neuroprotective and high blood sugar is unhealthy for nerves.)