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Stroke and Cryptogenic Stroke

What is a stroke?

A stroke occurs when the blood flow to an area of the brain is reduced.  This decreases the amount of oxygen being delivered to that area and results in some form of neurological impairment.  The nature of the impairment is dictated by the area of the brain that is affected and common examples are speech or visual disturbance or unilateral limb/muscle weakness.

The vast majority of strokes are ischaemic, which means that the blood flow in a vessel is reduced due to an obstruction (such as a blood clot or tear in the vessel wall).  They can, however, also be caused by haemorrhage, which is when a vessel bleeds into the surrounding brain tissue.

What is a TIA?

When the neurological impairment is short lived this is termed a Transient Ischaemic Attack (TIA or “mini-stroke). These are just as important as a full-blown stroke and may lead to a more serious event without appropriate treatment.

What causes an ischaemic stroke?

More common causes of ischaemic stroke are:

  • Atherosclerotic disease of the major arteries in the head and neck (e.g. carotid artery stenosis). This is when a build-up of cholesterol and calcium within the vessel wall predisposes to the formation of clots which can then be carried into the smaller vessels in the brain and cause obstruction.
  • Small vessel disease.  The smaller vessels within the brain itself can be chronically damaged due to such factors as high blood pressure, diabetes and smoking. This can lead them to block off and characteristically causes smaller strokes deep within the brain tissue.
  • Atrial fibrillation (AF) is one of the more common cardiac causes of stroke.  It is one of the most frequently seen abnormal heart rhythms and becomes more common as we age.  It results in irregular beating of the top (collecting) chambers of the heart and this can lead to the formation of clots within the heart that can then travel to the vessels in the brain.

Other causes such as blood clotting abnormalities can lead to abnormal clot formation anywhere in the body, and this may manifest as a stroke.  Also, a tear (dissection) in the vessel wall can cause reduction in blood flow.

A brain MRI scan (left) and Perfusion CT (right) in patients with different locations of stroke. The orientation is as though you are looking up at the brain from the patient’s feet, with them lying supine. The stroke on the MRI scan is the bright area in the lower aspect of the picture. This is in the left occipital lobe (at the back of the head). The CT perfusion scan demonstrates reduced blood flow in the red area (left fronto-parietal).

What is a cryptogenic stroke?

A cryptogenic stroke is essentially one where the cause of stroke is not clear and the most common causes, such as many of those mentioned above, have been ruled out. Cryptogenic stroke is more common in the younger stroke population (<65), and in those without traditional vascular risk factors. In that group an important cardiac cause is a patent foramen ovale (PFO).

What are the likely investigations required after a stroke?

The initial investigations undertaken after a stroke will usually be co-ordinated by a neurologist or stroke specialist. These will include Computed Tomography (CT) and Magnetic resonance imaging (MRI) of the brain, it’s vessels and the larger supplying vessels in the head and neck.  A number of blood tests will be performed, and this will include routine measures of kidney and liver function and also specific tests to look for diabetes, cholesterol levels and clotting function.

A baseline Electrocardiogram will be taken as an initial assessment for underlying heart problems and to check for Atrial Fibrillation.  If AF is not diagnosed on the baseline ECG a portable heart monitor may be arranged. This is because AF can come and go (paroxysmal AF) and so a single ECG may miss this.  There are different types of monitor and they may be worn for anything from 24 hours to a week or more.  Longer term monitoring may be required and can be done with an implantable loop recorder or LinQ device.

A Transthoracic Echocardiogram will also usually be arranged to look for any structural abnormalities of the heart.

At this stage a Cardiologist may get involved in order to tailor more specific cardiac investigations. These may include a bubble study to assess for a Patent Foramen ovale and a Transoesophageal echo to assess for any other source of clots within the heart.

What treatment options are available?

Almost all patients will initially be placed on antiplatelet therapy which will most commonly be Aspirin or similar. Cholesterol lowering medications (statins) are also very commonly used and there is evidence to suggest these are beneficial after a stroke even in the absence of significantly elevated cholesterol levels.  Further treatment will depend on what is found from investigation.

If AF is found stronger anticoagulation (blood thinning) medication will be required, and with newer medications now available, named Direct Oral anticoagulants (DOACS), regular blood test monitoring is not required.

If a PFO is detected, then a PFO closure procedure may reduce the risk of a further event.  PFO closure is a low-risk procedure that is performed on a day case basis with a catheter based (minimally invasive) technique.

If we find a narrowing in your neck blood vessel you may need surgery (Carotid endarterectomy) or stenting (Carotid artery stenting).

If you would like to arrange a consultation to discuss any of these issues, or for a cardiac assessment after a stroke please contact us.