Strokes

Let me tell you about strokes. Strokes are the fourth leading cause of death in the UK and worldwide. There’s two main types of strokes. There’s thrombotic strokes and haemorrhagic strokes. Now, in thrombotic strokes an artery supplying the brain is blocked, but could be in the neck or inside the skull. Thrombotic strokes make up 80% of strokes in the UK. In a haemorrhagic stroke, a blood vessel inside the brain or surrounding the brain bursts, and they account for 20% of strokes in the UK, but in Asia, for instance, they are the majority of the types of strokes you get there.

It’s important to distinguish between the types of strokes, but, clinically, it’s difficult to do, so a doctor can’t look at a patient and say if it’s thrombotic or haemorrhagic. You need a scan to do this, either a CT scan, computed tomography, or an MRI scan, magnetic resonance imaging, so it’s important to get to a hospital as soon as possible and have a scan to try and find out what type of stroke it is. Thrombotic strokes can be caused in a number of ways. If an atherosclerotic lesion in an artery supplying the brain fissures, it can cause a thrombus to form, blocking the blood vessel, so part of the brain becomes short of blood.

What can also happen is that the atherosclerotic lesion fissures, a thrombus forms and then breaks off, and this travelling thrombus or embolus will move downstream, and it will lodge in a smaller blood vessel, blocking that blood vessel. Another way that they can form is when you get something called atrial fibrillation, and that’s when the heart is beating very fast, but ineffectively so the atria of the heart quiver. Now, this means that blood in the atria can stay there for longer, and a thrombus can form.

This can be swept as an embolus through the heart into the aorta and then up into a brain artery and lodge there and block it, so atrial fibrillation is a cause of strokes, and that’s why it’s got to be treated. Haemorrhagic strokes are caused when an artery bursts, and this can be an artery inside the brain, which is called an intracerebral haemorrhage, but can be an artery surrounding the brain. These are called subarachnoid haemorrhages, which get bleeding into the cerebrospinal fluid. The prognosis of haemorrhagic strokes is worse than thrombotic strokes, so, though they don’t cause all that many strokes in the UK, they’re actually more dangerous.

There’s something known as transient ischemic attacks or TIAs, which are sometimes known as mini-strokes. Now, this is when you may get showers of aggregated platelets that block the flow of blood to the brain for a short time, and they cause symptoms lasting just a few minutes normally, and there may be loss of brain function, so, for instance, you may feel dizzy. Now, these don’t cause any lasting damage, but very important, because if you’re getting transient ischemic attacks, it means you’re much more likely to get a full-blown stroke, so if you’re getting them, you must see your doctor and get some treatment. How are strokes treated?

Well, once you’ve had your scan, a CT scan or MRI scan in a hospital, if the scan shows you’ve got a thrombotic stroke, you can get treatment in the form of a protein being injected into your bloodstream. This is called tissue plasminogen activator or tPA. This causes an enzyme to be activated, called plasmin, and that breaks down the fibrin holding together the thrombus, so it will dissolve.

Now, it’s important that you get the scan and the treatment within four hours from the onset of the stroke. Otherwise it doesn’t work. And, in fact, less than 5% of people get tissue plasminogen activator because they don’t get to a hospital and have the scan done in time. So speed is very important.

If the scan shows that the type of stroke you’ve got is haemorrhagic, then there aren’t many treatments available, except for surgical techniques to open up the skull and then to surgically stop the bleeding, so we desperately need better treatments for strokes. That’s a big unmet need.