Yet more interesting reading from Dr Kendrick.
What causes heart disease part 61 – strokes
15th January 2019
In this never-ending story on heart disease, I have tended to use the terms “heart disease” and “cardiovascular disease” almost interchangeably. Well, everyone else does it, so why not me? However, in this blog I shall be splitting cardiovascular disease into its two main components, heart attacks and strokes, and concentrating mainly on strokes.
The first thing to say is that there are three main causes of strokes.
Atrial Fibrillation (ischaemic)
A burst blood vessel in the brain (haemorrhagic)
A blood clot (ischaemic)
[There are also cryptogenic strokes (no known cause), strokes due to a hole in the heart, strokes due to antiphospholipid syndrome, strokes due to sickle cell disease etc. etc.)
Atrial Fibrillation (AF) is a condition where the upper chambers of the heart (atria) do not contract and relax smoothly every second or so. Primarily because there is a disruption in the electrical conduction system, causing the atria to spasm and twitch in a highly irregular fashion.
When this happens, blood clots can form in the left atrium then break off and head up into the brain and get stuck. Causing a stroke. They can also travel elsewhere in the body causing a blockage to an artery in the kidneys, the leg, the arm and suchlike. If they form in the right atrium, they will end up stuck in the lungs.
These clots are usually quite small, about the size of a large grain of rice, but this is still big enough to do quite considerable damage. The treatment for AF is either to try and reverse the fibrillation or, if this does not work, to give anticoagulants such as warfarin to stop the clots forming.
A haemorrhagic stroke is when a blood vessel in the brain bursts. Blood is then forced into the brain and causes a lot of damage – leading to a stroke. Haemorrhagic strokes are usually quite severe, as you can imagine. The treatment is to NOT give an anti-coagulant of any sort. Haemorrhagic strokes are often/usually caused by a thinning of the artery wall, causing a ballooned area (aneurysm), which then bursts.
An interesting question, and I have seen different views on this is whether a small blood clot travels to the brain where it gets stuck, but does not completely block the artery, so it does not cause a stroke, but it creates an area of damage – which is then repaired – that leaves a weakness in the artery that balloons out – an aneurysm.
Anyway, the most common cause of a stroke is that large atherosclerotic plaques form in the main arteries that supply blood to the brain (carotid arteries). These plaques usually form around the base of the neck. A blood clot then forms on top of the plaque, then breaks off and travels to the brain, where it gets stuck – as with atrial fibrillation – causing a stroke. The effect is the same as with AF, but the underlying causing is completely different.
According to the American Stroke Association 87% of strokes are ischaemic.
Which means that the vast majority of strokes are caused by atherosclerotic plaques in the neck. Just as the vast majority of heart attacks are caused by atherosclerotic plaques in the coronary arteries. Therefore, you would expect that the risk factors for stroke would be exactly the same as the risk factors for heart attacks, as the underlying process is the same.
Well, many of the standard risk factors are the same. Smoking, diabetes, high blood pressure and suchlike. However, a raised LDL most certainly is not. There is a research study called the Simon Broome registry, started in the UK, that tracks the health outcomes of people diagnosed with familial hypercholesterolaemia (FH).
It is a fascinating resource which, if you decide to interpret their data through a different prism, virtually rules out the raised LDL in familial hypercholesterolaemia as a cause of CVD. One of the earlier papers in the BMJ, on the findings of the Simon Broome registry, found that:
Please continue reading herehttps://drmalcolmkendrick.org/2019/01/15/what-causes-heart-disease-part-61-strokes/
All the best Jan