Atherosclerosis – BASIC PATHOPHYSIOLOGY

Epidemiology
Cardiovascular disorders are the leading cause of death in western society

In England and Wales, they account for 40% of all deaths:
Ischaemic heart disease is 27%
Cerebral vascular disorders 13%.

Atherosclerosis is by far the most important cause
In the developed world the incidence has increased massively
In the US and some European countries, incidence has actually peaked and in declining
In the rest of Europe, and in the middle and far east, incidence is rising rapidly

Pathology

Atherosclerosis can have 3 main types of manifestation:
• Coronary heart disease – angina, MI, sudden death
• Cerebrovascular disease – stroke, TIA
• Peripheral vascular disease – claudication, critical limb disorder

These situations often co-exist, and the pathology is very similar. For example, patients presenting with stroke or claudication will very likely have coronary artery disease – and this co-existing disease is an important cause of mortality.

Normal artery structure:

There are 3 layers of arterial tissue:
Tunica Intima – this is the innermost layer, and has a single layer of endothelium, with a sparse supportive tissue. This layer is very very thin!
Tunica Media – this is separated from the intima by the internal elastic lamina. The media is made up of smooth muscle and elastic tissue.
In the heart, the elastic tissue is most predominant, but in most arteries, this layer is mostly made up of smooth muscle.
Tunica Adventitia – this is a fibrous connective tissue. The external elastic lamina separates this from the media. Very small blood vessels can be found in this layer called vasa vasorum and these filter down to supply the media.
The intima and innermost media receive their nutrients from the arterial lumen via diffusion.

Normal age-related changes
These will usually be inconsequential by age 40, and very common by age 70. They are often termed arteriosclerosis. the changes affect all blood vessels, right down to the arterioles.
They include:
Progressive fibrous thickening of the intima
Fibrosis and scarring of the muscular and elastic media
Accumulation of mucopolyysaccharide ground substance
Fragmentation of the elastic laminae

Ultimately these changes reduce the strength and elasticity of the vascular wall. Clinically, this will mean there is dilation of the aorta and coronary arteries – and this finding is common.
In the aorta this can lead to stretching of the aortic ring – resulting in valve incompetence
Dilation of the aortic arch and thoracic aorta can also lead to ‘unfolding’ of the aorta – which can be seen in chest x-rays as a loss of the aortic notch, and a widened appearance of the central vascular column in the x-ray.

To compensate for these changes, there is often smooth muscle hypertrophy and production of extra layers of collagen in the internal elastic laminae.

G.MOHAN

More to follow.