Atherosclerosis

Synonyms: Arteriosclerosis, atheroma

Atherosclerosis is a condition affecting large and medium-sized arteries. It is characterised by the accumulation of various substances (see below) in the subendothelial space. This leads to the formation of atherosclerotic plaques and to other changes, which may eventually disrupt the blood flow to target organs.¹

The term comes from athere the Greek word meaning gruel, referring to the deposition within the arterial walls, and sclerosis meaning hardening which refers to the arterial intima.

In the artery's subendothelial space, there is an accumulation of: lipids, inflammatory cells, smooth muscle cells and extra-cellular matrix. This forms an atherosclerotic plaque, which progresses unpredictably to different stages.² Acute clinical events are due to plaque rupture and subsequent thrombosis.³

Although the disease tends to manifest itself in later life, its earliest phases are present in teenagers and young adults. The earliest lesion involves the intima of the artery and begins in childhood with the development of fatty streaks; these are present in most individuals by age 20 years.⁴

The early stages of atherosclerosis are asymptomatic and so its prevalence is difficult to determine accurately, though post-mortem studies give some estimates.⁵ The clinical manifestations of atherosclerosis, such as coronary heart disease (CHD), are common in Westernised and urbanized populations, and are an important and common cause of death and disease. CHD is less common in the Far East and in the rural developing world.¹

Many risk factors have been identified for atherosclerotic disease; the main ones are listed here. Note that most of the research on this topic relates to the clinical manifestations of atherosclerosis, as measured by rates of coronary heart disease, stroke or peripheral vascular disease. It is less clear from the literature, how far these risk factors relate to the underlying atheroma itself.

Atherosclerosis in its early stages is silent, but later may produce chronic or acute vascular diseases:

• Coronary heart disease: angina, or more acutely, the acute coronary syndromes of unstable angina or myocardial infarction
• Cerebrovascular disease, transient ischaemic attacks and stroke
• Peripheral vascular disease or acute limb ischaemia
• Aortic aneurysm
• Renovascular disease

Investigation of manifest cardiovascular diseases and of cardiovascular risk is covered under the relevant topics.

Investigation of atherosclerosis in its own right is not routine in clinical practice, but has been used as a research tool. Possible ways to assess asymptomatic atherosclerosis include:

• Ankle-brachial index¹⁴
• Ultrasound measurement of carotid intima-media thickness or flow-mediated dilation in the brachial artery¹⁵
• MRI techniques¹⁶

This involves:

• Treatment of any existing cardiovascular disease if necessary
• Modification of risk factors,¹⁷ using:
  • Lifestyle measures
  • Drug treatment where appropriate, e.g. statins

See Secondary Prevention of IHD.

Absolute prevention of atherosclerosis seems unlikely, given the early age at which it starts to develop. However, slowing the progression of atheroma seems possible; this may then prevent or delay the cardiovascular disease (CVD) consequences.

Note that much of the clinical research on this topic relates to prevention as measured by CVD endpoints, rather than atherosclerosis. Hence, the rest of this section may also relate more to CVD than to atherosclerosis specifically.

Prevention at population level

• Legislation and modifying the environment so as to promote healthy lifestyles, for example: anti-smoking legislation, town planning,¹⁸ promoting walking and cycling, food labelling and banning trans fats in food.¹⁹
• Child-parent screening for familial hypercholesterolaemia has been suggested²⁰ and discussed.²¹

Prevention for individuals

Current UK strategy, embodied in the National Service Framework, is to assess patients likely to be at high risk of cardiovascular disease. Healthy lifestyle advice should be given to all, and primary prevention offered to those above a certain risk threshold.

Assessment of cardiovascular disease risk

There are various cardiovascular disease risk scores available:

• Traditionally, the Framingham data were the basis of most scoring systems, including those used in many UK general practice computers.
• In 2005, the Joint British Societies' paper introduced new risk charts. These are found in the British National Formulary and are available in digital form.¹⁷
• The QRISK score may be better suited to the UK population.²²

Primary prevention of cardiovascular disease

See Primary Prevention of Cardiovascular Disease.

• There are established UK guidelines for primary prevention of CVD.^17,23
• However, the automatic application of these guidelines to all patients has been questioned (see editorial²⁴ and related comments.) For example, the guidelines use absolute CVD risk scores, thus putting most elderly patients into the "treat" category, despite the lack of trial data for the over-70s age group.
• For elderly people, prevention of CVD is not always a benefit, as it may select out CVD as a cause of death, in favour of other deaths such as cancer.²⁵