Preventing coronary heart disease begins by understanding atherosclerosis, writes DR KHOO KAH LIN

THIS month, the World Heart Federation will be celebrating World Heart Day 2008 with the theme “Know Your Risk".

World Heart Day is a major event in Malaysia, too, with Yayasan Jantung Malaysia (YJM) leading the celebrations through the Yayasan Jantung Malaysia Healthy Heart Programme, which is supported by Quaker.

To care for your heart, one needs to know it first.

For starters, know the arteries, which are thick-walled muscles that carry the blood from the heart to the rest of the body.
The inner lining of an artery is called the endothelium. It contains cells that secrete substances to keep the artery in good working condition. They enable the artery to dilate and contract according to the volume of blood flowing through, and have an anti-thrombotic surface that discourages the formation of clots.

Unfortunately, the endothelium can become dysfunctional and lead to atherosclerosis, a condition characterised by the thickening of the endothelium. This causes the space inside the artery to narrow and flow of blood to become restricted.

Known risk factors for atherosclerosis, including raised plasma lipids (fats in the blood), diabetes, hypertension (high blood pressure), smoking and advancing age, are directly related to the degree of endothelial impairment.

HOW ATHEROSCLEROSIS DEVELOPS

The artery wall consists of three distinct layers — the intima, the media and the advantitia. In atherosclerosis, a series of bad changes occur, particularly in the intima. The process is called atherogenesis, and happens through:

- INVASION: When damaged, the endothelium become more permeable, making it easier for inflammatory cells and lipoproteins (especially partially oxidised LDL-cholesterol) to penetrate the inner lining and get inside the intima.

- RESPONSE: In response to these “foreign invaders", the endothelial cells start producing more adhesion molecules (i.e. proteins involved in the binding of other cells) to attract and carry more monocytes (a type of white blood cell) to the affected sites. Inside the intima, the monocytes transform into macrophage cells to “eat up” the invaders. Upon consuming them, the macrophages become foam cells, which subsequently combine with T-lymphocytes (another type of white blood cell) to form fatty streaks in the artery wall.

- REPAIR: But the battle isn’t over. Recognising the invasion as an injurious act, (the engorged foam cells is then transformed to foam cells which burst and causes an inflammation), the body sends in the repair team to the site.

White blood cells, called activated inflammatory cell, move to the site while the dysfunctional endothelial cells secrete growth factors (i.e. proteins involved in cell differentiation and growth). These increase the migration of vascular smooth muscle cells (VSMC) from the media to the intima.

During the journey, VSMC change from a “contractile” to a “repair” functional characteristic. The VSMC produce extracellular matrix materials that build an advanced atherosclerotic plaque to encapsulate the lipid-rich core.

- STABILISATION: VSMC make a fibrous cap to stabilise the atherosclerotic plaque against the pressure of blood coursing through the artery. A stable atherosclerotic plaque is less likely to rupture. It will have a thick fibrous cap with a high VSMC and collagen content, a relatively small lipid-rich core and low inflammatory cell content.

Unfortunately, the unstable atherosclerotic plaque is vulnerable to rupture. It usually has a thin fibrous cap with low concentration of collagen and VSMCs, a large lipid core (exceeding 40 per cent of the plaque volume) and high inflammatory cell content.

Unstable or vulnerable atherosclerotic plaques carry high risk of rupture and are responsible for the vast majority of acute clinical symptoms, such as angina (chest pain) and myocardial infarction (heart attack).

ASSESSING RISK OF CORONARY EVENTS

Angiography is a procedure that involves injecting a radioactive dye into the blood so that the blood vessels can be viewed on X-ray.

Coronary angiography is performed only on patients who show advanced symptoms and in whom arterial stenosis (abnormal narrowing of the arteries) is practically inevitable. Coronary angiography is unable to predict the risk of coronary events (eg a heart attack).

It does not provide information regarding plaque composition and is therefore unable to distinguish between a stable and unstable lesion.

Intravascular Ultrasound (IVUS) is a better technique to distinguish the lipid content in plaque. It is a medical imaging methodology using a specially designed catheter with an attached miniaturised ultrasound probe. It allows us to see inside blood vessels, through the surrounding blood column and visualise the endothelium.

TREATING ATHEROSCLEROSIS

Atherosclerosis is multifactorial; different factors may contribute to its development in different individuals. It is also a dynamic process; the rate of progression is determined between inflammatory and stabilising influences.

Medication and lifestyle modifications are required to treat atherosclerosis.

One treatment is to decrease the intensity or concentration of triggers by treating dyslipidaemia with lipid lowering drugs, controlling diabetes, prescribing ACE inhibitor, antioxidants, and homocysteine treatment.

Another treatment for atherosclerosis is to decrease sensitivity of the system by prescribing Omega 3, eNOS, oestrogens & ERMs (Estrogen Response Module), CCB (calcium channel blocker) and zinc.

A third strategy is to achieve regression of atherosclerosis by prescribing Rosuvastatin, Pioglitazone and/or Amlodipine.

LIFESTYLE CHANGES

Understanding atherosclerosis better can help you take care of your blood vessels and prevent clogged arteries.

You can also take it one step further by knowing you risk factors. Stop unhealthy lifestyle practices such as:

- Smoking or tobacco use decreases the level of HDL-C and increases the level of LDL-C in the body. Cigarettes are also loaded with “free radicals” that oxidises the LDL cholesterol that gets absorbed into the blood vessels.

·- Eating unhealthy food has a direct link to heart disease as it increases the risk factors, such as cholesterol levels, glucose levels and blood pressure and obesity.

- Regular aerobic exercises (brisk walking) for at least 30 minutes a day on most days are recommended. Also have a diet that is low in total fat (30g daily) in the form of 10 per cent saturated fat, 10 per cent polyunsaturated fat and 10 per cent monounsaturated fat.

Your diet should also be high in soluble fibre (more than 10g).

Soluble fibre (beta glucan) in the form of oats lowers cholesterol by binding them to the bile acids and preventing the cholesterol to be re-absorbed in the terminal ileum.

Hence, it lowers the level of circulating cholesterol. This lowers the risk of atherosclerosis as well.

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Article courtesy of the Healthy Heart Programme by The Heart Foundation of Malaysia supported by Quaker. Datuk Dr Khoo is a consultant cardiologist with the foundation