MRC Cardiovascular Disease Research

By Prof A D MBewu

Interim President Medical Research Council

Specialist Cardiologist and Physician

Visiting Professor in Cardiology and Internal Medicine, UCT

April 6, 2005

Defintions

Atherosclerosis, meaning literally ‘hardening of the arteries’, is the most important form of cardiovascular disease (CVD). It is a degenerative and inflammatory disease of one of the largest organs in the body : the lining of the arterial blood vessels.

It has the same risk factors wherever the vasculature is found in the body, though its clinical manifestations may differ according to the organ – often predicated upon factors such as differing blood pressures in different parts of the body.

Since CVD is a single disease process, its clinical manifestations are the clinical sequelae of one disease process. They include :

  1. Angina pectoris and myocardial infarction
  2. Cerebrovascular accidents (CVA – strokes, reversible ischaemic neurological deficits etc) and
  3. Multiinfarct dementia
  4. Peripheral vascular disease (PVD) including renovascular disease

Atherosclerosis

Atherosclerosis is a degenerative and inflammatory process that begins in childhood with the formation of ‘fatty streaks’ within the endothelium – collections of cholesterol ester laden macrophages in the innermost lining of the blood vessels. Initially these are transient but with time more permanent abnormalities arise, with the fatty streaks (it is thought) progressing to plaques which impinge upon and may occlude the blood vessel.

The aetiology and pathophysiology of atherosclerosis is still poorly understood despite the investment of hundreds of billions of dollars in research over the past 50 years. Nevertheless the risk factors and determinants for this disease are known and have been demonstrated to be causal factors in both clinical studies and population-based observational and prevention studies.

Whatismore, modifying these risk factors and determinants can have dramatic effects on the incidence (new cases) and prevalence of heart disease and stroke.

Risk Factors and Determinants

Determinants are the proximal causes of the risk factors that in turn cause CVD. The classical risk factors of CVD are :

  1. Smoking – accounting for up to 25% of risk of CVD in populations
  2. High blood pressure – 20% of risk of CVD
  3. Dietary fats – high intake of saturated fats, transsaturated fats and cholesterol
  4. - low intake of monounsaturated fats (such as olive oil),

    polyunsaturated fats and omega-3 (marine) oils .

    - up to 30% of risk of CVD

  5. Other nutritional factors such as low intake of fresh fruit and vegetables probably because of the lack this entails of antioxidants such as alpha tocopherol (vitamin E), vitamin C, folate etc – up to 20% of risk of CVD
  6. Diabetes and prediabetes – 25% of risk of CVD in those afflicted

Prevention of Cardiovascular Disease

Smoking

It can be seen that smoking is the most easily avoidable risk factor. It is the most important cause of death in the world, accounting for 5 million of the 57 million deaths worldwide – primarily through causing heart attacks and strokes. In South Africa smoking accounts for more than 25 000 deaths per annum – roughly 5% of the total.

Smoking is best dealt with through health promotive interventions such as legislation banning smoking in public places, as well as through individual smoking cessation programmes. Conservatively it is estimated that such interventions alone could save South Africa R 300 million per annum.

High Blood Pressure

Hypertension afflicts over 25% of adult South Africans – yet is easily preventable through health promotive interventions such as reducing, through legislation the amount of salt added to processed food as this accounts for up to 80% of daily salt intake.

Furthermore screening programmes to detect and treat hypertension are relatively easy and cost effective meaning that dealing with this risk factor alone could avert 25% of CVD deaths per annum – or save 20 000 lives.

Economic Impact of CVD Prevention

The last econometric analysis of the economic costs of CVD to South Africa was performed nearly 10 years ago by Pestana and Steyn and came to a figure of R 4 billion per annum.

Since then the figure has probably risen to nearer R 10 billion per annum due to the emergence of an epidemic of CVD. At nearly 1% of GDP this means that the economic costs of CVD are on a par with that of HIV and AIDS.

As up to 80% of CVD deaths are avoidable (being deferred by 10 to 40 years till the person dies of some other cause such as Alzheimers Disease), CVD prevention can gain enormous benefits to a society – as can be seen in the USA and Europe where the CVD death rate has been halved between 1960 and 1990.

The age standardized death rates for CVD in South Africa are amongst the highest in the world, exceeding those of countries such as Scotland and Finland. Though deaths from infectious disease (HIV, TB and pneumonia) and violent injury are the commonest modes of death in those who die before the age of 45 in South Africa; CVD becomes the commonest cause of death after 45 years of age.

The greatest potential impact of CVD prevention on the fiscus is however not through lives saved but through disability averted. This is because patients with CVD often live for many years after their first cardiovascular event; requiring expensive medical and surgical interventions to treat their heart failure, stroke handicap etc. Furthermore, as with AIDS, most patients do not actually return to a fully active life, such as working down a mine shaft – depriving society of their economic input; often at a relatively young age such as 35 to 55.

Thus mild angina pectoris has an annual mortality of around 2 – 4 % (compared to 1 – 2% for the general population); whilst the annual mortality for heart failure at 15% per annum is similar to that for AIDS treated with antiretrovirals.

Human Impact of CVD Prevention

Furthermore, because CVD deaths in 2001 accounted for at least 88 000 (17% and possibly as much as 25%) of deaths in South Africa – CVD prevention has the potential to prevent up to 80% of these deaths – i.e. save 60 000 lives per annum (Appendix One). This is in stark contrast to the treatment of HIV and AIDS where current interventions prolong rather than lives; with patients generally surviving for several years after initiation of therapy.

Globally, Sir Richard Peto estimates that tobacco killed 50 million people in the last half of the 20th century – more than the number that died in the Second World War; and the majority of these were CVD deaths not lung cancer deaths. In this century Peto estimates, at current rates of smoking uptake in developing countries such as China and India tobacco will kill one billion people unless preventive measures are taken. The current 5 million annual deaths from tobacco compare with the 3 million from AIDS making tobacco, as MBewu puts it, the greatest public health disaster since the bubonic plague that decimated one third of Europe.in the 15th century.

A Cardiovascular Disease Research Lead Programme

Since CVD accounts for 17% of deaths and 25% of DALYs (mortality plus morbidity); and has great economic and social impact – it is clear that the MRC should be investing considerable resources in CVD research – perhaps up to 20% of its baseline direct research expenditure or R 20 million. Currently the figure is nearer R 10 million, principally through 2 of the 28 research units - though some CVD research is also done in the Health Promotion Research and Development Group through areas such as tobacco control and youth risk behaviour. In particular, the MRC should increase its investment in CVD prevention which has great potential to save lives, avert deaths and improve quality of life through preventing disability.