1 What are cardiovascular diseases?
1.4 Decline of cardiovascular diseases in Western society?
Cardiovascular diseases may be the main cause of death across most of the world, but the mortality (death) rates have actually been declining since the 1970s in most industrialised countries.
‘…CHD mortality decreased by more than 50% between 1981 and 2000 in England and Wales. Approximately 40% of the UK decrease was attributable to the combined effects of modern cardiological treatments and almost 60% to [a] reduction in major risk factors, particularly smoking. This is consistent with the majority of other studies in the United States, Europe, Scotland and New Zealand.’
For the USA, Figure 6 shows the decline in heart attacks in its population over 25 years to 2005. The reasons for all these declines are not straightforward, but may be due to improved prevention, diagnosis and treatment. These include:
- changes in cardiovascular risk factors, such as reduced smoking in adults, lower blood pressure and lower blood cholesterol levels
- development and access to medical treatments, such as thrombolysis, aspirin and statins, and surgical treatments, such as coronary artery bypass surgery and angioplasty to widen blocked blood vessels.
Figure 6: The numbers of heart attacks and surgical procedures (angioplasty and coronary bypass) per 10 000 of the population in the USA between 1980 and 2005 (Swanton and Frost, 2007)
Question: From Figure 6, you will see that, in 1990, 11 people per 10 000 of the population in the USA had angioplasty surgery. By 1995, this had increased to 17 people per 10 000. What was the figure in 2000?
About 37 people per 10 000 of the population had angioplasty surgery in 2000.
Although this decline in cardiovascular disease deaths sounds encouraging, the same researchers from the above quoted study also identified some adverse trends which would be expected to lead to more cardiovascular diseases in the future:
The adverse trends in obesity, diabetes, and physical inactivity together contributed ~8000 additional deaths in 2000. These canceled out 2 decades of improvement in cholesterol. Furthermore, continuing deteriorations are expected.
The 2005 statistics confirm that cardiovascular disease rates are falling in most northern, southern and western European countries, but the decline is slower or there is even an increase in central and eastern European countries (see Figure 7; Petersen et al., 2006). It is anticipated that over 80 per cent of the future increases in coronary heart disease will be in developing countries (Mackay and Mensah, 2004). The death rate from coronary heart disease is not falling so fast in South Asian people in the UK as in the rest of the UK population (Lip et al., 2007). So although many improvements have been made to the diagnosis, treatment and prevention of cardiovascular diseases, there is no time to be complacent: there are also other socioeconomic and risk factors at work that can just as easily reverse these encouraging declines.
Figure 7: The percentage change in coronary heart disease death rates in men and women aged 35 to 74 over a 10-year period (1988–1998) in selected countries
How confident can you be that statements of medical statistics are true – for example, ‘approximately 43% (43 men in every 100) of deaths in men in Europe are due to cardiovascular diseases'? What exactly do such statements mean? Identifying the cause of death is not an exact science, and medical practitioners may make a mistake. Moreover, there may be a greater tendency in some countries than others to identify the cause of death as a cardiovascular disease. Such effects can mask, accentuate or confuse genuine differences between countries in the occurrence of cardiovascular diseases. Often, such statements are more informative when a range is given, such as ‘30–50% of deaths in men are caused by cardiovascular diseases’. Such ranges may relate to true differences between countries, as well as to accuracy or bias in the diagnosis. It is important to look carefully at the meaning of such general statements to establish where and when they may be applicable.
Even given perfect diagnosis or data, statements on disease occurrence still require careful analysis if they are based on a sample of the whole population. For example, if a statement is made concerning smokers and is based on the incidence of cardiovascular diseases in a sample of 1000 smokers, can you be sure that the results seen with the sample of 1000 smokers apply to the whole population of smokers? This is where statistical methods are used which aim to show whether a result seen in a study is truly applicable to the population as a whole. These methods frequently generate a value called P (the P-value, a probability), which indicates how likely the result is to be wrong. For example, if you read that a study has shown that P < 0.01 (probability P less than 0.01), it shows that in more than 99 per cent of cases the results from the sample indicate what is happening in the wider population. The probability that the conclusions of the study do not apply – that is, they are incorrect for the population as a whole – is less than 1 per cent.