Thursday January 26 2012
Fewer people are having heart attacks, and those that do are more likely to survive them
Heart attack deaths have halved in less than a decade, according to a major study of over 800,000 patients in England. The research has been extensively reported, with news sources suggesting a range of possible reasons, such as better treatments and a reduction in numbers of people smoking.
As the study itself points out, many developed countries have seen reductions in heart-related death over the last 40 years, but it is unclear whether the trend is due to better treatment following a heart attack or steps designed to prevent heart attacks in the first place. This new study found that in England the death rate from heart attacks halved between 2002 and 2010. The researchers calculated that just over half this decline was caused by fewer people having heart attacks and just under half by more people who had heart attacks surviving.
This major, well-conducted study indicates some good news – that fewer heart attacks have occurred in recent years and of those that did occur, fewer were fatal. This encouraging trend is seen in both sexes and all geographical regions. As the authors conclude, further research is needed to determine the specific factors that have resulted in these declines, but the evidence suggests that they are caused by healthier lifestyles, better prevention for those at risk and improved medical treatment for heart attack patients.
However, the findings are not all good news: the study also found that in contrast to the middle aged, heart attack rates have changed relatively little in both young people and the very old. They suggest that rising rates of obesity and diabetes in younger people may eventually contribute to a ‘levelling off’ of the decline in heart attack rates.
Where did the story come from?
The study was carried out by researchers from the University of Oxford’s Department of Public Health. The individual authors were funded by various institutions, including the Medical Research Council and the British Heart Foundation. Part of the research was funded by the National Institute for Health Research. The study was published in the peer-reviewed British Medical Journal. Newspapers generally covered the research accurately and appropriately.
What kind of research was this?
This study examined recent trends in heart attack rates and deaths from heart attacks, with specific focus on the influence of factors such as sex, age and geographical region. To do so it used information about heart attacks in over 800,000 people, taken from a national database of hospital and mortality records. It also looked at whether any drop in heart attack deaths was primarily due to those people having heart attacks now having a lower risk of dying, or whether it was due to fewer people now experiencing heart attacks.
The authors point out that while many developed countries have seen a decline in heart attack deaths since the 1970s, in England at least, reasons for this decline are not fully understood: it is hard to tell whether increased prevention or improved treatment is primarily responsible. Given this lack of clarity the researchers attempted to examine whether the trend was due to people having fewer heart attacks or to those having heart attacks being less likely to die.
What did the research involve?
The researchers obtained data from national datasets on both hospital admissions and mortality statistics. From this data they were able to include all residents in England who had had a heart attack (or acute myocardial infarction) between 2002 and 2010, as defined by diagnostic codes applied to patient records during treatment. They categorised heart attacks as either fatal (defined as death occurring within 30 days of admission) or non-fatal. To study regional differences they obtained regional data.
Using standard statistical methods they calculated both the new heart attack rate (incidence or event rates) and heart attack death rate (mortality rate) per 100,000 of the population. They did so according to age group and sex, and for each year and each region. They used these figures to calculate the changes in heart attack mortality rates during this period and also the relative contributions of ‘event rates’ (i.e. the number of heart attacks) and ‘case fatality rates’ (i.e. the number of deaths among people who had heart attacks).
What were the basic results?
The researchers found that from 2002-10 in England, 840,175 people of all ages were admitted to hospital with heart attack or died suddenly from a heart attack. Some 61% of heart attack patients were men, and 39% were women. The main findings are listed below:
- During this period the mortality rate from heart attacks fell by 50% in men and by 53% in women when the results were ‘age standardised’, i.e. adjusted to account for the changing age structure of the population.
- The greatest rate of decline in events occurred in men and women aged 65-74, and the lowest decline was among those aged 30-54 and 85 or older.
- In men, rates of heart attacks, deaths due to heart attack, and overall death all declined. The average annual rates of decline were, respectively, 4.8% (95% confidence interval [CI] 3.0% to 6.5%), 3.6% (CI 3.4% to 3.7%) and 8.6% (CI 5.4% to 11.6%).
- In women, the corresponding rate reductions were 4.5% (CI 1.7% to 7.1%), 4.2% (CI 4.0% to 4.3%) and 9.1% (CI 4.5% to 13.6%).
- The researchers then calculated how far the decline in heart attack deaths was caused by lower heart attack rates and how far by the chances of surviving after a heart attack. Reductions in the number of new cases were estimated to account for 57% of the reduction in deaths among men and 52% among women. The chance of surviving a heart attack was estimated to account for 43% of the drop in deaths in men, and 48% in women.
- The relative contributions of these two factors differed by age, sex and geographical region.
How did the researchers interpret the results?
They point out that just over half the decline in deaths from heart attacks over the period can be attributed to a fall in people experiencing heart attacks and just under half to improved survival rates when people did experience a heart attack.
However, the researchers say that it is possible there has been no ‘real improvement’ in heart attack rates in younger people and the very old. They say that rising rates of obesity and diabetes may be contributing to a ‘levelling off’ of the decline in numbers of heart attacks.
They suggest that the decline in the numbers of heart attacks could be explained by lifestyle changes and the use of preventative drugs in those at risk, although further research is needed to gain a clearer understanding of the specific elements of prevention and treatment that have contributed to the fall in death rates.
The strengths of this study lie in its very large size and its complete national coverage. One possible limitation is its reliance on the accuracy of routine data and diagnosis codes used from English hospitals, although, as the authors point out, research has shown high accuracy rates for this type of data.
It should be noted that although the study shows a fall in heart attacks and also in death rates among heart attack patients, it does not tell us the precise causes of either. The fall in heart attacks is likely to be linked to healthier lifestyles, earlier detection and a better management of risk factors such as high blood pressure in people at risk. Also, the study only examined deaths from heart attacks and the definition of this has changed over the years, so the researchers say that they could not report on changes in hospital admissions as the diagnostic coding for this has also changed.
Overall, while we cannot fully explain the drop in heart attack deaths observed in this report, the good news is that the trend is clearly going in the right direction.