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Evidence matters: myocardial infarction

Study
Results
Comment

Of course, evidence itself is without effect. Putting evidence into action is when we should get the benefits. But do we? Demonstration that use of evidence makes a difference is something that many of us want to see. A report from Derbyshire [1] indicates that for mortality after heart attack, we are beginning to get big gains.

Study


This took place in the health district of South Derbyshire, which has a population of 560,000 with common computerised patient administration and pathology systems. All patients admitted with a coding of acute myocardial infarction over the five years of 1995 to 1999 were obtained, with information from the pathology system about measurements for creatine kinase. Excluded were patients with a coding of myocardial infarction but who had no creatine kinase measured, about 4% of the total. The pathology database was also interrogated for blood lipids in the year after the date of admission.

Results


There were 5,166 admissions over the five years, two thirds men and two thirds under 75 years old. Creatine kinase tests were requested on 4,912 of them, and 3,382 survived at least one year.

Within 30 days 396 died (13%), and within one year 585 died (19%). There was a 9% (95% confidence interval 4 to 13%) per year fall in the 30-day mortality, for men, women, and younger and older patients. For one-year mortality, the results suggest, though do not specifically state, that there was a 7% a year decline. Mortality was higher in women than men and for patients aged over 75 years compared with those aged between 35 and 74 years.

The proportion of one-year survivors having a blood lipid measurement increased over the five years, especially so in those over 75 years (Figure 1). Among those admitted, and who had a lipid measurement, the proportion whose latest total cholesterol measurement within 12 months of admission was below 5 mmol/L rose dramatically, though was lower for women than men (Figure 2). Similar trends were seen with respect to low density lipoprotein.

Figure 1: Having lipids measured within one year of infarction




Figure 2: Achieving target cholesterol reduction in 1995 and 1999




Comment


Year-on-year improvements like these are important. In South Derbyshire, the chance of a 50-year old man dying within the first year had fallen by about 30% in 1999 compared with 1995. This big improvement was brought about by many factors, and will probably be better in 2002 than it was in 1999. Over the five years as whole, one year mortality was 19%, and that has to be compared with 28-day mortality of up to about half in Glasgow in the 1980s.

Evidence from major outcome studies, like the 4S study with statins, has helped change practice. More people now have blood tests for lipids after a heart attack, and most meet targets for lowered cholesterol. This is just one factor underlying the improvements, but there will be others, including more use of aspirin, or beta-blockers, or ACE-inhibitors, and better cardiac rehabilitation, and better primary care attention.

It is not just one piece of evidence, but many pieces of good evidence used appropriately that continues to make a difference. We've come a long way, but with further to go. Evidence matters!

Reference:

  1. J Harrop et al. Improvements in total mortality and lipid levels after acute myocardial infarction in an English Health District (1995-1999). Heart 2002 87: 428-432.
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