One in three heart attack cases 'misdiagnosed'

BBC News reports a "third [of people] given wrong initial heart attack diagnosis", while The Sun makes the totally unsupported claim that "Doctors miss heart attacks in women 'because they expect victims to be fat, middle-aged men'."

These headlines are based on a study that analysed a database containing information about nearly 600,000 people in the UK who had been diagnosed with a heart attack over a nine-year period.

Researchers were particularly interested in how a change in the initial and later diagnosis was associated with survival. Overall, a third of people were given the wrong diagnosis initially.

Factors associated with being given the wrong diagnosis were being elderly (over the age of 83), having heart failure and atypical test findings, and – surprisingly – being female. Men were about a third less likely than women to have the wrong diagnosis to start with.

However, this is only observational data. It doesn't look into each individual case and give reasons for the wrong diagnosis or the gender discrepancy, despite what The Sun says. It also can't be assumed that all of these cases are down to clinical errors.

Nevertheless, there is a definite need to now examine the possible reasons behind these results in more depth to ensure people receive the correct care and treatment they need as soon as possible, and maximise the chances of a good outcome.

Where did the story come from?

The study was carried out by researchers from the University of Leeds and other institutions in the UK, and was funded by the British Heart Foundation and the National Institute for Health Research.

It was published in the peer-reviewed European Heart Journal – Acute Cardiovascular Care.

The study builds on previous work looking at whether clinicians were following best practice when dealing with non-ST segment elevation myocardial infarction (NSTEMI) type of heart attacks.

We discussed this research earlier this year.

The UK media's reporting of the study was generally accurate, but many of the headlines were speculative.

What kind of research was this?

This cohort study aimed to look at the impact of an initial diagnosis of a heart attack in hospital on outcomes.

There are different types of heart attack. The "classic" heart attack most people would be familiar with is medically called ST-elevation myocardial infarction (STEMI).

This is when the person has signs and symptoms of a heart attack, raised heart enzymes on blood test, and elevation of the ST segment on an electrocardiogram (ECG).

Non-ST elevation myocardial infarction (NSTEMI) is where the person similarly has the classic signs and symptoms and blood test findings, but lacks the ST elevation on ECG that indicates a heart artery has been completely blocked.

The two types of heart attack are managed slightly differently. If STEMI is diagnosed early enough, the person can be given clot-busting medication.

Sometimes immediate percutaneous coronary intervention (PCI), where a dye is injected to look at the heart arteries, is combined with breaking up the clot and putting in a flexible metal mesh called a stent to hold the artery open.

An NSTEMI is mainly managed with various medications, but coronary intervention may also be planned at an early stage.

This cohort study used a large quantity of data from a research database to look at how the initial diagnosis – STEMI or NSTEMI – impacted survival.

What did the research involve?

The study used data from the Myocardial Ischaemia National Audit Project, which included data for 564,412 adults (average age 68, two-thirds male) with STEMI or NSTEMI treated across 243 NHS hospitals in England and Wales between 2004 and 2013.

The researchers used the audit registry to look at the socio-demographics, medical history, clinical presentation and management of these people, including acute treatment at presentation – for example, clot-busting drugs or PCI – and longer-term medications.

The initial diagnosis was given by the treating consultant or medical team. The researchers confirmed this by looking at the European Society of Cardiology, American College of Cardiology and American Heart Association guideline definitions.

They looked at how the diagnosis changed as a result of subsequent tests and findings.

The main outcome of interest was death from any cause one year after hospital discharge, specifically analysing the effect of age and gender.

What were the basic results?

Overall, 29.9% of the cohort (168,534) had the wrong diagnosis initially.

Characteristics associated with having a STEMI but being wrongly diagnosed initially (either NSTEMI or other chest pain) were ST-depression at presentation, older age (over 83), fast heart rate and having heart failure.

People who had been misdiagnosed often missed out on having immediate aspirin or clot-busting treatment.

Similarly, being an older age, having a fast heart rate and heart failure were also associated with people with NSTEMI being wrongly diagnosed initially. These people often missed out on having coronary angiography.

Men were also significantly less likely than women to be wrongly diagnosed initially.

Compared with women, men had 37% reduced odds of having a wrong diagnosis if they had a STEMI, and 29% reduced odds of being given a wrong diagnosis of NSTEMI.

Pre-hospital ECG was associated with a good chance of having the correct diagnosis.

At one year, the death rate for people with STEMI was 5.6%, compared with 8.4% among those wrongly diagnosed as NSTEMI initially.

NSTEMI patients had 10.7% mortality, but it was 25.5% for those who were not correctly diagnosed with NSTEMI initially.

Overall, however, after adjusting for other factors, having a STEMI and being wrongly diagnosed initially (either NSTEMI or other chest pain) was not associated with significant reduction in time to death.

For NSTEMI, being wrongly diagnosed as having a STEMI was associated with a 10% reduction in time to death (time ratio 0.90, 95% confidence interval [CI] 0.83 to 0.97), as was other initial diagnosis (0.86, 95% CI 0.84 to 0.88).

The researchers calculated that if the 3.3% of patients with STEMI and 17.9% of patients with NSTEMI who were given the wrong diagnosis had been diagnosed accurately, between 33 and 218 deaths a year might have been prevented respectively.

How did the researchers interpret the results?

The researchers concluded that, "Nearly one in three patients with acute myocardial infarction had other diagnoses at first medical contact …

"There is substantial potential, greater for NSTEMI than STEMI, to improve outcomes through earlier and more accurate diagnosis of acute myocardial infarction."

Conclusion

This valuable audit looks at nine years' worth of data from NHS hospitals, finding about a third of people with two forms of heart attack – STEMI and NSTEMI – are often wrongly diagnosed initially.

These people are less likely to receive the guideline-indicated treatments they need – and the delay in receiving correct treatment could have a harmful effect.

The study also highlights the factors associated with a wrong diagnosis, including being of an older age, having heart failure, and atypical findings for either diagnosis. Unexpectedly, gender was also associated with a wrong initial diagnosis for women.

The study's findings are based on a very large database and mortality data came from the Office for National Statistics, so information on patient characteristics, presentation and deaths is likely to be fairly reliable.

However, the data has a few limitations. As the researchers say, there was some missing information in some cases, such as timing of the blood test to check the heart enzymes.

They also didn't have much detail on those who were given initial diagnoses of "other" chest pain.

Additionally, the researchers excluded people who died in hospital because they were uncertain of the treatments they were given beforehand.

In doing this they may, as they acknowledge, have underestimated the effects of changing diagnosis because the risk of death from a heart attack is highest in the early stages.

Also, the database does not contain complete data for all people who have had a heart attack in the UK.

This is only observational data, and you can't look in-depth into each individual case and find out exactly why the person was diagnosed and managed in the way they were.

As such, it is difficult to pin definite causes on this and explain reasons for the wrong diagnosis and gender discrepancy.

It may be that because being a man is a known risk factor for heart attack, the diagnosis may be more likely to be missed in women or thought to be other things – but this shouldn't be assumed.

Neither should it automatically be assumed that all of these wrong diagnoses were down to errors on the part of the care system or health professionals.

For example, in some cases the person may have immediately received all the diagnostic examinations, tests and treatments indicated initially, but their condition, signs and symptoms may have evolved over time.

You can reduce your risk of having a heart attack by having a healthy diet, maintaining a healthy weight, taking regular physical exercise within your limits, and stopping smoking.