Yesterday the NZ Herald published an article saying doctors are failing to spot heart attacks in thousands of women. This sounds alarming, could it be happening in NZ? Are women getting a raw deal? Important questions. This post looks at the study behind the media and then at how heart attacks are being diagnosed in New Zealand.
The Herald article is evidently based on press releases related to a study published to coincide with the European Society of Cardiologist’s conference currently underway in Rome and attended by some 30,000 cardiologists, other physicians, industry types, and the Pope (yep!). The study in question comes from the University of Leeds. Here’s the Leeds Uni press release.
The study is based on an audit of UK data collected about patients between 2004 and 2013 whose final diagnosis was a heart attack (in clinical jargon a myocardial infarction, either STEMI or NSTEMI). The full article is available here.
The subjects were patients who at discharge from hospital had a heart attack diagnosis. The authors looked at the preliminary diagnosis of patients when they first entered the hospital and compared that diagnosis to the final diagnosis of a heart attack. The preliminary diagnosis was for about a 30% of patients not explicitly a heart attack – ie often something like “chest pain of uncertain cause.” In the press release and news reports this was reported as a “misdiagnosis.”
Point 1: The term “misdiagnosis” is inappropriately applied here. While some forms of heart-attacks can be diagnosed in the ED, most can not. Indeed, the guidelines for diagnosis of a heart attack require some blood measurements at least 6 hours apart. Nowadays, the later blood sample is not done in the ED, but in a cardiology or general medicine ward. That is, the ED physicians often don’t have all the data to make a definitive diagnosis – hence only a preliminary diagnosis is made. Most of the time the job of the Emergency department physicians is to rule-out some possible diagnoses and to identify patients at significant risk of a heart attack. These patients are referred on to the specialist teams within the hospital who make the final diagnosis.* Yesterday I was speaking with a cardiologist who was explaining how often cardiologists themselves disagreed over a diagnosis. It ain’t easy.
The press releases and media reports emphasise that a larger proportion of women than men were likely to have a change between the preliminary and final diagnosis. The Leeds University press release states women were 59% for a final STEMI diagnosis and 41% for a final NSTEMI diagnosis more likely than men to have a change from the preliminary diagnosis.
Point 2: These numbers are not reported in the published paper! Nor is anything about the differences between men and women discussed in the paper. In the results section it is simply stated that those who had an initial diagnosis that changed were more likely to be older, female, and have a co-morbidity. There are some numbers related to this in a table. In the table I note that patients older than 61 compared with younger patients had at least (more if they were even older) the same odds of having a diagnosis changed as did females compared with males (it’s a little awkward in the paper because the odds ratio is written the opposite way around – but this can be rectified simply by taking the reciprocal of the odds ratio and comparing that). There were also other predictors of a change in diagnosis (eg higher heart rate). The cynic in me thinks that it may be for publicity reasons that the emphasis has been placed on the sex differences in press releases.
Point 3: What is important about the study is that in those who had a change in diagnosis the one-year mortality rates were higher. While the suggestion is made that this is because of delay in time to treatment (known from other studies to be important), there are other potential reasons because of the differences in demographics and co-morbidities between the groups.
The study began at a time when the blood biomarkers indicative of a heart attack that are used now (troponins) were not in common use. There have been several generations of markers, the latest of which are “high-sensitivity troponins.” The authors’ recommended that:
“…our results… call for the earlier use and wider adoption of high sensitivity troponins as well as a focus on the systematic application of accelerated diagnostic protocols using risk scores rather than subjective clinical assessment.”
The good news is that New Zealand is now the only country in the world** to have accelerated diagnostic protocols using risk scores in place in every ED. Furthermore, most ED’s are using the latest high sensitivity troponins.
In the Christchurch ED, different sex-specific thresholds of the troponin used for risk stratifying and diagnosing heart attacks are used. This is because in the general healthy population males have slightly higher values of these troponin measurements than females. Therefore, to avoid underdiagnoses of females a lower diagnostic threshold is used. Furthermore, in a study we were part of and lead by our Brisbane based colleagues, using sex-specific threshold helped improvs risk prediction for future adverse events in women.
In New Zealand it is less likely that women are getting a raw deal.
*perhaps the Pope a.k.a @Pontifix [literally the “bridge builder”] could help bridge the divide between ED physicians and cardiologists – generally ED physicians rule-out heart attacks, Cardiologists rule-in heart attacks.
** although Queensland also has this and they like to think of themselves as a country sometimes