Every now and again a Journal doesn’t want us to talk publically about our own paper until it they publish it. This is simply so they can make more of a splash with it. This was the case of an article I have been involved with published today in the Cardiology journal of the American Medical Association*.
What’s it about?
Ruling out a heart attack in the emergency department is difficult. Readers of this blog would have read about various other ways we’ve developed to be part of it (eg here). They depend on many things including the type of blood measurement used and the timing of that. These markers – called troponins – detect damage to the heart muscle.
In this study led by Ed Carlton of Southmead hospital in Bristol, UK, we evaluated whether a single measurement of very low levels of a comparatively new blood biomarker called “High-sensitivity troponin I” could alone rule out heart attacks within 30 days when someone presented to the emergency department with chest pain (Here Ed speak about the study here).
3155 patients at 5 hospitals in New Zealand (Christchurch), Australia and the UK participated of whom 291 had a heart attack (277 were having a heart attack on the day they presented to ED, the other 14 had one within 30 days).
We found that 594 (18.8%) of patients had such a high sensitivity troponin I concentration below the limit at which it could reliably be detected. ie next to nothing. These we can say tested negative. Three of them (0.5%) it turned out did have a heart attack.
Why the splash?
The editor got quite excited about this and another study and wrote an editorial to accompany the studies:
“To manage costs and the adverse effects of overcrowding in the ED, it is a high priority to rapidly and safely identify patients with a sufficiently low probability for acute coronary syndrome (<0.5%-1%) so that they can be discharged efficiently and avoid unnecessary testing.”
He was impressed that this study had been “tested in robustly sized, geographically diverse, clinically relevant populations.”
“Taken together with prior studies the findings from the studies of Neumann et al and Carlton et al lend strong support to the notion that accelerated diagnostic protocols that incorporate [high sensitivity troponins] can facilitate earlier triage while maintaining an acceptable [rate of false negatives].
One of the features of interest to the readers of this US journal is that the high-sensitivity troponins are not yet available in the US, however they eventually will be and how they are used is of particular interest.
Part of a figure from the publication showing how choosing different troponin thresholds to rule-out patients changes how sensitive the test is.
Why not perfection?
Of course we would love to never have a false negative (or false positive). However, the reality of medicine is that this is not possible. We could, of course, simply admit everyone, do more invasive tests, or “wait and see” if they develop a heart attack. There are, though, risks as well as costs with admitting people to hospitals. If I may speculate for a moment, the rise in superbugs resistant to antibiotics is only likely to increase those risks in the future – hence the importance of studies such as this. It is important that we get the balance of risk right.
What are the next steps?
All of New Zealand now has some kind of accelerated diagnostic pathway for chest pain patients that incorporates serial troponin measurements. At some stage we will implement, monitor, and measure the addition of an even more accelerated rule-out for some patients with just one troponin. Watch this space.
* Carlton, E., Greenslade, J., Cullen, L., Body, R., Than, M. P., Pickering, J. W., Aldous, S.A., Carley, S,. Hammett, C., Kendall, J., Kevill, B., Lord, S.J., Parsonage, W.A., Greaves, K. (2016). Low concentrations of high-sensitivity cardiac troponin I at presentation in the evaluation of emergency department patients with suspected acute coronary syndrome. JAMA Cardiology. http://doi.org/10.1001/jamacardio.2016.1309