applying high sensitivity troponin in suspected m.i.

N Engl J Med 2019;380:2529-40
(Hard copy available in hospital library, online access via library website from next month.  Or register at NEJM.org to get free access to 3 'closed' papers a month.

Application of High-Sensitivity Troponin in Suspected Myocardial Infarction.  Neumann JT, Twerenbold R, Ojeda F et al. June 27th 2019

​I can't remember how I came across this study, but I read it hoping it may inform what I currently do in ED - which is use the 2015 European Society of Cardiology guidelines (here, well worth a read, figure 2 sums up biomarker use).  Well, most of the time.  Gestalt still plays a role.

I'm not doing a 'full' appraisal this time - so feel free to offer one via the comments.  In short, it's a part Roche and Abbott bankrolled (I'm pretty sure) mega study that aggregates prospectively obtained individual patient data from 15 US/Australasian/European studies.  These patients were 'suspected of having MI' clinically, and had 2 or more troponins done (I or T, high sensitivity).  STEMI patients were excluded.  The study includes data for 22,650 patients, 9604 in the derivation study, and 13407 in the validation study, obviously this is key in a paper studying a test.  There was a 15% prevalence of NSTEMI overall - I don't know what 'our' point prevalence is but this sounds about right.  

The aim of the study is great - it aspires to be able to do away with rigid troponin-taking protocols (e.g. time 0 and time +1/2/3 whatever hours) and risk stratify your patient whatever data you have for them.  You do need 2 results however.  They grouped these results into 'early' - 0 and <2 hours, and 'late' - 0 and >2 hours 1 minute.

Their stats are bound to be complicated given study size, and I don't really understand how they got there, so I can't question their process.  But essentially they looked at multiple cutoff ranges to define 'low risk' and 'high risk' of death or MI at 30 days.  Most of the conglomerated studies recorded this - some went out as far as 2 years.    But death or MI at 30 days is certainly an outcome of interest to a risk-stratifying emergency physician.

They then developed hard to understand (for me, anyway) 'compasses' or wheels so you can take a patient's initial troponin, interval change, and work outwards to a 'proportion of patients who are low risk if below those figures' and eventually a risk of death or MI at a month.  Your patient will 'fit' into either the low, or the high, risk compass.  I think, from playing around with various hypothetical patients.

www.compass-mi.com is their website with an algorithm where you can plug in your data sets.  This is helpful, and  easier to do than trying to fit your patient onto one of the compasses, but it's confused me further as it seems to only make them 'low risk' if the results are below the figures you have for your patient... it gives a risk of being high risk, rather than stratifying them for you, if that makes any sense at all. 

​Perhaps it's my simple ED brain, but this isn't terribly helpful and won't impact my practice.  Maybe it should - I've invited 2 cardiologists to comment.
I'd love to know your thoughts as an ED team member too, please click on 'comment' just below the title, I'll validate it once submitted and add to the thread - they aren't published immediately to reduce spam.
Thanks!
~Lou Mitchell~