Sunday, 3 April 2016

A 1-hour rule out MI protocol in the era of high sensitive troponin assays; ready for prime time

Studies of the high sensitive troponin assays all demonstrate the same thing. Patients will rule-in for MI much quicker compared to the old conventional assays. The vast majority will do so within a few hours of onset of symptoms.

The lead author of this study, Dr Tobias Reichlin has been working his way down the impact factor ladder with his ongoing research. His most recent offer has been published in the Canadian Medical Association Journal. But don’t let this fool you. This study is important and the final nail in the coffin for the 3 or 6 hour rule-out. 

This multicentre study enrolled 1320 patients presenting to the ED with suspected MI. The algorithm they attempted to validate used a baseline and 1 hour high sensitive troponin T. They looked at the absolute values in addition changes at one hour. Two independent cardiologists adjudicated the final diagnosis with access to all of the information (including troponin values... so ok, there was some incorporation bias with the gold standard.)

Results: The sensitivity and the negative predictive value for ruling out MI was 99.6% and 99.9% respectively. This made up about 60% of their cohort. The rule-in rate was 17%. They also had an indeterminate category that only made up one quarter of the patients overall. I have cut and pasted the algorithm below.

These results are one in a long line of studies demonstrating the same thing. Consistency in the literature is always compelling. The time has come to change our local protocols to allow for the safe rapid rule-out strategy in suitable patients.

Having said this, there is one strong word of caution. Beware the early presenters. Common sense would dictate that the person developing chest pain in the parking lot of the hospital should not undergo a one hour rule-out.

Unfortunately, the manuscript of this paper did a terrible job of describing the proportion of the early presenters. A vague and unhelpful mention was made in the on-line only appendix.

Another contention was the “data snooped” cut-off’s of 12ng/ml and 52ng/ml as their low and high cut-off’s for rule-out or rule-in MI. Of course this came from the earlier derivation study, but I think that 14ng/ml and 50ng/ml should be just fine. This certainly should make it more user friendly without having a substantial impact on test characteristics. Of course this is just my opinion, so there might be differing opinions.

If you are waiting for the AHA/ACC to provide updated guidelines then don’t hold your breath. The Americans have been very slow adopters of the high sensitive troponin assays. It is now up to us to determine what is clearly ready for prime time.


Covering:

Reichlin T, Twerenbold R, Wildi K, et al. Prospective validation of a 1-hour algorithm to rule-out and rule-in acute myocardial infarction using a high sensitive cardiac troponin T assay. Can Med Ass J 2015;187:1-10. doi: 10.1503/cmaj.141349





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