Ruling out MI with a 0/1-hour high-sensitivity troponin protocol is safe and does not increase the risk of death or MI at 30 days when compared with standard testing over three hours, according to results from the Australian RAPID-TNT trial.

The randomised trial, which was presented at the European Society of Cardiology Congress, included 3,378 patients with suspected ACS presenting to four emergency departments in Adelaide. It was designed as a noninferiority study of the 0/1-hour protocol using hs-cTnT compared with a standard 0/3-hour protocol with troponin T results.

Compared to the standard protocol, patients in the 0/1-hour arm were significantly less likely to be admitted (45.5% versus 33.2%) and had a significantly shorter length of stay (5.6 versus 4.6 hours).

Speaking to the limbic from Paris, lead investigator on the study Professor Derek Chew said the findings confirm the protocol is safe for the early discharge of low-risk patients, noting that the event rate – death or MI at 30 days – was the same 1% in both groups.

“What we found was that patients clearly at lower risk are at lower risk and clinicians can safely send them home because there is no difference in the outcome of patients who were managed in the one-hour protocol versus the three-hour protocol.

“More importantly what we also saw was 72% of patients in the one-hour protocol received a recommendation that they could be discharged from Emergency and the event rate in those who were discharged was very very low, around 0.3%.”

The new protocol was also associated with less functional cardiac testing (7.5% vs 11.0%, P<0.001), but more myocardial injury – particularly acute injury and Type 4a and Type 5 MIs, which Professor Chew said stemmed from greater use of invasive coronary angiography and subsequent revascularisation in the subgroup of patients with troponin below 29 ng/L.

“Whether or not that’s warranted will really depend on what happens at 12 months, but what we did see is the more we instrument peoples arteries the more we lead to injury and myocardial infarction.”

He added that better strategies for the increased numbers of patients who are ‘ruled-in’ with this method – by having a positive or abnormal troponin reading – would need to be considered if overall outcomes are to be improved.

“The positive predictive value of a rule in or intermediate reading is less than 40% so in other words less than 40% of people who get an elevated troponin have a myocardial infarct.”

Professor Chew says what happens next for these patients needs some careful study and further decision support.

“Potentially not all of these patients need aggressive angiography. Maybe we need to explore other strategies such as CTCA for these patients.”

But he argues that’s not a reason not to allow the health services gains of discharging early with hs-cTnT.

“We’ve had high sensitivity troponin now for very close to a decade and it’s only now that we’ve started to think about how to effectively use it.

So the issues now aren’t about the test performance, its not about the innovation – it’s actually about how we as a health service use and systematise that information because poor use of innovation leads to poor outcomes at greater expense and limited benefit.

The findings are also published in Circulation.