Among patients with suspected acute coronary syndrome (ACS), the use of a high-sensitivity troponin assay protocol integrated into early emergency department work-up, was associated with a reduction in functional stress testing and an increase in coronary angiography and revascularisation—but the strategy did not improve patient outcomes ovre one year follow-up.
These were among the findings of RAPID-TnT, presented by Derek Chew, professor of cardiology at Flinders University (Adelaide, Australia), during a late-breaking trial session at the American College of Cardiology’s 70th Annual Scientific Session (ACC.21, 15–17 May, virtual).
RAPID-TnT sought to assess the impact of the superior reporting precision of high-sensitivity cardiac troponin T (hs-cTnT) assays when incorporated into a rapid protocol in terms of all-cause death or myocardial infarction. Chew told ACC.21 attendees that the subset of patients within initial modest elevations in troponin and receiving the hs-cTnT protocol were more likely to have a heart attack or to die during the one-year follow-up period compared with patients whose treatment was informed by the results of conventional blood testing procedures.
“We wanted to know whether giving physicians greater information about troponin concentrations within a zero/one-hour repeat-testing protocol would change how they managed patients and whether such changes would lead to improvements in outcomes,” said Chew, the principal investigator of the study. “We found that using high-sensitivity troponin in a rapid repeat-testing protocol, with recommendations for subsequent patient management, may have changed how physicians managed patients, but this did not lead to better outcomes.”
The randomised clinical trial used an assay that can detect levels of troponin T as low as five nanograms per litre (ng/L). By contrast, older, less-sensitive troponin tests could only accurately quantify troponin levels at around 40ng/L. With the new assay deployed, troponin results <29ng/L remained masked in routine clinical practice to enable robust evaluation of the impact of high sensitivity reporting care. Few randomised controlled trials have looked at whether using the newer, more-sensitive troponin tests leads to better outcomes for patients, Chew said.
The study involved 3,378 patients (median age 59 years, 53% male) who visited emergency rooms at four metropolitan centres across South Australia with chest pain or other symptoms of a possible heart attack. Patients were eligible for the study if the results of their initial electrocardiogram did not show clear signs that they were experiencing inadequate blood supply to the heart.
The participants were randomly assigned to one of two groups. Participants in the standard-care group received a troponin test on arrival at the emergency department and a second test three hours later. Treating physicians remained blinded to the test results below 29ng/L, in accordance with standards of practice at the time, and subsequent care was at the treating physician’s discretion.
In the intervention group, participants also received a troponin test on arrival at the emergency department, but they received a second test sooner—just one hour after the first. The results provided to physicians were unblinded, allowing them to see the troponin result down to a level of 5ng/L.
Based on the initial high-sensitivity troponin test result and the change in the troponin level over one hour, participants were categorised as “rule out,” “rule in” or “further observation” for a myocardial infarction, with guidance for subsequent care provided based on their category. The study’s primary endpoint was time to MI or death from any cause during the 12-month follow-up period.
Follow-up data were available for 3,270 participants (108 withdrew from the study by 12 months). For 92% of participants, both initial troponin T tests showed levels below 29 ng/L. Patients in the intervention group were discharged earlier than those in the standard-care group and underwent fewer stress tests and slightly more angiograms.
Overall, the researchers found no statistically significant differences in the number of MIs or deaths between the two groups during the 12-month follow-up period. However, in the subset of patients whose initial troponin levels were below 29ng/L, 3.7% of those in the intervention group had MI or died within the follow-up period, compared with 2.3% in the standard-care group. This difference amounted to a 60% increase in the risk of a MI or death for this subset of patients.
“This finding may imply that the practice changes observed with the use of a zero/one-hour, high sensitivity troponin T testing protocol—fewer stress tests and slightly more angiograms—may be associated with an increase in the risk of death or a heart attack within 12 months,” Chew said. “However, it is possible that this finding occurred by chance, and therefore it should be interpreted with caution. Overall, the finding may signal the continued utility of functional testing, such as stress tests, and a need for reconsideration of downstream investigations and therapies in the large population presenting with low-level troponin elevations.”
Findings of the study were also published in the journal Circulation.