High-sensitivity troponin identified more myocardial infarctions, didn't affect mortality

The study's authors expected the introduction of a high-sensitivity assay to improve outcomes, so the results raise questions about the appropriate diagnostic threshold for myocardial infarction.

Switching from a contemporary cardiac troponin I assay to a high-sensitivity one for patients with suspected acute coronary syndrome did not reduce myocardial infarction or cardiovascular mortality during follow-up, a recent study found.

The cluster-randomized controlled trial included consecutive patients treated for suspected acute coronary syndrome in the EDs of 10 hospitals in Scotland between June 10, 2013, and March 3, 2016. Both the high-sensitivity cardiac troponin I assay with a sex-specific 99th percentile diagnostic threshold and a contemporary cardiac troponin I assay were run on all patients. During the trial's validation phase of six to 12 months, the high-sensitivity results were concealed from the attending clinician. At six months, five of the hospitals had the high-sensitivity test introduced, while the other five implemented it six months after that. The primary outcome was subsequent myocardial infarction or death from cardiovascular causes within a year of initial presentation. Results were published by The Lancet on Aug. 28.

Of the 48,282 patients included in the study (median age, 61 years; 47% women), 21% had troponin concentrations greater than the 99th percentile of the normal range of values, identified by the contemporary assay or the high-sensitivity assay. The high-sensitivity assay reclassified 17% (1,771 of 10,360) of patients with myocardial injury or infarction who were not identified by the contemporary assay. In those reclassified, subsequent myocardial infarction or cardiovascular death within a year occurred in 15% of the 720 patients treated in the validation phase and 12% of the 1,051 patients treated in the implementation phase (adjusted odds ratio for implementation vs. validation phase, 1.10; 95% CI, 0.75 to 1.61; P=0.620).

The study authors said they had expected the introduction of a high-sensitivity assay to improve outcomes, so the results of this study raise questions about whether the diagnostic threshold for myocardial infarction should be based on the 99th percentile derived from a normal reference population. They noted that only a third of the patients who were reclassified under the high-sensitivity assay had a diagnosis of type 1 myocardial infarction and would therefore benefit from evidence-based therapies. In addition, many of the patients who were reclassified had already been diagnosed with ischemic heart disease and treated accordingly. Most of those reclassified were also women, due to the sex-specific threshold, the authors noted.

The study did find a reduction in length of stay among the overall patient population with use of the high-sensitivity assay; the authors said “implementation might have improved the treating clinician's confidence that myocardial infarction had been ruled out, resulting in an earlier discharge.” They called for additional research on how “changing criteria for the classification of patients with myocardial injury and infarction will affect patient management and clinical outcomes,” and noted that the recommendation to use the 99th percentile from a healthy reference population is based only on expert consensus and observational studies.