1. In this prospective cohort study, a low serum troponin concentration under 5ng/L had a negative predictive value of 99.6% for the primary outcome of index myocardial infarction (MI).
2. At 1 year, patients with serum troponin concentrations of less than 5ng/L were at a lower risk of MI and cardiac death than those with troponin concentrations of 5ng/L or more.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Identifying patients at very low risk of heart attack who present with chest pain could reduce the number of unnecessary admissions. This prospective cohort study assessed the negative predictive value of high-sensitivity cardiac troponin-I assays for index MI, with the aim of identifying low risk patients that could be safely discharged. In patients without heart attack at presentation, a troponin concentration less than 5ng/L was found to have a high negative predictive value of greater than 99% for index MI in both derivation and validation cohorts. The results of this study are strong, as they are generalizable to the general population. A potential weakness of this study is that the results have not yet been tested in routine clinical practice. If further validated in clinical practice, high-sensitivity cardiac troponin-I assays could potentially decrease unnecessary or low risk cardiac admissions by up to two-thirds and achieve significant cost-savings for health care systems.
The study was funded by British Heart Foundation and Chief Scientist Office (Scotland).
In-Depth [prospective cohort]: This prospective cohort study aimed to define a threshold using high-sensitivity cardiac troponin-I assay that identifies patients with suspected acute coronary syndrome who are at low risk of MI and would potentially be suitable for discharge. The primary outcome was a composite index type I MI, or type 1 MI of cardiac death at 30 days. Secondary outcome was 1-year survival from MI or cardiac death following index presentation.
In the derivation cohort, 782 or the 4,870 patients (16%) had index MI, with 32 (1%) re-presenting with MI, and 75 (2%) cardiac deaths at 30 days. Troponin concentrations in patients without MI at presentation were less than 5ng/L in 2,311 (61%) of 3,799 patients with a negative predictive value of 99.6% (95% CI 99.3-99.8) for the primary outcome. Troponin concentrations were less than 5ng/L in 594 (56%) of 1,061 patients in two independent validation cohorts and had a negative predictive value of 99.4% (95% CI 98.8-99.1). These patients had a lower risk of MI at 1 year than did patients with troponin concentrations of 5ng/L or more (0.6% vs 3.3%; adjusted hazard ratio 0.41, 95% CI 0.21-0.80; p<0.0001).
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