Background: Chest pain is one of the most common symptoms in patients presenting to the emergency department (ED). Identifying the minority of patients with an acute coronary syndrome (ACS) is a challenge. The introduction of high-sensitivity cardiac troponin (hs-cTn T and I) assays has radically improved the assessment. The aim of this thesis was to evaluate four methods of assessing patients presenting with suspected ACS in the era of hs-cTn.Methods and results: In Study I, we retrospectively evaluated the value of predischarge exercise ECG testing in 951 chest pain patients in whom myocardial infarction (MI) had been ruled out by means of hs-cTnT. We found no significant differences regarding death or MI between patients with a positive or a negative test, neither at 90 (n=1 1.1% vs. n=1 0.2%), nor at 365 days (n=2 2.1% vs. n=4 0.7%) of follow-up. In total, there were 9 (0.9%) deaths and 10 (1.1%) MIs within 365 days. The one-year rates of death (1.3%) and MI (0.5%) in a matched Swedish population were comparable.Study II was a retrospective evaluation of the diagnostic sensitivity of an undetectable level of hs-cTnT at presentation, with and without information from the electrocardiogram (ECG), to rule out MI in a non-ST-segment elevation MI (NSTEMI) population presenting early. Twenty-four (2.6%) of the 911 early presenting NSTEMI patients initially had an undetectable level of hs-cTnT. In patients presenting >1–≤2 hours from symptom onset, the sensitivity for MI when combining hs-cTnT and ECG was 99.4% (95% confidence interval CI 98.4%–99.8%). In patients presenting =1 hour from symptom onset and in patients aged =65 years without prior MI, the sensitivity was insufficient. NSTEMI patients presenting with an undetectable level of hs-cTnT were younger but had a similar 30-day outcome to NSTEMI patients presenting with a detectable level of hs-cTnT.In Study III, we retrospectively evaluated a one-hour hs-cTnT algorithm in 1,091 chest pain patients with a non-elevated hs-cTnT when presenting to the ED and examined early dynamic changes in hs-cTnT. Dynamic one-hour changes (Δ ≥3 ng/L) occurred in 23 patients (2.1%). Fifteen patients (65.2%) in the dynamic group were admitted, compared to 148 patients (13.9%) in the non-dynamic group (p<0.001). Four of the patients admitted (26.7%) in the dynamic and one (0.7%) in the non-dynamic group were diagnosed with an MI (p<0.001). No death or MI occurred within 30 days among those discharged from the ED.In Study IV, we evaluated the clinical effects of implementing a one-hour hs-cTnT or I algorithm combined with the HEART score in a prospective observational before-after study including 1,233 patients at six centres. The new strategy was associated with a reduction in admission rate (59% to 33%, p<0.001, adjusted odds ratio 95% CI: 0.33 0.25–0.42), median time to discharge (23.2 to 4.7 hours, p<0.001) and median health care-related costs (€1,651 to €1,019, p<0.001). The rates of death and MI were very low.Conclusions: Rapid hs-cTn algorithms improve the prognostic assessment in patients with suspected ACS, making routine admission and predischarge exercise ECG testing redundant.