Background: High sensitivity cardiac troponin I (hs-cTnI) assays are being approved for use in the United States (US). Our objective was to determine the efficacy of a 2 hour acute myocardial infarction (AMI) rule-out/rule-in European derived hs-cTnI algorithm when applied to patients in the US when the second sample was drawn 2-3 hours later in the High Sensitivity Cardiac Troponin I in the US (HIGH-US) study.
Methods: Adults presenting with any suspicion for AMI were included. Patients with STEMI were excluded. Baseline and 2-3 hour plasma samples were analyzed in a core laboratory (University of Maryland) using the Siemens Atellica hs-cTnI assay (99th % 45.0 ng/L). AMI was independently adjudicated using all 30 day clinical materials available.
Results: 2505 patients were enrolled with 1916 having complete data for the 2-3 hour algorithm analyses. Subjects had a mean age of 56.7 ± 12.9 years and 1419 (56.5%) were males Past medical history included hypertension in 1730 (69.1%), coronary artery disease, cardiac bypass surgery, percutaneous coronary interventions or AMI in 930 (37.1%) and diabetes in 739 (29.5%) while 83 (3.3%) were receiving renal dialysis. ECG abnormalities included ST depression (≥ 0.5) or elevation (> 1.0) in 231 (9.2%) or T wave inversions in 298 (11.9%). Patients with AMI (except on dialysis) had significantly more (p < 0.001) of each of these characteristics but they were also commonly seen in those without AMI. 1066 (55.6%) were ruled-out with a NPV 99.8% and sensitivity 99.1% (95%CI: 99.3-99.9 and 96.8-99.8 respectively). Of these 612 (31.9%) had a baseline hs-cTnI < 3 ng/L and 454 (23.7%) had a baseline hs-cTnI < 6 ng/L and a 1 hour delta value < 3 ng/L. 254(13.3%) were ruled-in with a PPV 69.7% and specificity 95.5% (95%CI: 63.8 -75.0 and 94.4-96.3 respectively). Of these 199 (10.4%) had a baseline hs-cTnI ≥ 120 ng/L and 55 (2.9%) had a delta value ≥ 12 ng/L. The remaining 596 (31.1%) in the continue evaluation zone had an adjudicated AMI prevalence of 7.0% (95%CI 5.3-9.4).
Conclusion: The European utilized 2 hour rule-out/rule-in algorithm using hs-cTnI for AMI evaluation yields very similar results (very high NPV) when used in an all comers US population with many cardiac risk factors when the second blood draw is 2-3 hours later. Further studies are needed to improve the PPV and specificity of a 2-3 hour rule-in algorithm for AMI in the US ED population.