Evaluation of the safety of the ESC 2011 guidelines for rapid rule-out of NSTEMI using sensitive cardiac troponin I ultra

Abstract

Purpose: Sensitivity cardiac troponin (s-cTn) assays have been shown to improve the early diagnosis of acute myocardial infarction. The 2011 ESC guidelines for the management of acute coronary syndromes in patients without persistent ST-segment elevation contain for the first time a new fast track rule-out protocol including high-sensitivity troponin. There is a lack of empirical data about the safety of the protocol using sensitive troponins. We intended to verify the safety of this fast track protocol in our prospective study setting. Methods: Out of our ongoing international multicenter study 1922 consecutive patients who presented with symptoms suggestive of acute myocardial infarction and absence of significant ST-elevations in the ECG were included. The final diagnosis was adjudicated by two independent cardiologists using all available information including high-sensitivity cardiac troponin T. The ESC rapid rule-out protocol was tested using the sensitive cTnI-Ultra (s-cTnI, 99th percentile defined as 0.04 μg/l) performed on blood samples obtained in the emergency department at presentation and after 3 hours according to the current guidelines. All patients were divided in line with the ESC algorithm into the subgroups of late presenters with chest pain onset/maximum (CPM) ≥ 6 hours and early presenters with CPM < 6 hours. In the former group, rapid rule-out was based on a single mesurement using s-cTnI and in the latter group, on two s-cTnI values, at presentation and at 3 hours. Results: NSTEMI was the final diagnosis in 18%. There were 79% (n=1524) having a s-cTnI below the cutoff at presentation. The ESC protocol allowed the rule-out of NSTEMI at presentation in 25% of the total group and after 3 hours in additional 20%. Using only the s-cTnI criteria, the protocol correctly ruled-out 96.5% (95% Confidence Interval (CI) 94.3 to 97.9%) of applicable patients at presentation and 98.6% (95% CI 95.0 to 98.6%). Adding clinical criteria (pain assessment, GRACE Score, exclusion of differential diagnoses) the protocol correctly ruled-out 99.0% (95% CI 97.5 to 99.6%) at presentation and 99.2% (95% CI 97.5 to 99.8%) after 3 hours. Pain assessment and differential diagnoses were the key additional criteria. Conclusions: Using a sensitive assay for troponin I, the 2011 ESC guidelines provide an effective way of rapid rule-out of NSTEMI with a very high however not perfect rule-out.