41 A Baseline and 30-Minute Algorithm for Rapid Rule-Out of Acute Myocardial Infarction: Does it Get Any Better Than This?

Abstract

Approximately 20 million individuals present to the emergency department (ED) with symptoms suggestive of acute myocardial infarction (AMI) in the United States (US) and Europe annually. A baseline and 1-hour rule-in/rule-out AMI algorithm using high sensitivity cardiac troponin T (hs-cTnT) measurements is recommended for use in the 2015 European Society of Cardiology (ESC) NSTEMI guidelines. Given the early release and rapid accumulation of hs-cTnT during AMI it may be possible that a shorter time period could be utilized for the rule-out zone of this algorithm. The purpose of this study was to determine if baseline and 30-minute hs-cTnT levels in patients presenting to a US ED population with suspected acute coronary syndrome (ACS) could accurately rule out AMI in a significant number of these individuals. Patients presenting with symptoms suspicious of ACS as determined by the emergency physician at a single US tertiary care urban center were enrolled in this study. Study baseline (within 60 minutes of triage electrocardiogram) and 30 minute (± 10 minutes) blood samples were obtained. AMI diagnosis was independently adjudicated by a cardiologist and emergency physician using the 3rd universal definition, the hospital troponin I assay (Siemens Ultra, 99th percentile 40 mg/L) and all data available 30 days post discharge. The hs-cTnT assay studied was the Roche Diagnostics Elecsys 2010 (99th percentile 14 ng/L) and measurements were independently done at the University of Maryland. Of the 569 studied subjects 44 (7.7 %) had an adjudicated AMI diagnosis. The baseline and 30 minute hs-cTnT measurements were available in 539 patients. Analysis of the hs-cTnT values so as to miss no AMI required a baseline level < 8 and a delta value at 30 minutes < 3 ng/L (sensitivity 100%, negative predictive value 100%) and was seen in 221 or 41.0% of subjects (leaving 318 or 59.0% needing further AMI workup). Enrolled patients had many cardiac risk factors (hypertension 74.4%, diabetes 23.7%, hypercholesterolemia 43.3%, known coronary artery disease [CAD] 30.1%, revascularization 19.2%, myocardial infarction 24.0%, congestive heart failure 12.8% and family history of CAD 33.7%) and their overall HEART scores were in the lower range (median 3, interquartile ranges 2-4). Additionally no dialysis patient (30) could be ruled out using these times and cut points. A baseline and 30-minute hs-cTnT algorithm using cut points that are all below the 99th percentile may very accurately rule out AMI in over 40% of patients being evaluated for suspected ACS in a US ED population with significant cardiac risk factors. It is possible that there may be alternative better ways (draw timings, cut points) in the US for the rule-in/rule-out of AMI. Larger clinical US trials are needed to verify our rule-out results before routine clinical application.