Case: A 57-year-old woman presents with left-sided chest pain that started 90 minutes ago. The pain radiates to her right arm, and she has nausea without vomiting. The pain began while she was doing some yard work. The initial electrocardiogram (ECG) is unremarkable.

Question: Can emergency physicians rule in or out an acute myocardial infarction (AMI) in one hour using a high-sensitivity troponin and ECG?

Background: About 5 percent of all patients presenting to the ED with acute chest pain will have a ST elevated myocardial infarction (STEMI).¹ This leaves the other 95 percent of chest pain patients. Our job in the ED is to figure out whom we will rule in versus rule out for AMI.

Many cardiac biomarkers have been used over the last 60 years to try to identify patients with AMI. A limitation of current troponin assays is that they can take three to four hours to rise. This means the diagnosis of non-STEMI can take many hours of continued monitoring with serial blood sampling.

High-sensitivity troponin assays are now being used in many emergency departments. They offer very high sensitivity but are less specific than prior troponin assays.

Relevant Article: Reichlin T, Twerenbold R, Wildi K, et al. Prospective validation of a 1-hour algorithm to rule-out and rule-in acute myocardial infarction using a high-sensitivity cardiac troponin T assay. CMAJ. 2015;187(8):E243-E252.

• Population: Patients presenting to the ED within 12 hours of onset of nontraumatic chest pain or symptoms suggestive of AMI.
• Intervention: High-sensitivity troponin T at time 0 and 1 hour with ECG
• Comparison: Two independent cardiologists.
• Outcome: AMI.

Authors’ Conclusions: “This rapid strategy incorporating high-sensitivity cardiac troponin T baseline values and absolute changes within the first hour substantially accelerated the management of suspected AMI by allowing safe rule-out as well as accurate rule-in of AMI in three out of four patients.”

Key Results: There were 1,320 patients who presented to the ED within 12 hours of onset of nontraumatic chest pain or other symptoms suggestive of AMI. AMI was the final diagnosis in 17 percent of those patients.

The researchers divided patients into three different categories: rule-out AMI (60 percent), rule-in AMI (16 percent), and observation zone (24 percent). The one-hour algorithm test characteristics for the 60 percent who were ruled out were:

• Area under the curve 0.96 (95 percent confidence interval [CI], 0.95–0.97)
• Sensitivity of 99.6 percent (95 percent CI, 97.6–99.9 percent) and specificity of 95.7 percent (95 percent CI, 94.3–96.8 percent)
• Negative predictive value 99.9 percent (95 percent CI, 99.3–100 percent) and positive predictive value 78.2 percent (95 percent CI, 72.1–83.6 percent)
• Positive likelihood ratio of 23 and negative likelihood ratio of 0.004

EBM Commentary: This was an attempt to investigate whether a one-hour algorithm can rule out and rule in acute myocardial infarction using a high-sensitivity troponin as a biomarker. There were a number of concerns with this manuscript.