The 2015 Guidelines Update marks a change in the scope of the AHA guidelines for the evaluation and management of ACS. Starting with this update, recommendations will be limited to the prehospital and emergency department phases of care. In-hospital care is addressed by guidelines for the management of myocardial infarction published jointly by the AHA and the American College of Cardiology Foundation.

Summary of Key Issues and Major Changes

Key issues with major changes in the 2015 Guidelines Update recommendations for ACS include the following:

  • Prehospital ECG acquisition and interpretation
  • Choosing a reperfusion strategy when prehospital fibrinolysis is
  • Choosing a reperfusion strategy at a non–PCI-capable hospital
  • Troponin to identify patients who can be safely discharged from the
    emergency department
  • Interventions that may or may not be of benefit if given before
    hospital arrival

Prehospital ECG Acquisition and Interpretation

2015 (New): Prehospital 12-lead ECG should be acquired early for patients with possible ACS.

2015 (New): Trained nonphysicians may perform ECG interpretation to determine whether or not the tracing shows evidence of STEMI.

2015 (Updated): Computer-assisted ECG interpretation may be used in conjunction with interpretation by a physician or trained provider to recognize STEMI.

2015 (Updated): Prehospital notification of the receiving hospital and/or prehospital activation of the catheterization laboratory should occur for all patients with a STEMI identified on prehospital ECG.

2010 (Old): If providers are not trained to interpret the 12-lead ECG, field transmission of the ECG or a computer report to the receiving hospital was recommended.

2010 (Old): Advance notification should be provided to the receiving hospital for patients identified as having STEMI.

Why: A 12-lead ECG is inexpensive, is easy to perform, and can rapidly provide evidence of acute ST elevation. Concern that nonphysician interpretation of ECGs could lead to either overdiagnosis with a resulting overuse of resources or, alternately, underdiagnosis, which could result in a delay to treatment, has inhibited expansion of ECG programs to EMS systems. Similar concerns existed with computer interpretation of ECGs. A review of the literature shows that when fibrinolysis is not given in the prehospital setting, early hospital notification of the impending arrival of a patient with ST elevation or prehospital activation of the catheterization laboratory reduces time to reperfusion and reduces morbidity and mortality. Because it may take time for the inexperienced provider to develop skill with 12-lead ECG interpretation, computer interpretation can be expected to increase the accuracy of interpretation when used in conjunction with trained nonphysician interpretation.


2015 (New): Where prehospital fibrinolysis is available as part of the STEMI system of care and direct transport to a PCI center is available, prehospital triage and transport directly to a PCI center may be preferred because it results in a small relative decrease in the incidence of intracranial hemorrhage. There is, however, no evidence of mortality benefit of one therapy over the other.

2015 (New): In adult patients presenting with STEMI in the emergency department of a non–PCI-capable hospital, we recommend immediate transfer without fibrinolysis from the initial facility to a PCI center, instead of immediate fibrinolysis at the initial hospital with transfer only for ischemia-driven PCI.

2015 (New): When STEMI patients cannot be transferred to a PCI-capable hospital in a timely manner, fibrinolytic therapy with routine transfer for angiography (see below) may be an acceptable alternative to immediate transfer to primary PCI.

2015 (New): When fibrinolytic therapy is administered to a STEMI patient in a non–PCI-capable hospital, it may be reasonable to transport all postfibrinolysis patients for early routine angiography in the first 3 to 6 hours and up to 24 hours rather than transport postfibrinolysis patients only when they require ischemia-guided angiography.

2010 (Old): Transfer of high-risk patients who have received primary reperfusion with fibrinolytic therapy is reasonable.

Why: Fibrinolysis has been the standard of care for STEMI for more than 30 years. In the past 15 years, PPCI has become more readily available in most parts of North America and has been shown to modestly improve outcomes, compared with fibrinolysis, when PPCI can be provided in a timely manner by experienced practitioners. However, when there is a delay to PPCI, depending on the length of that delay, immediate fibrinolysis may overcome any additional benefits of PCI. Direct transfer to a PCI-capable hospital compared with prehospital fibrinolysis does not produce any difference in mortality, but transfer for PPCI does result in a small relative decrease in the incidence of intracranial hemorrhage. A fresh look at the evidence has allowed stratification of treatment recommendations according to time from symptom onset and anticipated delay to PPCI, and has enabled recommendations specifically for clinicians at non–PCI-capable hospitals. Immediate PCI after treating with fibrinolysis provides no added benefit, but routine angiography within the first 24 hours after giving fibrinolysis does reduce the incidence of reinfarction.

Troponin to Identify Patients Who Can Be Safely Discharged From the Emergency Department

2015 (New): High-sensitivity troponin T and troponin I alone measured at 0 and 2 hours (without performing clinical risk stratification) should not be used to exclude the diagnosis of ACS, but high-sensitivity troponin I measurements that are less than the 99th percentile, measured at 0 and 2 hours, may be used together with low-risk stratification (Thrombolysis in Myocardial Infarction [TIMI] score of 0 or 1, or low risk per Vancouver rule) to predict a less than 1% chance of 30-day major adverse cardiac event (MACE). Also, negative troponin I or troponin T measurements at 0 and between 3 and 6 hours may be used together with very low-risk stratification (TIMI score of 0, low risk score per Vancouver rule, North American Chest Pain score of 0 and age less than 50 years, or low-risk HEART score) to predict a less than 1% chance of 30-day MACE.

2010 (Old): If biomarkers are initially negative within 6 hours of symptom onset, it was recommended that biomarkers should be remeasured between 6 to 12 hours after
symptom onset.

Why: Relying on a negative troponin test result, either alone or in combination with unstructured risk assessment, results in an unacceptably high rate of MACE at 30 days. However, predictions based on negative troponin test results, combined with structured risk assessment, carry a risk of less than 1% of MACE at 30 days.

Other Interventions

When a medication reduces morbidity or mortality, prehospital compared with hospital administration of that medication allows the drug to begin its work sooner and may further decrease morbidity or mortality. However, when urban EMS response and transport times are short, the opportunity for beneficial drug effect may not be great. Moreover, adding medications increases the complexity of prehospital care, which may in turn produce negative effects.

  • Adenosine diphosphate inhibition for hospital patients with suspected STEMI has been recommended for many years. Administration of an adenosine diphosphate inhibitor in the prehospital setting provides neither additional benefit nor harm compared with waiting to administer it in the hospital.
  • Unfractionated heparin (UFH) administered to patients with STEMI in the prehospital setting has not been shown to provide additional benefits to giving it in the hospital. In systems where prehospital administration of UFH already occurs, it is reasonable to continue to use it. Where it is not already used in the prehospital setting, it is just as reasonable to wait to give UFH until hospital arrival.
  • Before the 2010 recommendations, oxygen was routinely administered to all patients with suspected ACS regardless of oxygen saturation or respiratory condition. In 2010, weak evidence of no benefit and possible harm prompted a recommendation that supplementary oxygen was not needed for patients with ACS who had an oxyhemoglobin saturation of 94% or greater (i.e., no hypoxemia) and no evidence of respiratory distress. Further evidence that the routine administration of supplementary oxygen may be harmful, supported by a multicenter randomized controlled trial published since the 2015 systematic review,1 strengthens the recommendation that oxygen be withheld from patients with possible ACS who have a normal oxygen saturation (ie, who are without hypoxemia).
  • For STEMI patients, prehospital administration of UFH or bivalirudin is reasonable.
  • For suspected STEMI patients who are being transferred for PPCI, enoxaparin is a reasonable alternative to UFH.

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  1. Stub D, Smith K, Bernard S, et al. Air versus oxygen in ST-segment-elevation myocardial infarction. Circulation. 2015;131(24):2143-2150.
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