What are the diagnostic criteria and initial management for a suspected STEMI in a prehospital setting?

From the Guidelines

Rapid recognition and management of suspected ST-elevation myocardial infarction (STEMI) in the prehospital setting is crucial, and diagnostic criteria include chest pain or discomfort, ST-segment elevation of ≥1 mm in two or more contiguous leads on 12-lead ECG, or new left bundle branch block, as recommended by the 2017 ESC guidelines 1.

Diagnostic Criteria

The diagnostic criteria for STEMI include:

• Chest pain or discomfort lasting more than 20 minutes
• ST-segment elevation of ≥1 mm in two or more contiguous leads on 12-lead ECG
• New left bundle branch block
• ST-segment elevation (measured at the J-point) is considered suggestive of ongoing coronary artery acute occlusion in the following cases: at least two contiguous leads with ST-segment elevation 2.5 mm in men < 40 years, 2 mm in men 40 years, or 1.5 mm in women in leads V2 –V3 and/or 1 mm in the other leads [in the absence of left ventricular (LV) hypertrophy or left bundle branch block LBBB] 1

Initial Management

Initial management should focus on:

• Rapid assessment
• Oxygen administration if saturation is below 94%
• Establishing IV access
• Administering a medication regimen of aspirin 325 mg chewed, nitroglycerin 0.4 mg sublingually (if systolic BP >90 mmHg), and pain control with morphine 2-4 mg IV if needed
• Paramedics should immediately notify the receiving hospital of a suspected STEMI to activate the cardiac catheterization team and minimize door-to-balloon time, as recommended by the 2015 American Heart Association guidelines 1
• Continuous cardiac monitoring is essential, and some EMS systems may administer additional antiplatelet therapy such as P2Y12 inhibitors (clopidogrel 600 mg, ticagrelor 180 mg, or prasugrel 60 mg) based on local protocols

Transport to PCI-Capable Facility

Rapid transport to a PCI-capable facility is crucial, with a goal of first medical contact to device time under 90 minutes, as recommended by the 2015 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations 1 These interventions are critical because timely reperfusion therapy significantly reduces myocardial damage and improves survival rates in STEMI patients, with each 30-minute delay increasing mortality risk by approximately 7.5% 1

From the FDA Drug Label

DOSAGE & ADMINISTRATION Myocardial Infarction Early Treatment During the early phase of definite or suspected acute myocardial infarction, initiate treatment with metoprolol tartrate as soon as possible after the patient’s arrival in the hospital. In a large (1,395 patients randomized), double-blind, placebo-controlled clinical study, metoprolol was shown to reduce 3-month mortality by 36% in patients with suspected or definite myocardial infarction

The diagnostic criteria for a STEMI are not explicitly stated in the provided drug labels. However, the labels do mention the treatment of suspected or definite myocardial infarction. To confirm a STEMI in a prehospital setting, a 12-lead ECG is typically used to diagnose the condition, but this information is not provided in the drug labels. The initial management for a suspected STEMI in a prehospital setting may involve administering metoprolol tartrate as soon as possible after the patient's arrival in the hospital, but the prehospital administration is not explicitly mentioned in the labels 2 2. Key points to consider in the management of suspected STEMI include:

• Early treatment: Initiate treatment as soon as possible after the patient's arrival in the hospital.
• Monitoring: Monitor blood pressure, heart rate, and electrocardiogram during treatment.
• Dosage: The dosage of metoprolol tartrate for the treatment of suspected or definite myocardial infarction is not explicitly stated for prehospital use.

From the Research

Diagnostic Criteria for STEMI

To confirm a STEMI on a 12-lead prehospital ECG, the following diagnostic criteria should be considered:

• ST-segment elevation of at least 1 mm in two or more contiguous leads [ 3 ]
• The presence of Q waves or other signs of myocardial infarction may also be indicative of STEMI [ 4 ]
• It is essential to note that ECG evidence of STEMI can evolve over time, and serial ECGs may be necessary to detect STEMI [ 4,5 ]

Initial Management of Suspected STEMI

The initial management of suspected STEMI in a prehospital setting includes:

• Acquisition of a 12-lead ECG as soon as possible [ 3,4 ]
• Transmission of the ECG to the emergency department or a cardiac center for analysis [ 6 ]
• Activation of the cardiac catheterization laboratory prior to patient arrival at the hospital, if STEMI is confirmed [ 3 ]
• Administration of antithrombotic therapy, including antiplatelet and anticoagulant agents, as indicated [ 7 ]

Serial ECGs and Telemetry

Serial prehospital 12-lead ECGs can increase the identification of STEMI, particularly in patients with atypical symptoms [ 4,5 ]

• Telemetry-assisted prehospital ECG analysis can lead to earlier detection of STEMI and improve patient outcomes [ 6 ]
• The use of serial ECGs and telemetry can help identify patients with dynamic ST-segment changes, which may indicate STEMI [ 5 ]

Key Considerations

• Paramedics can accurately diagnose STEMI on a prehospital 12-lead ECG, with a high degree of sensitivity and specificity [ 3 ]
• A single prehospital ECG may not be sufficient to rule out STEMI, and serial ECGs may be necessary [ 4 ]
• The time required for transmission and analysis of the ECG can be minimal, allowing for rapid decision-making and treatment [ 6 ]