Is the MONA protocol still recommended for ACS?

The MONA acronym is outdated as a universal protocol. Aspirin is the only component given routinely. Oxygen is only for hypoxic patients. Nitrates are for active chest pain but are contraindicated in right ventricular infarction. Morphine is for persistent ischemic pain not relieved by nitrates.

Acute Coronary Syndrome (ACS) Guideline

Q: What is the difference between NSTEMI and Unstable Angina?

Both are types of NSTE-ACS. In NSTEMI, there is enough ischemia to cause myocyte death, resulting in elevated cardiac troponin levels. In Unstable Angina, the ischemia is not severe enough to cause detectable necrosis, so troponin levels remain normal.

Q: What is a P2Y12 inhibitor?

P2Y12 inhibitors are potent antiplatelet agents that block the P2Y12 receptor on platelets, preventing activation and aggregation. They are a cornerstone of dual antiplatelet therapy in ACS. Examples include clopidogrel, prasugrel, and ticagrelor.

Q: Why is a central line not required for vasopressors in ACS initially?

While central access is ideal for sustained vasopressor infusions, initiating pressors via a well-sited peripheral IV in a proximal vein is acceptable in an emergency to rapidly restore perfusion while central access is being obtained.

Q: Can this ACS guideline be used for patients with a left bundle branch block?

A new or presumed-new LBBB in the context of ischemic symptoms is considered a STEMI equivalent and should trigger immediate reperfusion protocols. The STEMI pathway applies in that situation.

1. Initial 12-Lead EKG Findings

2. High-Sensitivity Cardiac Troponin Result

Diagnosis & Initial Management Plan

Clinical Pathway Summary

Recent Updates

Routine upstream P2Y12 pretreatment is no longer recommended in NSTE-ACS when early angiography is planned and the coronary anatomy is unknown — load at or after catheterization. Pretreatment with clopidogrel or ticagrelor may be considered only if angiography is expected to be delayed beyond 24 hours; prasugrel should not be used for pretreatment. STEMI patients are still loaded at diagnosis.
Ticagrelor or prasugrel are preferred over clopidogrel for ACS managed with PCI; default dual antiplatelet therapy (DAPT) is at least 12 months unless the patient is at high bleeding risk.
Earlier, more aggressive lipid lowering: high-intensity statin for all, with early addition of ezetimibe ± a PCSK9 inhibitor when LDL-C remains ≥70 mg/dL (recheck at 4–8 weeks).
Complete revascularization is now recommended for STEMI with multivessel disease, and radial access is the preferred default approach.

Source: Rao SV, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes. Circulation 2025;151(13):e771–e862. PMID: 40014670.

Key Knowledge Points

This Acute Coronary Syndrome Guideline pathway helps standardize initial assessment and management based on EKG and troponin findings.
For STEMI, the immediate goal is reperfusion. “Time is muscle,” and the system goal is a first medical contact-to-device time of ≤90 minutes for PCI. Complete revascularization of significant non-culprit lesions and radial access are preferred.
For NSTE-ACS (NSTEMI/Unstable Angina), initial management involves anti-ischemic therapy, antiplatelet agents, anticoagulation, and risk stratification (e.g., using GRACE or TIMI scores) to guide timing of angiography.
Antiplatelet strategy: aspirin plus an oral P2Y12 inhibitor is the backbone — but routine P2Y12 pretreatment is not recommended in NSTE-ACS when anatomy is unknown and early angiography is planned (load at/after cath). Ticagrelor or prasugrel are preferred over clopidogrel for PCI.
Nitrates and morphine are used for symptom relief but do not improve mortality; morphine can delay the absorption and onset of oral P2Y12 inhibitors, so reserve it for refractory ischemic pain.
Oxygen should only be administered if the patient’s oxygen saturation is <90%, as hyperoxia may be harmful.
Lipid management: begin a high-intensity statin early in all ACS patients and add ezetimibe ± a PCSK9 inhibitor when LDL-C remains ≥70 mg/dL.

About This ACS Guideline Tool

This interactive Acute Coronary Syndrome (ACS) Guideline tool is designed for healthcare professionals to rapidly navigate the diagnostic and initial therapeutic pathway for patients presenting with suspected ACS. By inputting key initial findings—specifically from the 12-lead EKG and high-sensitivity cardiac troponin assays—the tool provides a clear diagnosis (STEMI, NSTEMI, or Unstable Angina) and outlines the immediate, evidence-based management steps recommended by major cardiology guidelines.

Navigating the Diagnostic Pathway

The diagnosis of Acute Coronary Syndrome is a time-critical process that hinges on two key initial investigations:

12-Lead EKG: The EKG is the most important initial diagnostic test. It rapidly identifies patients with ST-segment elevation myocardial infarction (STEMI) who require immediate reperfusion therapy. It can also suggest NSTE-ACS through findings like ST-segment depression or T-wave inversions.
Cardiac Troponins: High-sensitivity cardiac troponins (hs-cTn) are the preferred biomarkers for detecting myocardial necrosis. A rise and/or fall in troponin levels above the 99th percentile upper reference limit is the hallmark of an acute myocardial infarction (MI).

Clinical Interpretation & Management Details

ST-Elevation Myocardial Infarction (STEMI)

A diagnosis of STEMI is a medical emergency. The primary goal is immediate and complete reperfusion of the occluded coronary artery.

Reperfusion: Primary Percutaneous Coronary Intervention (PCI) is the preferred strategy if it can be performed within 120 minutes of first medical contact. If not, fibrinolytic therapy should be considered.
Medical Therapy: Initial treatment includes Aspirin, a P2Y12 inhibitor (e.g., ticagrelor or prasugrel), and parenteral anticoagulation (e.g., heparin).

Non-ST-Elevation ACS (NSTEMI & Unstable Angina)

Patients without ST-segment elevation are initially managed with anti-ischemic and antithrombotic therapies, followed by risk stratification to determine the timing of angiography.

Antiplatelet & Anticoagulation: Aspirin plus an oral P2Y12 inhibitor and parenteral anticoagulation. In NSTE-ACS planned for an early invasive strategy with unknown anatomy, the P2Y12 inhibitor is generally loaded at or after angiography rather than empirically in the ED (routine pretreatment is not recommended; it may be considered only if angiography is delayed beyond 24 hours, and prasugrel is not used for pretreatment).
Risk Stratification: Tools like the GRACE or TIMI risk score are used. High-risk patients benefit from an early invasive strategy (angiography within 24 hours), while lower-risk patients may be managed with a more conservative approach.

Key Antithrombotic Dosing & Cautions

Aspirin: 162–325 mg non–enteric-coated, chewed, as soon as ACS is suspected.
P2Y12 inhibitor (load per timing above): ticagrelor 180 mg; prasugrel 60 mg (avoid for pretreatment; contraindicated with prior stroke/TIA; use caution or avoid if ≥75 years or <60 kg); clopidogrel 300–600 mg when potent agents are contraindicated, unavailable, or oral anticoagulation is needed.
Unfractionated heparin: ~60 units/kg IV bolus (max ≈4,000 units) followed by a 12 units/kg/hr infusion (max ≈1,000 units/hr), titrated to aPTT/anti-Xa; when a GP IIb/IIIa inhibitor is used the bolus is 50–70 units/kg. Enoxaparin is an alternative.
Cautions: morphine delays oral P2Y12 absorption (reserve for refractory pain); nitrates are contraindicated in RV infarction, severe aortic stenosis, and recent PDE5-inhibitor use (sildenafil <24h, tadalafil <48h); in cardiogenic shock, culprit-lesion-only PCI is preferred over routine immediate multivessel PCI.

Limitations

This tool provides initial guidance based on a simplified algorithm. It does not replace comprehensive clinical evaluation and judgment. The management of ACS is complex and must account for patient-specific factors, contraindications, and institutional resources. This Acute Coronary Syndrome guideline tool is for educational and informational purposes only.

Frequently Asked Questions (FAQ)

1. What is the difference between NSTEMI and Unstable Angina?

Both are types of NSTE-ACS. The key difference is the presence of myocardial necrosis. In NSTEMI, there is enough ischemia to cause myocyte death, resulting in elevated cardiac troponin levels. In Unstable Angina, the ischemia is not severe enough to cause detectable necrosis, so troponin levels remain normal.

2. Is the MONA protocol (Morphine, Oxygen, Nitrates, Aspirin) still recommended?

The “MONA” acronym is outdated as a universal protocol. Aspirin is the only component given routinely. Oxygen is only for hypoxic patients (SpO₂ < 90%). Nitrates are for active chest pain but are contraindicated in right ventricular infarction or severe aortic stenosis. Morphine is a reasonable choice for persistent ischemic chest pain not relieved by nitrates.

3. What is a “P2Y12 inhibitor”?

P2Y12 inhibitors are a class of potent antiplatelet agents that block the P2Y12 receptor on platelets, preventing their activation and aggregation. They are a cornerstone of DAPT in ACS. Examples include clopidogrel, prasugrel, and ticagrelor.

4. Why is a central line not required for vasopressors in ACS initially?

While central access is ideal for sustained vasopressor infusions, initiating pressors like norepinephrine via a well-sited, large-bore peripheral IV in a proximal vein (e.g., antecubital fossa) is acceptable in an emergency to rapidly restore perfusion while central access is being obtained. This is a crucial temporizing measure.

5. Can this Acute Coronary Syndrome guideline be used for patients with a left bundle branch block (LBBB)?

A new or presumed-new LBBB in the context of ischemic symptoms is considered a “STEMI equivalent” and should trigger immediate reperfusion protocols. This tool’s “STEMI” pathway applies in that situation.

Related Calculators

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⚠️ Disclaimer:

This tool is for informational and educational purposes only and is not a substitute for professional clinical judgment. All treatment decisions must be made by a qualified healthcare professional considering the individual patient’s full clinical context.

❤️ ACS Guideline & Clinical Pathway