What is the diagnosis and treatment approach for a patient presenting with symptoms suggestive of acute coronary syndrome, such as chest pain or shortness of breath, with consideration of their age, sex, past medical history, including any history of cardiovascular disease, hypertension, or diabetes?

ST Elevation Diagnosis

ECG Criteria for ST-Segment Elevation Myocardial Infarction

ST-segment elevation measured at the J point must be present in two contiguous leads to diagnose STEMI. 1

Specific Voltage Thresholds by Lead and Demographics

• In leads V2-V3:

  • Men <40 years: ≥0.25 mV (2.5 mm) 1
  • Men ≥40 years: ≥0.2 mV (2 mm) 1
  • Women (all ages): ≥0.15 mV (1.5 mm) 1

• In all other leads: ≥0.1 mV (1 mm) in the absence of left ventricular hypertrophy or left bundle branch block 1

ST-Elevation Equivalents Requiring Immediate Reperfusion

Several ECG patterns represent STEMI equivalents and mandate the same urgent treatment as classic ST elevation: 1

• Posterior MI: ST-segment depression in leads V1-V3 with positive terminal T-waves (ST-elevation equivalent), confirmed by concomitant ST elevation ≥0.1 mV in posterior leads V7-V9 1

• Right ventricular infarction: In inferior MI, record right precordial leads V3R and V4R to identify ST elevation indicating RV involvement 1

• New or presumably new left bundle branch block (LBBB): The ECG diagnosis is difficult but often possible if marked ST abnormalities are present; somewhat complex algorithms exist but clinical context is critical 1

Timing Requirements

The ST-segment elevation must be persistent for >20 minutes to distinguish STEMI from transient ischemia. 1 This duration reflects acute total or subtotal coronary occlusion requiring immediate reperfusion therapy. 1

ECG Acquisition Timeline

A 12-lead ECG must be obtained and interpreted within 10 minutes of arrival at any healthcare facility for all patients with acute chest pain. 1 This applies whether the patient presents to an emergency department, office setting, or chest pain unit. 1

Pre-Hospital ECG

If emergency medical services are involved, the ECG should ideally be obtained in the pre-hospital setting to expedite diagnosis and allow pre-activation of the catheterization laboratory. 1

Clinical Context Integration

High-Probability Clinical Features

The ECG findings must be interpreted alongside clinical presentation. Symptoms most consistent with acute MI include: 1

• Chest or left arm pain/discomfort as the chief symptom reproducing prior documented angina 1
• Known history of coronary artery disease including prior MI 1
• Symptoms lasting >20 minutes unrelieved by nitroglycerin 1

Associated Physical Examination Findings

High-risk examination findings that support STEMI diagnosis include: 1

• Transient mitral regurgitation murmur 1
• Hypotension 1
• Diaphoresis 1
• Pulmonary edema or rales 1

Atypical Presentations Requiring High Suspicion

Up to 30% of STEMI patients present with atypical symptoms, and these patients are at higher risk due to delayed diagnosis and treatment. 1

Women-Specific Considerations

Women presenting with chest pain are at risk for underdiagnosis, and potential cardiac causes must always be considered. 1 Obtain a history emphasizing accompanying symptoms more common in women with ACS, including: 1

• Shortness of breath 1
• Nausea 1
• Fatigue 1

Elderly Patients (≥75 years)

In patients ≥75 years with chest pain, consider ACS when accompanying symptoms include: 1

• Shortness of breath 1
• Syncope 1
• Acute delirium 1
• Unexplained fall 1

Other Atypical Presentations

Patients may present with anginal equivalents rather than chest pain: 1

• Isolated dyspnea 2
• Epigastric pain 1
• Pain in the left arm 1
• Palpitations 1

Diagnostic Pitfalls and Confounders

Conditions That Complicate ECG Interpretation

Several conditions make ST-elevation diagnosis more challenging but still require prompt management: 1

• Left bundle branch block: Use complex algorithms or rely heavily on clinical context; marked ST abnormalities support MI diagnosis 1
• Left ventricular hypertrophy: May cause baseline ST abnormalities 1
• Paced rhythm: Obscures native ST segments 1
• Early repolarization: Benign variant more common in young patients; distinguished by J-point notching and upward concavity 1
• Pericarditis: Causes diffuse ST elevation (not localized to vascular territory) with PR depression 1

Serial ECGs

If the initial ECG is non-diagnostic but clinical suspicion remains high, obtain serial ECGs every 15-30 minutes or with recurrent symptoms. 1 ST-segment changes may evolve over time, and dynamic changes strongly support acute ischemia. 1

Immediate Management Upon STEMI Diagnosis

Once STEMI is diagnosed on ECG, initiate the following within minutes: 1, 2

1. Activate the catheterization laboratory immediately for primary PCI with a door-to-balloon time goal of ≤120 minutes 2

2. If PCI cannot be achieved within 120 minutes, administer fibrinolytic therapy (alteplase, reteplase, or tenecteplase at full dose for patients <75 years; half dose for ≥75 years) 2

3. Initiate dual antiplatelet therapy: aspirin 162-325 mg chewed immediately plus a P2Y12 inhibitor (ticagrelor preferred) 3, 4

4. Begin parenteral anticoagulation with enoxaparin, fondaparinux, or unfractionated heparin 3

5. Continuous cardiac monitoring to detect life-threatening arrhythmias 1

Troponin Measurement in STEMI

While troponin elevation confirms myocardial necrosis, do not delay reperfusion therapy to wait for troponin results in patients with diagnostic ST elevation. 1 The ECG diagnosis alone is sufficient to proceed with immediate reperfusion. 1 Troponin should be measured as soon as possible but in parallel with, not instead of, urgent revascularization. 1