What is the appropriate management for an adult patient with no specified medical history presenting with shortness of breath and chest pain, potentially indicating myocardial infarction (MI) or pulmonary embolism (PE)?

Management of Acute Shortness of Breath and Chest Pain

Immediately obtain a 12-lead ECG within 10 minutes of presentation and draw cardiac troponin to distinguish ST-elevation myocardial infarction (STEMI) from non-ST-elevation acute coronary syndrome (NSTEMI/unstable angina) or pulmonary embolism, while simultaneously initiating oxygen therapy and pain relief. 1

Immediate Actions Upon Presentation

First 10 Minutes: Simultaneous Assessment and Stabilization

ECG and Vital Signs:

• Record 12-lead ECG within 10 minutes to detect ST-segment elevations ≥1 mm in contiguous leads or new left bundle-branch block indicating STEMI 1
• Initiate continuous ECG monitoring immediately to detect life-threatening arrhythmias 1
• Measure oxygen saturation, blood pressure, heart rate, and respiratory rate 1

Laboratory Testing:

• Draw cardiac troponin (troponin I or T) immediately, with repeat measurement at 1-2 hours using rapid rule-in/rule-out algorithms 1
• Do not wait for troponin results before initiating reperfusion therapy if STEMI is identified on ECG 1
• Obtain complete blood count (hemoglobin/hematocrit) to screen for anemia as a secondary cause of ischemia 1

Immediate Symptom Relief:

• Administer morphine 4-8 mg intravenously with additional 2 mg doses every 5 minutes until pain relief, as pain causes sympathetic activation and increases cardiac workload 1
• Give oxygen 2-4 liters/minute by mask or nasal prongs, especially if breathless, hypoxic, or showing features of heart failure or shock 1
• Administer sublingual nitroglycerin 0.4 mg every 5 minutes up to 3 doses if systolic blood pressure >90 mmHg 2
• Give aspirin 162-325 mg (chewed) immediately unless contraindicated 1

Risk Stratification Based on ECG Findings

If STEMI Pattern Present (ST-elevation ≥1 mm in contiguous leads or new LBBB):

Immediate Reperfusion Decision:

• Activate catheterization laboratory for primary percutaneous coronary intervention (PCI) as the preferred reperfusion strategy 1
• Initiate unfractionated heparin with weight-adjusted bolus (5,000 units IV bolus followed by continuous infusion of 20,000-40,000 units/24 hours) without waiting for imaging confirmation 1, 3
• Consider alternative diagnoses if clinical presentation doesn't fit typical MI pattern, particularly massive pulmonary embolism which can mimic STEMI with ST-elevation in leads V1-V4 4, 5, 6

Critical Pitfall: ST-segment elevation can occur with massive PE causing acute right ventricular strain, particularly in anterior leads (V1-V4), and may be misdiagnosed as anteroseptal MI 4, 5, 6. Look for additional ECG findings suggesting PE: sinus tachycardia (present in 40% of PE patients), right axis deviation, new right bundle branch block, peaked P waves in lead II, or the S1Q3T3 pattern 1, 7

If Non-ST-Elevation Pattern or Equivocal ECG:

Assess for Pulmonary Embolism Risk:

• Calculate Wells score or revised Geneva score to determine pretest probability of PE 7
• Wells score components: clinical signs of DVT (3 points), PE as likely as alternative diagnosis (3 points), heart rate >100 bpm (1.5 points), immobilization/surgery within 4 weeks (1.5 points), previous PE/DVT (1.5 points), hemoptysis (1 point), malignancy (1 point) 7
• Low probability: ≤4 points (7.8% PE prevalence); High probability: >4 points (40.7% PE prevalence) 7

Apply PERC Rule for Low-Risk Patients:

• Use Pulmonary Embolism Rule-Out Criteria only if pretest probability is low (<15%) 7
• All eight PERC criteria must be met: age <50 years, pulse <100 bpm, oxygen saturation >94%, no hemoptysis, no estrogen use, no prior PE/DVT, no unilateral leg swelling, no surgery/trauma requiring hospitalization within 4 weeks 7
• If all PERC criteria met, PE is safely excluded without D-dimer or imaging 7
• Critical caveat: Do not use PERC if any criterion is violated or if pretest probability is moderate-to-high 7

D-Dimer Strategy:

• Obtain high-sensitivity D-dimer for low-to-intermediate probability patients who fail PERC criteria 7
• Use age-adjusted cutoff (age × 10 ng/mL) for patients >50 years old rather than standard 500 ng/mL threshold, which increases exclusion rate from 6.4% to 30% without additional false-negatives 7
• If D-dimer negative, PE is excluded 7
• Important limitation: D-dimer has extremely limited utility in hospitalized patients due to frequent elevation from comorbid conditions, recent surgery, infection, cancer, and inflammation—fewer than 10% of hospitalized patients will have negative D-dimer 7

Imaging Decision:

• Proceed directly to CT pulmonary angiography (CTPA) without D-dimer testing if high pretest probability (Wells score >4 points), as negative D-dimer will not obviate need for imaging 7
• Order CTPA if D-dimer is elevated in low-to-intermediate probability patients 7
• CTPA has sensitivity >95% for segmental or larger emboli and provides alternative diagnoses if PE absent (pneumonia, aortic dissection, pericardial effusion) 1, 7

Differential Diagnosis Considerations

Distinguishing MI from PE:

Features Favoring Myocardial Infarction:

• Typical anginal pain: pressure, oppression, or heaviness that is retrosternal and radiates to left arm, right arm, both arms, neck, jaw, or back 8
• Diaphoresis combined with typical pain patterns has 95% specificity and likelihood ratio of 5.18 for ACS 8
• ECG shows ST-elevation in anatomically contiguous leads corresponding to coronary artery territories 1
• Elevated troponin with rising or falling pattern (>99th percentile upper reference limit) 1

Features Favoring Pulmonary Embolism:

• Asymmetric leg swelling (present in 70% of PE patients) 7
• Pleuritic chest pain (pain worsening with deep breaths) suggesting peripheral PE with pulmonary infarction 7
• Risk factors: recent surgery/immobilization, active malignancy, previous PE/DVT, long-distance travel 7
• ECG shows sinus tachycardia (40% of PE), right axis deviation, new RBBB, peaked P waves in lead II, or S1Q3T3 pattern 1, 7
• Hypoxia with hypocapnia and respiratory alkalosis on blood gas 1

Echocardiography Role:

• Perform bedside echocardiography in hemodynamically unstable patients if CTPA not immediately available or patient too unstable for transport 1, 7
• Regional wall motion abnormalities occur within seconds of coronary occlusion but are not specific for acute MI (may represent ischemia or old infarction) 1
• Echocardiography particularly valuable for diagnosing alternative causes: acute aortic dissection, pericardial effusion, massive PE with RV dysfunction 1
• In PE, look for McConnell sign (RV mid-free wall hypokinesia with normally contracting apex), RV dilation, interventricular septal flattening, elevated RV systolic pressure 1

Management Pathways Based on Diagnosis

If STEMI Confirmed:

• Primary PCI is preferred reperfusion strategy if available within guideline-mandated timeframes 1
• Continue aspirin, initiate dual antiplatelet therapy, beta-blockers (if no contraindications), statins, and ACE inhibitors 1
• Monitor for complications: arrhythmias, heart failure, cardiogenic shock 1

If NSTEMI/Unstable Angina:

• Risk stratify using troponin levels and clinical features 1
• Initiate antiplatelet therapy (aspirin plus P2Y12 inhibitor), anticoagulation (unfractionated heparin or low-molecular-weight heparin), beta-blockers, statins 1, 3
• Early invasive strategy (angiography within 24-72 hours) for high-risk patients 1

If Pulmonary Embolism Confirmed:

• Initiate anticoagulation immediately with IV unfractionated heparin (5,000 units bolus followed by continuous infusion) or subcutaneous low-molecular-weight heparin 7, 3
• Assess hemodynamic stability: hypotension/shock indicates high-risk (massive) PE requiring consideration of thrombolysis or catheter-directed therapy 7
• For submassive PE (RV dysfunction without hypotension), close monitoring and anticoagulation alone is typically sufficient 1, 7

If Both Conditions Coexist:

• Rare but documented cases exist of simultaneous MI and PE, particularly paradoxical embolization through patent foramen ovale 1
• Treat both conditions: proceed with PCI for culprit coronary lesion while initiating anticoagulation for PE 1
• Critical warning: Heparin reduces anticoagulant effect when combined with nitroglycerin; monitor activated partial thromboplastin times closely 2

Common Pitfalls to Avoid

• Do not dismiss atypical presentations: One-third of MI patients present without chest discomfort, particularly elderly patients, women, and diabetics, who may present with isolated dyspnea, weakness, or diaphoresis 1
• Do not rely solely on troponin timing: Early troponin may be negative in acute MI; repeat measurement at 1-2 hours is essential, but do not delay reperfusion therapy waiting for results if STEMI pattern present 1
• Do not use D-dimer in high-probability patients: Proceed directly to CTPA, as negative D-dimer cannot safely exclude PE in this population 7
• Do not overlook PE mimicking STEMI: Massive PE can cause ST-elevation in anterior leads (V1-V4) and Q waves, mimicking anteroseptal MI 4, 5, 6
• Do not evaluate over telephone: Patients with chest pain and dyspnea require facility-based evaluation with ECG and biomarkers 1
• Do not delay oxygen in hypoxic patients: Administer oxygen immediately to patients with oxygen saturation <94%, breathlessness, or signs of heart failure 1