What are the differential diagnoses for a patient presenting with symptoms suggestive of a severe respiratory or cardiac condition?

Differential Diagnoses for Severe Respiratory or Cardiac Presentation

The three priority differential diagnoses that must be immediately considered are: (1) Acute Coronary Syndrome (NSTE-ACS/STEMI), (2) Pulmonary Embolism, and (3) Aortic Dissection. 1, 2

Critical Life-Threatening Diagnoses

1. Acute Coronary Syndrome (ACS)

• NSTE-ACS accounts for 15-20% of patients presenting with acute chest pain to emergency departments, with STEMI representing an additional 5-10% 1
• Typical presentation includes retrosternal chest discomfort lasting ≥10 minutes at rest or with minimal exertion, radiating to arms, neck, or jaw 1
• Atypical presentations are more common in older patients (≥75 years), women, and those with diabetes mellitus or renal insufficiency, manifesting as dyspnea, nausea, diaphoresis, or syncope without chest pain 1
• ECG must be obtained within 10 minutes of arrival to assess for ST-segment changes, with cardiac troponin drawn immediately using high-sensitivity assays 1, 2

2. Pulmonary Embolism (PE)

• PE presents with non-specific symptoms including dyspnea, chest pain, syncope, or hemoptysis, making it easily confused with ACS 1
• Approximately 25-43% of PE patients present with chest pain, and 35% have elevated troponin levels, directly mimicking acute coronary syndrome 3
• ECG changes suggestive of myocardial ischemia occur in 70% of PE patients, with ST-segment depression in V4-V6 and ST-segment elevation in V1 and aVR being particularly common in high-risk PE 3
• Central PE can cause angina-like chest pain reflecting right ventricular ischemia, requiring differentiation from ACS 1
• In hemodynamically unstable patients with suspected high-risk PE, bedside echocardiography showing RV dysfunction is sufficient to prompt immediate anticoagulation or thrombolysis 4

3. Aortic Dissection

• Aortic dissection is a life-threatening condition that must always be considered in the differential diagnosis of acute chest pain 1
• Clinical clues include back pain, unequal pulse volume between extremities, systolic blood pressure difference ≥15 mm Hg between arms, or murmur of aortic regurgitation 1
• Chest radiograph may show widened mediastinum, though CT angiography with contrast is definitive 1
• This diagnosis is critical because thrombolytic therapy or anticoagulation (appropriate for ACS or PE) would be catastrophic in aortic dissection 1

Diagnostic Approach Algorithm

Immediate Actions (Within 10 Minutes)

• Obtain 12-lead ECG immediately to evaluate for ST-segment elevation (STEMI), ST-depression/T-wave changes (NSTE-ACS), or signs of right heart strain (PE) 1, 2
• Draw high-sensitivity cardiac troponin with results available within 60 minutes 1, 2
• Assess vital signs for hypotension/shock (high-risk PE or cardiogenic shock) versus hypertension (aortic dissection) 1

Risk Stratification

• Use ESC 0h/1h algorithm for troponin with repeat sampling at 1 hour if high-sensitivity assay available, or 0h/2h algorithm as alternative 1
• Assess clinical probability of PE using Wells score or revised Geneva score if dyspnea predominates and alternative diagnosis unclear 1
• Perform bedside transthoracic echocardiography in hemodynamically unstable patients to assess RV function (PE), LV function (ACS/cardiogenic shock), and evaluate for pericardial effusion or dissection flap 2, 4

Definitive Testing

• CT pulmonary angiography (CTPA) is the definitive test for PE in hemodynamically stable patients with high clinical probability 2
• CT angiography of chest can effectively exclude pulmonary embolism, aortic dissection, and evaluate for coronary artery disease in a single study 1
• Invasive coronary angiography for NSTE-ACS based on risk stratification and troponin results 1

Critical Pitfalls to Avoid

• Never assume all symptoms are anxiety-related without thoroughly excluding organic causes, especially in elderly patients or those with cardiac risk factors 5
• PE can mimic ACS with typical anginal chest pain, elevated troponin, and ischemic ECG changes in up to one-third of cases 3, 6
• A normal ECG does not exclude ACS and occurs in 1-6% of such patients; left circumflex or right coronary occlusions can be electrically silent 1
• Do not initiate thrombolysis for suspected PE or ACS until aortic dissection is excluded, as this would be fatal 1, 4
• In suspected high-risk PE with hypotension, start heparin before diagnosis is confirmed unless contraindicated 4