What is the most likely diagnosis for a patient with sharp epigastric pain that worsens with inspiration and on lying flat, recent chest infection, diffuse inspiratory crepitations, normal oxygen saturation, and ECG showing widespread saddle-shaped ST elevation?

Acute Pericarditis

The most likely diagnosis is acute pericarditis (Option A), based on the classic triad of sharp chest pain that worsens with inspiration and lying flat, recent viral illness (chest infection), and the pathognomonic ECG finding of widespread saddle-shaped ST elevation.

Key Diagnostic Features Present

The patient demonstrates the hallmark clinical presentation of acute pericarditis:

• Sharp, pleuritic chest pain that increases with inspiration and lying supine is characteristic of pericarditis and makes ischemic heart disease unlikely 1
• Widespread saddle-shaped ST elevation on ECG is the electrocardiographic hallmark of pericarditis, typically accompanied by PR segment depression 1
• Recent chest infection provides the viral prodrome commonly seen before acute pericarditis 1
• Normal oxygen saturation (98%) argues against significant pulmonary pathology like pulmonary embolism 2

Why Other Diagnoses Are Excluded

Myocardial infarction (Option C) and angina (Option B) are effectively ruled out because:

• Sharp chest pain that increases with inspiration and lying supine is unlikely related to ischemic heart disease 1
• Anginal symptoms are typically described as retrosternal pressure, heaviness, or tightness—not sharp pain 1
• Positional chest pain is usually nonischemic 1
• Widespread ST elevation in pericarditis differs from the regional ST elevation seen in STEMI 1

Pleurisy (Option D) is less likely because:

• While pleuritic pain is present, the widespread ECG changes point to pericardial rather than purely pleural pathology 1
• The ECG findings of widespread saddle-shaped ST elevation are diagnostic for pericarditis, not pleurisy 1

Pulmonary embolism (Option E) is excluded by:

• Normal oxygen saturation makes significant PE unlikely 2
• PE typically presents with tachycardia and dyspnea in >90% of patients 1
• The widespread ST elevation pattern is not consistent with PE 2

Clinical Reasoning Algorithm

When evaluating chest pain with pleuritic features:

1. Obtain ECG immediately (within 10 minutes) to identify life-threatening causes 1, 2
2. Assess pain characteristics: Sharp pain worse with inspiration and position changes suggests pericarditis rather than ACS 1
3. Evaluate ECG pattern: Widespread saddle-shaped ST elevation with PR depression is pathognomonic for pericarditis 1
4. Consider recent viral illness: A preceding respiratory infection supports pericarditis diagnosis 1
5. Check vital signs and oxygen saturation: Normal values help exclude PE and pneumothorax 2

Important Clinical Pitfalls

• Do not assume sharp, pleuritic pain excludes cardiac pathology—while it makes ischemia less likely, pericarditis is still a cardiac diagnosis requiring specific management 1, 2
• Pericardial friction rub is only audible in one-third of patients, so its absence does not exclude pericarditis 1
• Small pericardial effusion is present in only 60% of acute pericarditis cases, so normal echocardiography does not rule out the diagnosis 1
• Elevated troponin may occur in up to 50% of pericarditis cases (termed perimyocarditis), reflecting myocardial involvement in the inflammatory process 1