What are the diagnostic criteria and steps for diagnosing acute pericarditis?

Diagnosis of Acute Pericarditis

The diagnosis of acute pericarditis requires at least 2 of the following 4 clinical criteria: pericarditic chest pain, pericardial friction rub, new widespread ST-elevation or PR depression on ECG, or new/worsening pericardial effusion. 1

Diagnostic Criteria (≥2 Required)

1. Pericarditic Chest Pain (~90% of cases)

• Sharp, pleuritic, retrosternal pain that worsens with inspiration and when lying supine 2
• Improves with sitting up and leaning forward 3
• May radiate to the neck, back, or left shoulder (trapezius ridge is characteristic) 1, 3

2. Pericardial Friction Rub (<30-33% of cases)

• Highly specific but transient finding representing friction between inflamed pericardial layers 1, 2
• Best heard at the left lower sternal border with the patient sitting upright, leaning forward, and briefly holding their breath 3
• Can be mono-, bi-, or triphasic (triphasic is most characteristic) 3
• May disappear and reappear during the illness, requiring repeated auscultatory examinations 3
• Absence does not exclude pericarditis 3

3. ECG Changes (25-60% of cases)

• New widespread ST-segment elevation (concave upward) without reciprocal changes 1, 4
• PR-segment depression in multiple leads 1, 4
• T-wave inversions may develop later 4
• ECG changes imply epicardial inflammation, as the parietal pericardium is electrically inert 1
• Major differential diagnosis is acute coronary syndrome with ST-elevation (which shows localized convex ST elevation) 1, 3

4. Pericardial Effusion (~60% of cases)

• New or worsening fluid collection detected by imaging 1, 2
• Most often small in acute pericarditis 2

Essential Diagnostic Workup

Immediate Testing

• Electrocardiogram (within 10 minutes of presentation) 3
• Transthoracic echocardiography in all patients with suspected pericarditis to detect effusion, assess for tamponade, and evaluate ventricular function 1, 5, 4
• Chest X-ray (often normal unless effusion exceeds 300 mL) 1, 3

Laboratory Studies (Supporting Findings)

• Inflammatory markers: C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and white blood cell count 1, 6
  • Elevated in most cases and useful for monitoring disease activity and treatment response 1
  • Normal inflammatory markers do not exclude pericarditis, especially if already on anti-inflammatory treatment 5, 6
• Cardiac biomarkers (troponin, creatine kinase) 1, 6
  • Elevated in up to 50% of cases, indicating concomitant myocarditis (myopericarditis) 3, 2
  • Elevation indicates myocardial involvement rather than primary pericardial disease 5

Advanced Imaging (When Indicated)

• Cardiac MRI is the preferred advanced imaging modality when echocardiography is nondiagnostic or there is diagnostic uncertainty 5
  • 94-100% sensitivity for detecting pericardial inflammation 5
  • Can distinguish myopericarditis from other cardiomyopathies 5
• Cardiac CT with IV contrast (not CT angiography) may be used when MRI is contraindicated or to evaluate for pericardial calcification/thickening 5

Diagnostic Algorithm

1. Assess for ≥2 of the 4 diagnostic criteria (chest pain, friction rub, ECG changes, effusion) 1
2. Perform transthoracic echocardiography in all suspected cases 1, 5
3. Obtain inflammatory markers and cardiac biomarkers 1, 6
4. If diagnosis remains uncertain, proceed to cardiac MRI 5
5. Rule out acute coronary syndrome when ST-elevation is present (localized convex ST-elevation, reciprocal changes, and troponin elevation favor MI) 1, 3

Common Pitfalls and Caveats

• ECG changes may be absent in up to 40% of cases 5
• Pericardial friction rub is only audible in approximately one-third of patients and can be intermittent 3, 2
• Normal echocardiogram does not exclude pericarditis (effusion present in only ~60% of cases) 3, 2
• Troponin elevation indicates myopericarditis, not exclusion of the diagnosis 5, 3
• Do not use nitroglycerin response as a diagnostic criterion (relief does not confirm or exclude pericarditis) 3
• Uremic pericarditis may be asymptomatic and lack typical ECG changes 3
• CT angiography is not appropriate for pericarditis evaluation; use cardiac CT with IV contrast if CT is needed 5