What causes PR segment depression on an electrocardiogram (ECG)?

Causes of PR Segment Depression on ECG

PR segment depression on an electrocardiogram (ECG) is most commonly associated with acute pericarditis, but can also occur in other conditions including myocarditis, left circumflex artery occlusion, benign early repolarization, and takotsubo cardiomyopathy. 1, 2

Primary Causes of PR Segment Depression

1. Acute Pericarditis

• PR segment depression is present in approximately 60% of acute pericarditis cases 1
• Typically appears with these associated findings:
  • Widespread, diffuse, concave upward ST elevation
  • Reciprocal ST depression only in lead aVR
  • Four sequential stages with temporal evolution
  • No notching or slurring at terminal QRS
• Clinical context:
  • Sharp, pleuritic chest pain that improves with sitting forward
  • Possible pericardial friction rub on auscultation
  • Often preceded by respiratory illness or viral infection
  • Elevated inflammatory markers (CRP, ESR, WBC)
  • Possible pericardial effusion on echocardiography 1

2. Myocarditis/Myopericarditis

• PR depression has high sensitivity (88.2%) but moderate specificity (78.3%) for myopericarditis versus STEMI 2
• The combination of PR depressions in both precordial and limb leads has high positive predictive value (96.7%) for differentiating myopericarditis from STEMI 2
• Associated with:
  • Elevated inflammatory markers
  • Possible troponin elevation
  • Chest pain syndrome resembling acute MI with normal coronary arteries 3

3. Acute Coronary Syndromes

• Left circumflex artery occlusion can mimic the ECG pattern of pericarditis, including:
  • PR segment depression
  • Multilead ST elevation
  • ST depression in aVR 4
• Distinguishing features from pericarditis:
  • QRS widening in leads with ST elevation
  • QT interval shortening in leads with ST elevation 4

4. Benign Early Repolarization

• Can present with PR depression in inferior leads and/or PR elevation in lead aVR
• Associated findings:
  • ST elevation localized to precordial leads
  • Concave upward ST elevation
  • Characteristic notching or slurring at terminal QRS
  • Stable pattern without evolution
  • No reciprocal changes except in aVR
  • Normal inflammatory markers and cardiac biomarkers 1, 5

5. Takotsubo Cardiomyopathy

• Can show PR segment deviation patterns similar to acute pericarditis
• Characterized by:
  • PR segment elevation in aVR
  • PR segment depression in inferior leads
  • Diffuse ST segment elevations with reciprocal changes in aVR and V1 6

Diagnostic Approach to PR Segment Depression

When PR segment depression is identified on ECG, consider this algorithm:

1. Evaluate for pericarditis first:

   • Look for widespread, diffuse ST elevation with concave upward morphology
   • Check for PR depression in multiple leads (most common in lead II - 55.9%)
   • Assess for ST depression in aVR only 1, 2

2. Rule out acute coronary syndrome:

   • Look for localized ST elevation with convex morphology
   • Check for reciprocal ST depression in leads other than aVR
   • Assess for QRS widening and QT interval shortening in leads with ST elevation 4

3. Consider benign early repolarization:

   • Look for notching or slurring at terminal QRS
   • Typically localized ST elevation to precordial leads
   • Stable pattern without evolution 1, 5

4. Assess for myocarditis/myopericarditis:

   • PR depression in both precordial and limb leads
   • Elevated cardiac biomarkers
   • Possible evidence of myocardial inflammation on cardiac MRI 3, 2

5. Consider takotsubo cardiomyopathy:

   • Especially in context of recent emotional or physical stress
   • Diffuse ST elevations with reciprocal changes in aVR and V1 6

Clinical Pearls and Pitfalls

• PR segment depression is not pathognomonic for acute pericarditis alone; it can be seen in multiple conditions 5
• The most common location for PR depression in myopericarditis is lead II (55.9%), while it least commonly appears in lead aVL (2.9%) 2
• Left circumflex artery occlusion can mimic pericarditis ECG patterns, highlighting the importance of considering multiple factors in diagnosis 4
• Post-traumatic pericarditis can present with PR segment depression and normal cardiac enzymes, mimicking acute STEMI 7
• When the diagnosis is unclear, cardiac MRI can provide definitive assessment of pericardial inflammation and myocardial involvement 1

Remember that the ECG findings should always be interpreted in the clinical context, including symptoms, physical examination findings, and laboratory markers to establish the correct diagnosis.