ECG
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ECG findings in pericarditis are distinctive - classically showing diffuse saddle-shaped ST elevation across most leads with PR depression, which helps distinguish it from MI. The changes evolve through 4 stages over days to weeks.
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ECG Findings in Pericarditis
Why the ECG Changes Happen
The pericardium itself is electrically silent - ECG changes in pericarditis actually reflect subepicardial myocardial inflammation (epicarditis), which is why the term "perimyocarditis" is often more accurate. This also explains why ECG changes are seen in only ~60% of pure pericarditis cases, but in >90% when there is concomitant myocarditis. - Braunwald's Heart Disease, 10e
The 4 Stages of ECG Evolution
These changes evolve over days to weeks, though not every patient progresses through all four stages:
| Stage | PR Segment | ST Segment | T Wave |
|---|---|---|---|
| 1 (Acute) | Depressed (esp. II, aVF, V4-V6) | Diffuse elevation (I, V5, V6); ST:T ratio >0.25 | Upright |
| 2 | Isoelectric or depressed | Returns to baseline | Flattening/decreased amplitude |
| 3 | Isoelectric or depressed | Isoelectric | Diffuse T-wave inversion (I, V5, V6) |
| 4 (Resolution) | Isoelectric | Isoelectric | Normal |
- Tintinalli's Emergency Medicine
Key ECG Features - Stage 1 (What You'll See in Acute Presentation)
1. Diffuse ST Elevation
- Present in most leads: I, II, III, aVF, V2-V6
- Shape is concave upward ("saddle-shaped") - this is a key differentiator from STEMI
- Absent in aVR (which shows ST depression instead)
- Most pronounced in the lateral precordial leads (V5-V6)
2. PR Segment Depression
- Seen especially in leads II, aVF, V4-V6
- Caused by atrial injury current from epicardial inflammation spreading to the superficial atrial myocardium
- PR depression in lead aVR (PR elevation in aVR) is highly specific for pericarditis
- Can be the sole ECG manifestation in some cases
3. Reciprocal Changes - Absent
- Unlike STEMI, pericarditis does NOT produce reciprocal ST depression in other leads (except aVR/V1)
4. No Q Waves - pericarditis does not cause pathologic Q waves
5. If large effusion develops: Low QRS voltage + electrical alternans (beat-to-beat QRS axis alternation due to the heart swinging within the effusion)
ECG from Braunwald's Heart Disease - Acute Pericarditis
Note the diffuse ST-segment elevation and PR-segment depression across multiple leads.
The 4-Stage Evolution (Tintinalli's - Serial ECGs)
- A (Stage I): Diffuse ST elevation + PR depression in I, II, III, aVF
- B (Stage II): ST segments returning toward isoelectric
- C (Stage III): T-wave inversion throughout, ST now normal
How to Differentiate from STEMI and Early Repolarization
This is the most clinically important distinction.
| ECG Feature | Acute Pericarditis | Early Repolarization | STEMI |
|---|---|---|---|
| PR depression | Yes | No | No |
| ST shape | Concave (saddle) | Concave | Usually convex (tombstone) |
| ST distribution | Widespread (all leads) | Precordial + inferior | Localized (territory-specific) |
| Reciprocal ST depression | No | No | Common |
| T-wave inversion | After ST normalizes | No | Before ST normalizes |
| ST/T ratio in V6 | >0.25 | <0.25 | Variable |
| Q waves | No | No | Possible |
- Fuster and Hurst's The Heart, 15th Edition
The ST/T Ratio (Spodick's Ratio in V6)
Measure from the J point and T-wave peak in lead V6 (or lead I):
- ST amplitude ÷ T-wave amplitude > 0.25 → pericarditis likely (sensitivity >85%, specificity >80%, LR+ ~4)
- < 0.25 → early repolarization more likely (LR- ~0.2)
This is the key bedside tool when it is unclear whether you are looking at pericarditis or a normal variant.
T-Wave Inversion Timing
In pericarditis, T-wave inversion occurs after the ST segment normalizes (Stage 3). In STEMI, T-wave inversion appears before or concurrent with ST normalization. This temporal difference is diagnostically useful on serial ECGs. - Goldman-Cecil Medicine
Special Cases Where Classic ECG Changes Are Absent or Atypical
- Uremic pericarditis - typically NO ECG changes, because the epicardium is not involved in the inflammatory process
- Post-MI pericarditis (Dressler syndrome) - ECG changes may be atypical or masked by the underlying MI pattern
- Large pericardial effusion - may suppress voltages and produce electrical alternans instead of the classic ST changes
Diagnostic Criteria for Acute Pericarditis
Diagnosis requires 2 of 4 criteria:
- Typical chest pain (pleuritic, relieved by leaning forward)
- Pericardial friction rub
- Characteristic ECG changes
- Pericardial effusion on echo
ECG changes alone are not required. - Goldman-Cecil Medicine
Quick Summary Card
PERICARDITIS ECG - KEY POINTS
- Diffuse ST elevation (concave/saddle-shaped) in most leads
- PR depression (especially II, aVF, V4-V6)
- ST elevation in aVR absent (ST depression in aVR instead)
- NO reciprocal changes, NO Q waves
- 4-stage evolution over days-weeks
- ST/T ratio >0.25 in V6 = pericarditis vs early repolarization
- T inversion appears AFTER ST normalizes (not before - unlike STEMI)
- Low voltage + electrical alternans = suspect large effusion
Sources: Goldman-Cecil Medicine; Braunwald's Heart Disease; Tintinalli's Emergency Medicine; Fuster and Hurst's The Heart, 15th Ed; Rosen's Emergency Medicine
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