EKG Changes in Acute Pericarditis
The characteristic EKG finding in acute pericarditis is widespread ST-segment elevation (concave upward) with PR-segment depression, though these classic changes appear in only 25-60% of cases. 1, 2
Primary Diagnostic EKG Criteria
According to the 2015 ESC Guidelines, new widespread ST-elevation or PR depression on ECG is one of the four diagnostic criteria for acute pericarditis (at least 2 of 4 criteria needed for diagnosis) 1. However, it's critical to understand that:
- Only 25-50% of patients show the classic widespread ST-elevation and PR depression pattern 2
- Up to 60% of cases demonstrate typical ECG changes overall 1
- The ECG may be completely normal at initial presentation or for days after symptom onset 3
Key EKG Features to Identify:
ST-Segment Changes:
- Widespread, concave-upward ST-segment elevation (diffuse across multiple leads) 4, 5
- Distinguishes from acute MI where ST-elevation is typically convex and localized to a vascular territory
PR-Segment Changes:
Critical Discriminating Feature: ST/T Ratio
An ST/T ratio ≥0.25 in lead V6 has 100% positive and negative predictive value for distinguishing acute pericarditis from normal variant ST changes 6. This is the single most reliable quantitative criterion:
- If V6 unavailable, use ST/T ratio ≥0.24 in leads V5, V4, or I (PPV 0.80-0.87, NPV 0.81-1.0) 6
- T-wave amplitude ≤0.3 mV in V6 also suggests pericarditis (PPV and NPV both 0.85) 6
Temporal Evolution and Pitfalls
Common Pitfall: ECG changes are temporally dynamic and evolve rapidly during disease course 3. Serial ECGs are essential because:
- Initial ECG may be normal
- Changes are influenced by disease severity, timing of presentation, degree of myocardial involvement, and treatment initiated 3
- New ST-elevation patterns may appear during recurrent chest pain episodes 3
Differential Diagnosis on EKG
Must distinguish from:
- Acute MI: ST-elevation is convex (not concave), localized to coronary territory, often with reciprocal depression, and associated with Q-waves
- Early repolarization: Lower ST/T ratios (<0.25), typically in young healthy individuals 6, 4
Clinical Context
Remember that ECG changes reflect epicardial inflammation, not pericardial inflammation (the parietal pericardium is electrically inert) 1. This explains why:
- Patients with isolated pericardial inflammation may have normal ECGs
- Concomitant myocarditis increases likelihood of ECG changes
- The presence of myocardial involvement may elevate troponin levels 1
Recommendation: Always obtain an ECG in all patients with suspected acute pericarditis (Class I, Level C recommendation) 1, but recognize its limitations. When ECG is normal or equivocal, rely on other diagnostic criteria (chest pain characteristics, pericardial rub, effusion on echo, elevated inflammatory markers) and consider serial ECGs to capture evolving changes 3.