Pericarditis on the ECG

What it is

Acute pericarditis is inflammation of the pericardium, most often idiopathic or viral, and its ECG reflects inflammation of the epicardium beneath it. Because the inflammation covers the whole heart, the changes are diffuse rather than regional: concave (saddle-shaped) ST elevation in most limb and precordial leads, usually modest and rarely above 5 mm, with PR-segment depression from atrial injury. Lead aVR, which looks at the heart from the opposite side, shows the mirror image: PR elevation and ST depression, often with V1. There are no pathological Q waves, and reciprocal ST depression in other leads is absent. The changes classically evolve in four stages over days to weeks: diffuse ST elevation with PR depression; normalisation of the ST and flattening of the T waves; diffuse T-wave inversion; and a return to normal, though not every patient shows every stage. Sinus tachycardia is common. A downsloping TP segment (Spodick's sign) supports the diagnosis. A large effusion lowers the voltage of the QRS complexes, and electrical alternans, the beat-to-beat change in QRS amplitude as the heart swings in the fluid, warns of tamponade. Diagnosis needs two of four criteria: typical chest pain (sharp, pleuritic, better sitting forward), a pericardial friction rub, new widespread ST elevation or PR depression, and a new or worsening pericardial effusion; a raised CRP supports it. The ECG is normal or atypical in a good share of patients, so a normal tracing does not exclude pericarditis.

How to recognise it

• ST elevation in most leads (I, II, aVL, aVF, V2–V6), concave upwards, usually under 5 mm, not confined to one artery's territory.
• PR-segment depression in the same leads, best seen in II and the lateral precordial leads; PR elevation in aVR.
• ST depression only in aVR and often V1; no reciprocal depression elsewhere.
• No pathological Q waves and no loss of R waves.
• Sinus tachycardia is common; Spodick's sign is a downsloping TP segment.
• Large effusion: low QRS voltage (under 5 mm in all limb leads or under 10 mm in all precordial leads) and possibly electrical alternans.
• Later stages: ST returns to baseline, then T waves invert diffusely; T inversion appears after the ST has normalised, not alongside it.

Why it happens

• Inflammation of the epicardium under the pericardium causes injury currents over the whole surface of the heart, so ST elevation appears in every lead facing it.
• Atrial epicardial injury displaces the PR segment, which an infarct rarely does.
• Lead aVR faces the cavity from the right shoulder and records the opposite: PR elevation and ST depression.
• Fluid around the heart insulates it and lowers QRS voltage; a swinging heart in a large effusion gives electrical alternans.

Step by step

1. Check whether ST elevation follows one artery's territory or nearly all leads — diffuse change points to the pericardium.
2. Look for PR depression in II and V5–V6 and PR elevation in aVR — atrial injury is specific to pericarditis.
3. Search for reciprocal ST depression outside aVR and V1 — if present, think infarction first.
4. Check for Q waves and T inversion — they argue for infarction or myocardial involvement.
5. Assess QRS voltage and beat-to-beat alternans — a large effusion or tamponade changes the urgency.
6. Compare with earlier tracings and repeat in a few hours — STEMI evolves fast; pericarditis changes over days.

Differential and pitfalls

• STEMI: regional ST elevation, often convex, with reciprocal depression, Q waves, and ST and T changes evolving within hours.
• Benign early repolarisation: J-point notching, no PR depression, stable over time; ST/T ratio in V6 above 0.25 favours pericarditis.
• Myopericarditis: pericarditis with a raised troponin; it changes the work-up and the advice on exercise.
• Pitfall: atypical or normal ECG in many patients; the diagnosis rests on the 2-of-4 criteria, not on the tracing alone.
• Pitfall: T inversion during the ST-elevation stage suggests myocardial involvement or infarction, not simple pericarditis.
• Constrictive pericarditis and chronic effusions give low voltage and non-specific T changes, not the acute pattern.

Next step

• Request troponin, CRP, a chest X-ray and an echocardiogram in every suspected case.
• Any doubt between pericarditis and STEMI: call cardiology at once; do not give fibrinolysis for a pericarditis tracing.
• Low voltage, alternans, hypotension or raised JVP: urgent echo and senior review for tamponade.
• Admit high-risk features: fever, subacute onset, large effusion or tamponade, raised troponin, immunosuppression, trauma, anticoagulation, no response to NSAIDs.
• Low-risk cases: NSAID or aspirin plus colchicine as the protocol sets, exercise restriction and review within 1 to 2 weeks.

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Elsewhere in DurgiPedia

• The ECG in ischemia and infarction
• ECG basics: waves, intervals and leads
• Chest pain: ischemic, pericardial, pleural and other patterns
• Pericardial disease

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Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: Pericarditis (StatPearls (NCBI Bookshelf), 2026).

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