ECG Reference
Learn ECG interpretation
A concise reference of 48 ECG diagnoses with interpretation criteria. Each entry is what you need to recognise the pattern at a glance.
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Artifact
Channelopathies
- Wolff-Parkinson-White syndromeShort PR, delta wave, wide QRS — pre-excitation via accessory pathway.
- Long QT syndromeProlonged QTc (>460 ms men / >470 ms women), risk of torsades.
- Short QT syndromePersistently short QTc (<340 ms), tall peaked T waves; risk of VF.
- Brugada syndromeCoved ST elevation in V1-V2 (>2 mm) with negative T (type 1).
- Lown-Ganong-Levine patternShort PR (<120 ms) with normal QRS, no delta wave.
Conduction abnormalities
- 1st degree AV blockPR interval >200 ms, every P followed by QRS.
- 2nd degree AV block Mobitz I (Wenckebach)Progressive PR prolongation until a non-conducted P wave.
- 2nd degree AV block Mobitz IIConstant PR with intermittent non-conducted P waves; often wide QRS.
- Complete AV blockAtrial and ventricular activity completely dissociated.
- Right bundle branch blockQRS ≥120 ms, rsR' in V1-V2, wide S in I and V6.
- Left bundle branch blockQRS ≥120 ms, broad monophasic R in I, V5-V6, deep S in V1-V2.
- Left anterior fascicular blockLeft axis deviation (-45 to -90), qR in I and aVL, rS in II/III/aVF.
- Left posterior fascicular blockRight axis deviation, rS in I/aVL, qR in II/III/aVF (after excluding RVH and lateral MI).
Electrolyte & metabolic
Ischemia & infarction
- STEMI (anterior)ST elevation in V1-V4 with reciprocal inferior changes.
- STEMI (inferior)ST elevation in II, III, aVF with reciprocal ST depression in I/aVL.
- STEMI (lateral)ST elevation in I, aVL, V5-V6.
- Posterior STEMITall R in V1-V2 with horizontal ST depression and upright T waves.
- NSTEMI / non-ST elevation ACSST depression and/or T-wave inversion without persistent ST elevation.
- Wellens syndromeBiphasic or deeply inverted T waves in V2-V3, normal QRS, no Q waves; critical LAD stenosis.
Morphology & chamber abnormalities
- Acute pericarditisDiffuse concave ST elevation with PR depression; no reciprocal changes.
- Left ventricular hypertrophyVoltage criteria (Sokolow-Lyon ≥35 mm), often with strain pattern in lateral leads.
- Right ventricular hypertrophyRight axis deviation, dominant R in V1, deep S in V6, often RV strain.
- Pulmonary embolism (S1Q3T3 pattern)Sinus tachycardia, S in I, Q in III, inverted T in III; right heart strain.
Rhythm disorders
- Sinus rhythmNormal P before every QRS, regular rhythm, rate 60-100 bpm.
- Sinus tachycardiaSinus rhythm with rate >100 bpm.
- Sinus bradycardiaSinus rhythm with rate <60 bpm.
- Tachy-brady syndromeSick sinus syndrome with alternating tachy- and bradyarrhythmias.
- Atrial fibrillationIrregularly irregular rhythm, no discrete P waves, fibrillatory baseline.
- Atrial flutterSawtooth flutter waves, often 2:1 or 4:1 AV conduction (atrial rate ~300 bpm).
- AVNRTAV nodal reentrant tachycardia: regular narrow QRS, rate 150-220, often retrograde P buried in QRS.
- AVRT (orthodromic)Atrioventricular reentrant tachycardia using accessory pathway; narrow QRS, retrograde P after QRS.
- Premature atrial contractions (PACs)Early P wave with morphology different from sinus; non-compensatory pause.
- Premature ventricular contractions (PVCs)Wide, bizarre QRS without preceding P; full compensatory pause.
- Ventricular tachycardiaWide QRS tachycardia (>120 ms), AV dissociation, fusion/capture beats.
- Ventricular fibrillationChaotic, irregular waveforms with no identifiable QRS — cardiac arrest rhythm.
- Torsades de pointesPolymorphic VT with QRS amplitude twisting around the baseline; often QT-prolongation.
- AsystoleFlat line with no electrical activity.
- Idioventricular rhythmWide QRS escape rhythm at 20-40 bpm, no P waves preceding QRS.
- Accelerated idioventricular rhythmWide QRS rhythm at 50-110 bpm, often during reperfusion after AMI.
- Junctional rhythmNarrow QRS at 40-60 bpm, P absent or inverted in inferior leads.
- Multifocal atrial tachycardiaIrregular rhythm with ≥3 distinct P morphologies, rate >100 bpm.
- Paced rhythmPacing spikes preceding atrial and/or ventricular complexes.
- Pulseless electrical activityOrganized ECG rhythm in absence of palpable pulse — clinical, not ECG, diagnosis.