A systematic ECG mastery tool for medical residents & students
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Interpret
Work through 10 systematic steps to interpret any ECG — live differentials update as you go
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Reference
Criteria & Scores, Differentials, Library, Drug Effects, Electrolytes — all under the Reference menu
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Practice
Quiz, Cases, and Flashcards to reinforce your learning — under the Practice menu
Interpret ends with a final copyable report.
Complete the 10 steps, or load a sample ECG to see the full workflow.
Sample ECGs
Guidance
1
Technical Quality
Calibration & Signal Quality
1 / 10
💡 PEARL: Before interpreting any waveform, always verify machine settings. A non-standard calibration will make every measurement wrong. Standard: 10mm/mV voltage, 25mm/s paper speed.
🎓 WHY: Half-standard calibration (5mm/1mV) halves all amplitudes — you might miss LVH or significantly underestimate ST elevation.
💡 PEARL: aVL is the sentinel lead for limb lead reversal. In a normal ECG, aVR is always globally negative. If aVR positive + aVL globally negative → LA/RA reversal. Same pattern + reversed precordial R wave progression → dextrocardia. Occurs in 3–4% of all ECGs; falsely simulates MI, ectopic rhythm, and axis deviation.
🎓 WHY: Missing lead reversal means misinterpreting the entire ECG. An RA/LL reversal can fake inferior MI and trigger unnecessary cath lab activation. Three-step check before interpreting any waveform: aVR → aVL → precordial progression.
3-step diagnostic logic: aVR positive? → aVL globally negative? → Precordial progression normal or reversed? Normal progression = LA/RA reversal · Reversed progression = dextrocardia
3
Rhythm Analysis
Regularity · P Waves · AV Conduction
3 / 10
💡 PEARL: Four sub-questions. 3A: tap R-R intervals for regularity. 3B: classify P wave morphology. 3C: march P waves against QRS complexes. 3D: if more P than QRS, decide — PR lengthening (Wenckebach) or constant-then-drops (Mobitz II)?
🎓 WHY: 3A tells you if it's organized. 3B identifies the atrial focus. 3C reveals AV conduction disease. 3D distinguishes Wenckebach from Mobitz II — opposite prognoses, opposite management.
4
P-Wave & QRS Relationship
AV Conduction Mapping
4 / 10
💡 PEARL: March out P waves separately from QRS using calipers. Count each. Every P followed by QRS? Every QRS preceded by a P?
🎓 WHY: P waves marching independently of QRS = 3rd degree block. More P than QRS = 2nd degree block. Retrograde P after QRS = junctional rhythm.
5
Heart Rate
Atrial & Ventricular Rate
5 / 10
💡 PEARL: Methods: 300 ÷ (large boxes between R-R), or count QRS in 10-second strip × 6. Calculate BOTH atrial (P-P) and ventricular (R-R) rates separately.
🎓 WHY: Different atrial and ventricular rates point to AV dissociation. Narrow-complex tachycardia at exactly 150 bpm → always think atrial flutter with 2:1 block first.
💡 PEARL: Quick method — Lead I and aVF. Both positive = normal axis. Lead I pos + aVF neg = LAD. Lead I neg + aVF pos = RAD. Both negative = extreme / northwest axis.
🎓 WHY: Axis deviation narrows differentials. LAD → LAFB, inferior MI, LVH. RAD → RVH, PE, lateral MI, LPFB. Extreme → VT, hyperkalemia, or lead reversal.
7
Intervals
PR · QRS · QTc
7 / 10
💡 PEARL: PR: 120–200ms (3–5 small squares). QRS: <120ms. QTc via Bazett: QT ÷ √RR. QTc >500ms = high risk for Torsades de Pointes.
🎓 WHY: Short PR + delta wave = WPW (risk of fatal pre-excited AF). Prolonged QRS = BBB or ventricular rhythm. Always check QTc — many common drugs prolong QT.
💡 PEARL: Four sub-sections: 8A (BBB), 8B (voltage / LVH), 8C (Q waves), 8D (atrial). LVH requires voltage criteria — LAD alone is NEVER sufficient. RBBB + LAD = bifascicular block.
🎓 WHY: New LBBB + chest pain = STEMI equivalent. RBBB allows normal ST interpretation but with LAD suggests bifascicular block. Q waves indicate prior MI unless acute STE is present.
8A — QRS Morphology
Bifascicular block (RBBB + LAFB) — monitor for progression to complete heart block
LBBB present — standard ST-T interpretation unreliable. Use Sgarbossa criteria if MI suspected.
8B — Voltage Assessment (LVH / RVH)
Cornell Criteria: S in V3 + R in aVL
Cornell: ♂ ≥28mm or ♀ ≥20mm = LVH
8C — Q Waves
Select all territories with Q waves:
8D — Atrial Abnormalities
9
ST-T Analysis
Territory-by-Territory Ischaemia Screen
9 / 10
💡 PEARL: Go territory by territory: Inferior → Lateral → Anterior → aVR. Always look for reciprocal changes — they confirm ischaemia and localise the culprit vessel.
🎓 WHY: Reciprocal STD confirms ischaemia (inferior STE + lateral depression = true STEMI). aVR elevation + diffuse depression = left main or severe 3-vessel disease — emergent intervention.
Select all changes that apply — multiple selections allowed per territory.
● Inferior (II, III, aVF)
● Lateral (I, aVL, V5, V6)
● Anterior (V1–V4)
● Septal (V1–V2)
● aVR (aVR)
● Posterior (V7–V9 if obtained)
Other Findings
Global Patterns
10
Prior EKG & Clinical Context
Comparison · Symptoms · Labs · Medications
10 / 10
💡 PEARL: Compare with ANY prior EKG. Ask: is this new or old? A "new" LBBB + chest pain = cath lab. An "old" LBBB + chest pain = need Sgarbossa criteria to decide.
🎓 WHY: The single most valuable piece of information for EKG interpretation is the prior EKG — it turns a "possible abnormality" into a definite change or known baseline finding.
✓ Systematic Interpretation Complete
Now generate the final copyable interpretation report with differentials, management, and links to relevant site content.
Tip: press Enter to advance
LEAD REVERSAL DETECTED
Evolving Differential
Answer steps above to generate live differentials...
Generates structured teaching responses based on your ECG findings — not real AI inference. Uses curated guideline-based teaching points. Select a clinical question below.
⚡AI Educational AnalysisEducational purposes only
⚠️ Educational Disclaimer
AI analysis is for educational purposes only and should not replace clinical judgment. Always correlate with patient presentation, history, and physical examination.
