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📖 ECG from Basics to Expertise — A Complete Resident's Guide

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PART 1: WHY THE ECG LOOKS THE WAY IT DOES

The Conduction System (Start Here)

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PART 2: THE ECG PAPER & RECORDING BASICS

• Paper speed: 25 mm/s
• 1 small square = 1 mm = 0.04 s
• 1 large square = 5 mm = 0.20 s
• Amplitude standard: 10 mm = 1 mV

The 12 Leads

• Bipolar: I (RA→LA), II (RA→LL), III (LA→LL)
• Augmented unipolar: aVR (right arm), aVL (left arm), aVF (left foot)

• V1: Right sternal border, 4th ICS
• V2: Left sternal border, 4th ICS
• V3: Between V2 and V4
• V4: Left midclavicular line, 5th ICS
• V5: Left anterior axillary line
• V6: Left midaxillary line

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PART 3: THE WAVES, INTERVALS & SEGMENTS

Normal Values (Adults)

QTc (Corrected QT)

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PART 4: A SYSTEMATIC 8-STEP APPROACH (Never Skip)

Step 1: Rate

• 1 box = 300 bpm | 2 = 150 | 3 = 100 | 4 = 75 | 5 = 60 | 6 = 50

Step 2: Rhythm

1. Is there a P wave before every QRS?
2. Is the P wave upright in leads I and aVF? (= sinus origin)
3. Is the RR interval regular?

Step 3: Axis

Step 4: P Wave

• Broad, notched P in lead II (P mitrale, > 0.12 s) → Left atrial enlargement
• Tall, peaked P in lead II (P pulmonale, > 2.5 mm) → Right atrial enlargement
• No visible P waves → Atrial fibrillation/flutter/junctional rhythm

Step 5: PR Interval

Step 6: QRS Complex

• Width > 0.12 s = bundle branch block or ventricular rhythm
• RBBB pattern (RSR' in V1, slurred S in I and V6): RV depolarizes last via slow muscle spread
• LBBB pattern (broad notched R in I, V5, V6; QS in V1): LV depolarizes last — invalidates ischemia interpretation
• Q waves: Pathologic if > 0.04 s wide OR > 25% of R wave height in the same lead → old MI
• R wave progression: R should grow from V1→V5. Poor R wave progression → anterior MI

Step 7: ST Segment & T Wave

Step 8: QT Interval & Other Findings

• Prolonged QT: Risk of torsades de pointes. Causes: drugs (antipsychotics, antiarrhythmics, antibiotics), hypokalemia, hypomagnesemia, hypocalcemia, congenital LQTS
• Short QT: Hypercalcemia, digoxin, short QT syndrome
• Delta wave (slurred QRS upstroke): Wolff-Parkinson-White syndrome

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PART 5: COMMON ECG PATTERNS YOU MUST MASTER

Atrial Fibrillation

• Irregularly irregular RR intervals
• No distinct P waves — chaotic baseline
• Narrow QRS (unless aberrant conduction or pre-existing BBB)

Atrial Flutter

• Sawtooth flutter waves at ~300 bpm, typically 2:1 or 4:1 conduction
• Ventricular rate 150 bpm (2:1) or 75 bpm (4:1)
• Best seen in II, III, aVF

SVT (Narrow Complex Tachycardia)

• Rate 150–250 bpm, regular
• P waves often buried in QRS or retrograde
• Responds to adenosine (also diagnostic)

Ventricular Tachycardia (VT)

• Wide QRS (> 0.12 s), rate > 100 bpm
• AV dissociation = diagnostic
• Fusion beats and capture beats = pathognomonic
• Brugada criteria / Vereckei algorithm: helps distinguish VT from SVT with aberrancy

Hyperkalemia — Progressive Changes

1. Peaked T waves (K > 5.5)
2. Widened QRS (K > 6.5)
3. Flattened/absent P waves (K > 7)
4. Sine wave pattern → VF

Pulmonary Embolism — S1Q3T3

• S wave in lead I
• Q wave in lead III
• T wave inversion in lead III
• Sinus tachycardia (most common finding)
• Rightward axis, RBBB, T inversion V1–V4 (right heart strain)

Pericarditis

• Diffuse concave ("saddle-shaped") ST elevation in almost all leads
• PR depression (especially lead II) — very specific sign
• No reciprocal changes (unlike MI)

Left Ventricular Hypertrophy (Sokolow-Lyon criteria)

• S in V1 + R in V5 or V6 > 35 mm
• R in aVL > 11 mm
• Associated with ST depression and T wave inversion ("strain pattern") in lateral leads

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PART 6: KEY DIAGNOSES FROM BRAUNWALD'S — CLINICAL ECG UTILITY

• QT prolongation → Long-QT syndrome
• Short PR + delta wave → Wolff-Parkinson-White syndrome
• RBBB + ST elevation in V1–V2 → Brugada syndrome
• T wave inversion in right precordial leads → Arrhythmogenic RV dysplasia (ARVC)
• High-grade AV block → Stokes-Adams attacks

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PART 7: HOW TO BECOME AN EXPERT — ROADMAP

Phase 1 — Build the Foundation (Months 1–2)

1. Memorize the 8-step systematic approach — apply it to every ECG you touch, even if it looks "obviously normal"
2. Read: ECG Made Easy by Akhtar & Hampton — short, practical primer
3. Ganong's physiology chapter on cardiac electrophysiology — understand WHY waveforms form
4. Practice 5–10 ECGs daily on ECGWaves.com or Life in the Fast Lane ECG Library

Phase 2 — Pattern Recognition (Months 3–4)

1. Master the STEMI mimics: early repolarization, LVH, LBBB, pericarditis, hyperkalemia, Brugada
2. Learn Sgarbossa criteria for STEMI in LBBB/paced rhythms (modified: concordant STE ≥ 1 mm, or discordant STE ≥ 25% of S-wave depth)
3. Use Dr. Smith's ECG Blog (https://hqmeded-ecg.blogspot.com) — expert commentary on real, difficult cases daily

Phase 3 — Advanced Interpretation (Months 5–8)

1. Study Wellens' syndrome (biphasic/deep T inversion in V2–V3 = proximal LAD critical stenosis — do NOT stress test)
2. Learn de Winter T waves (upsloping ST depression + tall T in precordial leads = LAD occlusion with no STE)
3. Master AV block grades, fascicular blocks, and bifascicular/trifascicular block
4. Attend a dedicated advanced ECG workshop (EP fellows often run these)

Phase 4 — Expert (Month 9+)

1. Correlate every ECG with clinical outcome — build mental case libraries
2. Read Marriott's Practical Electrocardiography or Chou's Electrocardiography in Clinical Practice
3. Present ECGs at cardiology conferences / morbidity & mortality rounds
4. Learn to interpret electrophysiology tracings in the cath lab context

Daily Habits of Expert ECG Readers

• Always read the ECG before looking at the computer interpretation (machines are wrong ~30% of the time)
• Commit to a written systematic interpretation — don't just glance
• Compare with prior ECGs — dynamic change is often more important than any single finding
• When in doubt: call cardiology; ECG misinterpretation in AMI is a major medicolegal issue

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PART 8: QUICK REFERENCE CARD

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• Ganong's Review of Medical Physiology, 26th ed. — Chapters 29 (cardiac electrophysiology, ECG basics)
• Braunwald's Heart Disease, 2-Volume Set — Chapter 71 (syncope workup and ECG role)
• Tintinalli's Emergency Medicine — Chapters 49, 51 (ACS, chest pain ECG interpretation)
• Harriet Lane Handbook, 23rd ed. — Chapter 7 (systematic ECG approach, normal parameters table)