• Cardiology - heart failure, arrhythmias, ACS, valvular disease
• Respiratory - COPD, asthma, pneumonia, TB, lung cancer
• Nephrology - AKI, CKD, glomerulonephritis, electrolyte disorders
• Gastroenterology - liver disease, IBD, GI bleeding, pancreatitis
• Endocrinology - diabetes, thyroid, adrenal, pituitary disorders
• Neurology - stroke, epilepsy, meningitis, movement disorders
• Infectious Disease - antibiotics, tropical medicine, sepsis
• Hematology/Oncology - anemias, leukemias, coagulation disorders
• Rheumatology - SLE, RA, vasculitis, crystal arthropathies
• Pharmacology - drug mechanisms, side effects, interactions

• Explain concepts and pathophysiology clearly
• High-yield MCQ-style questions with explanations
• Mnemonics and memory aids
• Differentials and clinical reasoning
• Quick revision summaries
• Recent evidence and guidelines

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ECG Mastery: Basics to Advanced

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MODULE 1 - Why ECG? The Big Picture

• Rhythm and rate
• Conduction system integrity
• Chamber size (hypertrophy)
• Ischemia and infarction (location, age, extent)
• Metabolic/electrolyte status
• Drug effects
• Pericardial disease

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MODULE 2 - The Cardiac Conduction System

SA Node (right atrium)
    ↓  (atrial depolarization = P wave)
AV Node (PR delay = AV node slowing)
    ↓
Bundle of His
    ↓
Right Bundle Branch  +  Left Bundle Branch
                            ↙         ↘
                    Left Anterior   Left Posterior
                      Fascicle        Fascicle
    ↓
Purkinje Fibers → Ventricular myocardium (= QRS)

• SA node fires at 60-100/min (dominant pacemaker)
• AV node fires at 40-60/min if SA fails (junctional escape)
• Purkinje / ventricle fires at 20-40/min (ventricular escape)
• Ventricular repolarization = ST segment + T wave

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MODULE 3 - ECG Paper and Calibration

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MODULE 4 - ECG Waveforms and Intervals

The Waves

The Intervals

• Regular rhythm: HR = 300 ÷ (number of large squares between R-R)
• Or: HR = 1500 ÷ (number of small squares between R-R)
• Irregular: count QRS complexes in 10-second strip × 6

1 large square = 300 bpm | 2 = 150 | 3 = 100 | 4 = 75 | 5 = 60 | 6 = 50

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MODULE 5 - The 12 Leads (Understanding the "Camera Angles")

Limb Leads (Frontal Plane)

Precordial Leads (Horizontal Plane)

Grouping Leads by Territory

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MODULE 6 - The Normal ECG (What to Expect)

Normal Sinus Rhythm Checklist

• Rate: 60-100 bpm
• P wave before every QRS; QRS after every P
• PR interval: 120-200 ms
• P wave: upright in I, II; inverted in aVR
• QRS: <110 ms, normal axis (-30° to +90°)
• R-wave progression in V1-V6 (R grows from V1 to V5)

P Wave Morphology

• Right atrial enlargement (P pulmonale): P wave >2.5 mm tall in II (peaked)
• Left atrial enlargement (P mitrale): P wave >120 ms wide, notched in II; terminal negative deflection in V1 >1 mm² (>1 small square wide AND deep)

QRS Axis

• Both upright → Normal
• I up, aVF down → Left axis
• I down, aVF up → Right axis
• Both down → Extreme axis

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MODULE 7 - Chamber Enlargement / Hypertrophy

Left Ventricular Hypertrophy (LVH)

• S in V1 + R in V5 or V6 ≥ 35 mm
• R in aVL ≥ 11 mm (Cornell criteria)
• Associated with: LV strain pattern (ST depression + T wave inversion in lateral leads I, aVL, V5, V6)

Right Ventricular Hypertrophy (RVH)

• R ≥ S in V1 (dominant R in V1)
• RAD (axis >+90°)
• rSR' in V1 is NOT RVH - that is RBBB
• ST depression + T wave inversion in V1-V3 (RV strain)

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MODULE 8 - Bundle Branch Blocks

Right Bundle Branch Block (RBBB)

• QRS ≥ 120 ms
• RSR' ("M-shaped" or "rabbit ears") in V1
• Wide, slurred S wave in I, V5, V6
• T wave inverted in V1 (secondary change - normal with RBBB)

RBBB = bunny ears in V1 (rSR' = ears of a rabbit)

Left Bundle Branch Block (LBBB)

• QRS ≥ 120 ms
• Broad, notched R (no Q, no S) in I, aVL, V5, V6
• rS or QS (deep S) in V1, V2
• T wave opposite to main QRS deflection (secondary change)

• LBBB: W in V1, M in V6
• RBBB: M in V1, W in V6

Fascicular Blocks (Hemiblocks)

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MODULE 9 - AV Blocks

First Degree AV Block

• PR interval > 200 ms (>1 large square)
• Every P conducts to QRS (just slowly)
• Usually benign; can be normal in athletes

Second Degree AV Block

• Progressive PR lengthening until a P wave is blocked (QRS dropped)
• "Longer, longer, longer, DROP - then you have a Wenckebach"
• PR after the dropped beat is shortest
• Usually at AV node level; generally benign
• Can be normal in athletes (vagal tone)

• Fixed PR interval; sudden non-conducted P wave (QRS drops without warning)
• Below AV node (His-Purkinje level) - more serious
• Often associated with wide QRS
• High risk of progressing to complete heart block → needs pacemaker

Third Degree (Complete) AV Block

• Complete dissociation: P waves and QRS complexes march independently
• P rate > QRS rate
• QRS escape rhythm: narrow (junctional, 40-60/min) or wide (ventricular, 20-40/min)
• Wide-complex escape = more severe (infranodal block)
• Emergency: Atropine (for narrow-complex), transcutaneous pacing, then permanent pacemaker

Wenckebach = Increasing PR before drop (I = Increasing) Mobitz II = Suddenly drops (II = abrupt, Sudden)

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MODULE 10 - Ischemia and Infarction

Spectrum of Ischemic ECG Changes

• Tall, broad, peaked T waves over ischemic zone
• First sign of complete coronary occlusion

• ST elevation in ≥2 contiguous leads
• Threshold: ≥1 mm (most leads), ≥2 mm (V1-V3 men), ≥1.5 mm (V1-V3 women)
• Represents full-thickness (transmural) injury
• Mechanism: epicardial injury current shifts ST vector outward

• Horizontal or downsloping ST depression ≥0.5-1 mm
• Mechanism: ischemia confined to subendocardium; ST vector shifts inward

• Symmetric, deep T wave inversions
• Wellens' syndrome: deep T inversions in V2-V3 = critical proximal LAD stenosis (do NOT stress test - risk of VF)

• Width ≥ 40 ms (1 small square)
• Depth ≥ 25% of R wave height in same lead
• Represent electrically dead (necrotic) myocardium
• Q waves in II, III, aVF = inferior MI; V1-V4 = anterior MI; I, aVL = lateral MI

Localization of STEMI

Evolution of STEMI Over Time

Minutes:    Hyperacute T waves (peaked, tall)
Hours:      ST elevation (convex/"tombstone" shape)
6-24h:      ST elevation + Q waves appear + T inversion begins
Days:       ST returns to baseline + T waves inverted + Q waves persist
Weeks-mos:  ST and T normalize; Q waves often persist permanently

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MODULE 11 - Arrhythmias

Approach to Any Arrhythmia (systematic)

1. Rate: Fast / slow / normal?
2. Regular or irregular?
3. QRS wide or narrow?
4. P waves present? What is the relationship to QRS?

Narrow Complex Tachycardias (QRS < 120 ms)

Wide Complex Tachycardias (QRS ≥ 120 ms) - THE HIGH-STAKES AREA

1. VT (ventricular tachycardia) - most dangerous, assume this first
2. SVT with aberrant conduction (LBBB/RBBB)
3. SVT with pre-excitation (WPW with AF = most dangerous SVT)
4. Pacemaker-mediated tachycardia

If in doubt, treat wide complex tachycardia as VT until proven otherwise Never give adenosine or verapamil to pre-excited AF (WPW+AF) - can precipitate VF

• AV dissociation (P waves marching independently) = definitive VT
• Capture beats (narrow QRS among wide) = definitive VT
• Fusion beats = definitive VT
• QRS duration > 160 ms
• Concordance (all precordial leads all-positive or all-negative)
• NW (extreme) axis deviation

Bradyarrhythmias

Ventricular Arrhythmias

• Wide (>120 ms), bizarre QRS
• No preceding P wave
• Compensatory pause
• Bigeminy (every other beat), trigeminy (every third)

• ≥3 consecutive wide QRS complexes at ≥100 bpm
• Sustained (>30 s) vs non-sustained (<30 s)
• Monomorphic (uniform QRS) vs polymorphic (varying QRS)

• Polymorphic VT with twisting QRS axis around baseline
• Occurs with long QT (congenital or acquired)
• Triggers: hypokalemia, hypomagnesemia, drugs (class IA/III antiarrhythmics, antipsychotics, antibiotics like azithromycin)
• Treatment: IV magnesium sulfate; correct electrolytes; stop offending drug

• Chaotic, irregular deflections, no organized QRS
• No cardiac output = cardiac arrest
• Immediate defibrillation + CPR

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MODULE 12 - Pre-excitation (WPW Syndrome)

• Short PR interval (<120 ms) - bypass of AV node
• Delta wave - slurred upstroke of QRS
• Wide QRS (>110 ms) - fusion of normal and accessory pathway conduction
• ST-T changes secondary to abnormal depolarization

• Positive delta in V1-V3, negative in aVL = left-sided pathway (most common)
• Negative delta in II, III, aVF = posterior/inferior pathway

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MODULE 13 - Metabolic and Drug Effects

Hyperkalemia (sequential changes as K+ rises)

Hypokalemia

• Flattened T waves
• Prominent U waves (U > T wave height = significant)
• Apparent QT prolongation (actually QU prolongation)
• Risk of Torsades

Hypercalcemia

• Shortened QT interval
• Short ST segment or absent ST

Hypocalcemia

• Prolonged QT (prolonged ST segment)
• T wave remains normal

Digoxin

• "Reverse tick" or "Salvador Dali mustache" ST depression (scooping)
• Shortened QT
• T wave flattening or inversion
• Digoxin toxicity: PAT with block, ventricular bigeminy, PVCs, AV blocks

Hypothermia

• Bradycardia
• Osborn (J) wave: positive deflection at J point (most visible in V5, V6)
• Prolonged PR, QRS, QT
• Shivering artifact

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MODULE 14 - Pericarditis vs. STEMI

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MODULE 15 - Pulmonary Embolism ECG

• Deep S wave in Lead I
• Q wave in Lead III
• T wave inversion in Lead III

• Sinus tachycardia (most common sign)
• New RBBB (acute right heart strain)
• RAD
• T wave inversions V1-V4 (RV strain pattern)
• Atrial arrhythmias (AF, flutter)
• P pulmonale

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MODULE 16 - The Brugada Pattern

• Coved (convex) ST elevation ≥2 mm in V1-V2
• Down-sloping ST segment followed by T wave inversion
• Spontaneous or drug-induced

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MODULE 17 - The 14-Step Systematic ECG Approach (Exam and Clinical)

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MODULE 18 - High-Yield Exam Mnemonics

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MODULE 19 - Quick Clinical Decision Rules

• ST elevation ≥1 mm in ≥2 contiguous leads → Activate cath lab (STEMI protocol) - door to balloon <90 min
• New LBBB + chest pain → Same as STEMI (Sgarbossa criteria)
• ST depression V1-V4 + inferior STEMI → Posterior MI; do V7-V9
• Inferior STEMI + hypotension + clear lungs → Rule out RV MI with V4R

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Suggested Study Order for Exams

1. Paper calibration + waveform basics (Module 3, 4)
2. Leads and normal ECG (Module 5, 6)
3. Ischemia/STEMI localization (Module 10) - highest exam yield
4. Bundle branch blocks (Module 8)
5. AV blocks (Module 9)
6. Arrhythmias systematic approach (Module 11)
7. Metabolic effects (Module 13)
8. Practice 14-step approach on real ECGs (Module 17)

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ECG Visual Atlas: Stepwise Learning with Real ECGs

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LEVEL 1 - The Foundation

ECG 1: Normal Sinus Rhythm - Your Baseline

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ECG 2: Ventricular Depolarization - How the QRS is Born

• Phase 1 (septum): Depolarizes left → right. V1 sees it coming → small upward r wave. V6 sees it going away → small downward q wave.
• Phase 2 (ventricles): LV dominates, vector swings left → right. V1 sees it going away → deep S wave. V6 sees it coming → tall R wave.

• V1 = rS (small r, big S)
• V6 = qR (tiny q, big R)
• V1 → V5 = R wave progressively gets bigger (R-wave progression)

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LEVEL 2 - Atrial and Ventricular Enlargement

ECG 3: P Wave Morphology - Atrial Abnormalities

• RAE (P pulmonale): COPD, pulmonary hypertension, tricuspid stenosis, PE
• LAE (P mitrale): Mitral stenosis, mitral regurgitation, LVH, dilated cardiomyopathy

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ECG 4: LVH and RVH Patterns

• S in V1 + R in V5 or V6 ≥ 35 mm
• R in aVL ≥ 11 mm (women); ≥ 28 mm (men) - Cornell criteria
• LV strain pattern: ST depression + asymmetric T inversion in I, aVL, V5, V6

• Dominant R wave in V1 (R ≥ S in V1)
• Right axis deviation (axis > +90°)
• RV strain pattern: T inversion in V1-V3

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LEVEL 3 - Ischemia and Infarction (Highest Exam Yield)

ECG 5: The Mechanism of ST Deviation

• Panel A (Subendocardial ischemia): Injury current vector points inward → leads overlying the LV see ST depression. This is NSTEMI/unstable angina territory.
• Panel B (Transmural/epicardial ischemia): Injury current vector points outward → leads overlying the zone see ST elevation. This is STEMI territory.

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ECG 6: Anterior STEMI (LAD occlusion)

• ST elevation in V1-V4 (anteroseptal leads) - convex/oblique ST morphology
• Note the tall R waves progressing V1-V4, then cut short by the ST change
• This patient had a 90% LAD stenosis - went to cath lab immediately

1. Rate: ~70 bpm, sinus
2. ST elevation: V1, V2, V3, V4 - ≥2 mm in V1-V3 = diagnostic STEMI
3. Reciprocal changes: Look for ST depression in II, III, aVF (inferior leads)
4. Q waves: May be developing - marker of established necrosis
5. ACTION: Activate cath lab. Door-to-balloon time target: <90 min

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ECG 7: Anterolateral STEMI (LAD + circumflex territory)

• ST elevation spreading across V2-V6, I, and aVL = extensive anterolateral territory
• This is a large territory MI - "widowmaker" territory (proximal LAD)
• Patient had in-stent thrombosis of previous LAD stent

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ECG 8: Wellens Syndrome (Critical LAD Stenosis Warning)

• Deep, symmetric T-wave inversions in V2-V4 (precordial leads)
• Note: no current ST elevation, R waves preserved (no Q waves yet)
• Patient had chest pain that may have resolved

⚠️ DO NOT do a stress test on this patient - can precipitate VF and death. Refer urgently for coronary angiography.

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ECG 9: Left Main / Proximal LAD Occlusion - aVR Elevation

• ST elevation in aVR > 1 mV (the lead pointing at the right shoulder / LV cavity)
• Widespread ST depression in most other leads (I, II, aVL, V4-V6 at minimum)
• This pattern = diffuse subendocardial ischemia from left main occlusion

ST elevation in aVR + widespread ST depression elsewhere = Left main stenosis (78% sensitive, 83% specific) or severe proximal LAD disease

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LEVEL 4 - Bundle Branch Blocks

ECG 10: RBBB vs LBBB - The WiLLiaM MaRRow Rule

• WiLLiam = LBBB has W in V1, M in V6
• MaRRow = RBBB has M in V1, W in V6

• QRS ≥ 120 ms
• rSR' ("rabbit ears") in V1
• Wide slurred S in I, aVL, V5, V6
• T wave inverted in V1-V2 (secondary - normal with RBBB, not ischemia)

• QRS ≥ 120 ms
• Broad monophasic R in I, aVL, V5, V6 (no Q wave, no S wave)
• Deep QS or rS in V1
• T wave inverted in I, aVL, V5, V6 (secondary - normal with LBBB)

• RBBB: Often benign; new RBBB in acute anterior MI = proximal LAD (septal branch involvement)
• LBBB: New LBBB + chest pain = treat as STEMI (modified Sgarbossa criteria)

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LEVEL 5 - AV Blocks (Visual Patterns)

ECG 11-13: The Three AV Blocks

P----P----P----P      (every P conducts)
QRS  QRS  QRS  QRS   (every P has a QRS)
↕PR: >200ms (stretched but constant)

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P    P    P    P    P    P    P
QRS  QRS  QRS  ---  QRS  QRS  ---
PR:  ↑    ↑↑   ↑↑↑  drop  ↑    ↑↑   drop

• Benign, usually AV node level
• Common in athletes (high vagal tone) and inferior MI

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P    P    P    P    P    P
QRS  QRS  ---  QRS  QRS  ---
PR:   =    =         =    =   (CONSTANT then sudden drop)

• Dangerous - below the AV node (His-Purkinje)
• Associated with wide QRS, anterior MI
• Requires pacemaker - high risk of complete block

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P    P    P    P    P    P    P    P   (fast, ~70-80/min)
   QRS      QRS      QRS      QRS     (slow, 30-50/min)

• Narrow QRS escape = junctional (40-60/min) = AV node still working below block
• Wide QRS escape = ventricular (20-40/min) = dangerous, more hemodynamically unstable
• Emergency: atropine (narrow complex), transcutaneous pacing, urgent permanent pacemaker

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LEVEL 6 - Metabolic ECGs (Must Know for Exams)

ECG 14: Hyperkalemia - The Deadly Progression

• Peaked T waves = call for ECG immediately in any CKD/renal patient
• Sine wave = life-threatening emergency - give calcium gluconate NOW
• Treatment sequence: C-BIG-K-D (Calcium, Bicarbonate, Insulin+Glucose, Kayexalate, Dialysis)

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ECG 15: Hypokalemia - The U Wave

• Lead II (left): Flat T wave, barely visible, slight prolongation of the QT interval
• V3 (right): Prominent U wave labeled - note it is taller than the T wave in this lead

• T wave flattening → T wave inversion
• U wave prominence (U > T = significant hypokalemia)
• Apparent QT prolongation (actually QU prolongation - U wave merging with T)
• Risk: Torsades de Pointes especially if on QT-prolonging drugs

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ECG 16: Pericarditis with Cardiac Tamponade - Electrical Alternans

1. Sinus tachycardia (compensatory, filling impaired)
2. Low QRS voltage (<5 mm all limb leads and/or <10 mm chest leads) - fluid insulating the heart
3. Electrical alternans - QRS height alternates every other beat (arrows in V2, V4) - heart swinging inside fluid

• Diffuse saddle-shaped (concave) ST elevation in most leads (not just regional)
• PR segment depression (very specific for pericarditis)
• No reciprocal ST depression (except aVR)
• No Q waves

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LEVEL 7 - Clinical Syndromes (Advanced)

ECG 17: Inferior STEMI - RCA Occlusion

• ST elevation in II, III, aVF (inferior leads)
• Reciprocal ST depression in I and aVL (lateral leads)
• III > II elevation = more likely RCA (proximal)
• II > III elevation = more likely LCx

1. Right-sided leads (V3R, V4R): If ST elevation here = RV infarction (25-40% of inferior STEMIs)
   • RV MI = give fluids (not nitrates!), no diuretics, no morphine
2. Posterior leads (V7-V9) or V1-V2: Tall R + ST depression in V1-V2 = posterior extension
3. Complete AV block: RCA supplies AV node - inferior MI can cause bradycardia / heart block

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ECG 18: WPW (Wolff-Parkinson-White) Pattern

• Short PR (<120 ms) - bypassing the AV node
• Delta wave - slurred initial upstroke of QRS (most visible in lateral leads)
• Wide QRS (>120 ms) - fusion beat (normal + accessory pathway conduction)
• Pseudo-Q waves and ST-T changes - secondary to abnormal depolarization

• Orthodromic AVRT: Narrow complex tachycardia (down AV node, up AP) - treat with adenosine
• Antidromic AVRT: Wide complex tachycardia (down AP, up AV node)
• AF with WPW: Irregular wide complex tachycardia - VERY FAST rate (>250 bpm possible) → risk of VF

⚠️ Never give adenosine, digoxin, verapamil, diltiazem in AF+WPW - these block AV node but not accessory pathway, driving all conduction down the fast AP → VF Use: DC cardioversion (if unstable) or IV procainamide/ibutilide

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ECG 19: Pulmonary Embolism - S1Q3T3

1. Sinus tachycardia - most common, most sensitive
2. T-wave inversions V1-V4 - right heart strain pattern (right precordial leads)
3. New RBBB or RBBB morphology - acute RV pressure overload
4. S1Q3T3 - classic but actually uncommon (<20% of PE cases)
5. Right axis deviation
6. P pulmonale - peaked P waves from acute RA overload
7. Atrial fibrillation or flutter

• S in lead I (deep S = left lateral lead sees delayed RV activation)
• Q in lead III (inferior lead)
• T inversion in lead III (RV strain)

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ECG 20: Brugada Pattern

• Coved ST elevation ≥ 2 mm in V1 (and sometimes V2)
• Down-sloping ST segment
• T wave inversion in V1

• Risk of sudden cardiac death from VF (especially at night, during fever)
• Sodium channel mutation (SCN5A - autosomal dominant)
• Unmasked by: fever, cocaine, alcohol, flecainide, procainamide (sodium channel blockers)
• Treatment: ICD (implantable cardioverter defibrillator) for symptomatic patients
• Quinidine for recurrent VF episodes or fever-triggered events

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LEVEL 8 - Arrhythmia Recognition (Rhythm Strips)

How to Systematically Approach Any Rhythm Strip

1. RATE → Fast? Slow? Normal?
2. REGULAR? → Measure R-R intervals
3. QRS WIDTH → Narrow (<120ms) or Wide (≥120ms)?
4. P WAVES → Present? Before QRS? Normal morphology?

Arrhythmia Quick Recognition Table

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The Wide Complex Tachycardia Decision Tree

Wide Complex Tachycardia (QRS ≥120ms, Rate >100)
                    ↓
     Is patient UNSTABLE? (hypotensive, altered consciousness, pulmonary edema)
         YES ──────────────────→ SYNCHRONIZED DC CARDIOVERSION
          ↓NO
     Look for AV Dissociation?
         YES ──────────────────→ DEFINITELY VT → Amiodarone or Cardioversion
          ↓NO
     Capture beats or Fusion beats?
         YES ──────────────────→ DEFINITELY VT → Amiodarone
          ↓NO
     Brugada morphology criteria? QRS >160ms? Concordance?
         YES ──────────────────→ LIKELY VT → Amiodarone
          ↓NO
     Could this be AF + WPW? (irregular wide complex + very fast)
         YES ──────────────────→ Procainamide or Cardioversion (NOT adenosine/verapamil)
          ↓NO
     LIKELY SVT with aberrancy → Adenosine trial (have crash cart ready)

Rule: When uncertain, treat wide-complex tachycardia as VT. Adenosine is safe for narrow complex. For wide complex, amiodarone is the safest drug.

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LEVEL 9 - Special ECG Patterns (Exam Favourites)

Quick Pattern Recognition Summary

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Clinical Practice Summary Card

Every ECG you pick up, run through this checklist in 30 seconds:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
1. RATE        → Count (300 rule) / Irregular → count × 6
2. RHYTHM      → P before QRS? Regular? Sinus?
3. PR          → 120-200ms? Short (WPW)? Long (AVB)?
4. QRS         → <110ms? Wide (BBB/VT/pace)?
5. AXIS        → I and aVF upright = normal
6. ST SEGMENTS → Elevation (which leads)? Depression?
7. T WAVES     → Inverted (where)? Peaked (hyperK)?
8. QT          → Prolonged (drugs/electrolytes/long QT)?
9. P WAVES     → Peaked (RAE)? Broad (LAE)?
10. U WAVES    → Prominent (hypoK)?
11. COMPARE    → With previous ECG!
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

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