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10 Common Heart Diseases: ECG Changes & Images

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1. 🫀 Acute Myocardial Infarction (STEMI) — Anterior

ECG Changes:

• Hyperacute T waves (earliest sign — tall, peaked, broad-based)
• ST-segment elevation ≥1 mm in ≥2 contiguous leads (convex "tombstone" morphology)
• Pathological Q waves (>40 ms wide, >25% of QRS height) — indicate necrosis
• Reciprocal ST depression in opposing leads
• T-wave inversion in later stages
• Lead distribution: V1–V4 (anterior/LAD territory), V5–V6 + I + aVL (anterolateral), II/III/aVF (inferior/RCA or LCx)

Anatomical Correlation:

ECG Image — Anterolateral STEMI:

ECG Image — Inferior STEMI (with posterior involvement):

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2. ❤️‍🩹 Atrial Fibrillation (AF)

ECG Changes:

• No visible P waves — replaced by chaotic fibrillatory (f) waves, best seen in V1 and II
• Irregularly irregular R-R intervals (hallmark sign)
• Narrow QRS (unless aberrant conduction/bundle branch block)
• Ventricular rate: uncontrolled (>100 bpm), controlled (60–100), or bradycardic (<60)
• Fine vs. coarse AF: coarse f-waves can mimic atrial flutter

ECG Image — Atrial Fibrillation (fast ventricular response):

ECG Image — Coarse AF:

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3. 🛑 Complete (Third-Degree) AV Block

ECG Changes:

• Complete AV dissociation — P waves and QRS complexes are completely independent
• P waves occur at a faster regular rate (atrial rate)
• QRS complexes occur at a slower, regular escape rate (ventricular rate)
• Wide QRS (>120 ms) if escape rhythm is ventricular (infra-Hisian); narrow QRS if junctional escape
• No fixed PR interval — P waves "march through" QRS complexes
• Typically presents with bradycardia (ventricular rate 30–45 bpm)

ECG Image — Complete (3rd Degree) AV Block:

ECG Image — 3rd Degree Block (junctional escape, narrow QRS):

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4. ⚡ Ventricular Tachycardia (VT)

ECG Changes:

• Wide QRS (>120 ms) at rate >100 bpm
• Monomorphic VT: uniform QRS morphology, regular rhythm
• AV dissociation (P waves unrelated to QRS) — pathognomonic when seen
• Fusion beats and capture beats (Dressler beats) — confirm ventricular origin
• Concordance: all precordial leads positive (positive) or negative (negative) — strongly suggests VT
• Northwest axis (extreme left axis deviation)
• Rate typically 140–220 bpm

ECG Image — Monomorphic VT (wide complex tachycardia):

ECG Image — Wide Complex Tachycardia (VT):

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5. 🫁 Pulmonary Embolism (PE)

ECG Changes:

• Sinus tachycardia — most common finding (>50% of cases)
• Classic S1Q3T3 pattern: deep S in I, Q wave in III, T-wave inversion in III
• Right bundle branch block (RBBB) — complete or incomplete
• T-wave inversions in V1–V4 (right ventricular strain)
• Right axis deviation
• P pulmonale (tall peaked P waves in II if right atrial strain)
• New atrial fibrillation

ECG Image — PE with S1Q3T3 (annotated):

ECG Image — PE with RV strain (RBBB + precordial T-wave inversions):

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6. 💉 Left Ventricular Hypertrophy (LVH)

ECG Changes:

• Sokolow-Lyon: S in V1 + R in V5 or V6 ≥35 mm
• Cornell voltage: R in aVL + S in V3 >28 mm (men) or >20 mm (women)
• Cornell product: >2440 mm·ms

• ST depression + T-wave inversion in lateral leads (I, aVL, V5–V6) — "strain pattern"
• Left axis deviation
• Left atrial enlargement (broad/notched P waves, negative terminal component in V1)

ECG Image — LVH with Cornell voltage criteria:

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7. 🔥 Acute Pericarditis

ECG Changes (classically evolve in 4 stages):

• Stage I: Diffuse, concave (saddle-shaped) ST elevation in most leads (except aVR and V1); PR depression (most specific finding); reciprocal changes in aVR (ST depression + PR elevation)
• Stage II: ST returns to baseline, T waves flatten
• Stage III: T-wave inversions develop diffusely
• Stage IV: Normalization (weeks to months)
• Spodick's sign: downsloping TP segment (early and specific)
• Key differentiator from STEMI: diffuse (not territorial) + concave morphology + PR depression

ECG Image — Acute Pericarditis (diffuse saddle ST + PR depression):

ECG Image — Pericarditis with Spodick's sign:

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8. ⚡ Wolff-Parkinson-White Syndrome (WPW)

ECG Changes:

• Short PR interval (<120 ms) — accessory pathway bypasses AV node delay
• Delta wave — slurred upstroke at start of QRS (initial ventricular pre-excitation)
• Wide QRS (>120 ms) — due to fusion of pre-excited and normally conducted depolarization
• Pseudo-infarct Q waves (negative delta waves in inferior or lateral leads can mimic MI)
• Secondary ST-T changes discordant to QRS direction
• Accessory pathway localization based on delta wave polarity in each lead

Risk: WPW + AF → rapid conduction via accessory pathway → ventricular fibrillation

ECG Image — WPW (classic delta waves + short PR):

ECG Image — WPW (posteroseptal pathway, pseudoinfarct Q waves inferior):

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9. 🧂 Hyperkalemia

ECG Changes (progressive with rising K⁺):

ECG Image — Severe Hyperkalemia (peaked T waves + wide QRS + sine wave):

ECG Image — Early-Moderate Hyperkalemia (peaked T waves):

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10. 🫀 Dilated Cardiomyopathy (DCM)

ECG Changes:

• Left Bundle Branch Block (LBBB): broad notched R waves in I, aVL, V5–V6; deep S waves in V1; QRS >120 ms; secondary ST-T changes discordant to QRS
• Poor R wave progression (V1–V4) — mimics anterior infarction
• Left axis deviation
• Left atrial enlargement — broad, bifid P waves (P mitrale)
• Sinus tachycardia (compensatory)
• Non-specific intraventricular conduction delay (IVCD)
• Ventricular ectopy / premature ventricular complexes (PVCs)
• Low voltage (if coexisting pericardial effusion)

ECG Image — DCM with LBBB:

ECG Image — DCM (echocardiogram + LBBB ECG):

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Quick Reference Summary Table

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Clinical Pearl: Always interpret ECG findings in clinical context. Many findings overlap (e.g., LBBB can obscure STEMI — use Sgarbossa criteria; WPW can mimic STEMI or AF).