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10 Common Heart Diseases — ECG Changes & Images

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1. 🫀 ST-Elevation Myocardial Infarction (STEMI)

ECG Changes

• Hyperacute T waves — very early sign (tall, peaked, broad-based T waves)
• ST-segment elevation ≥1 mm in ≥2 contiguous limb leads or ≥2 mm in ≥2 contiguous precordial leads
• Reciprocal ST depression in mirror-image leads
• Pathological Q waves (>40 ms wide, >25% of R-wave height) — develop within hours, signify necrosis
• T-wave inversion in the evolving/chronic phase

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2. 💓 Atrial Fibrillation (AF)

ECG Changes

• Absent P waves — replaced by chaotic fibrillatory baseline (f waves, best seen in V1 and lead II)
• Irregularly irregular R-R intervals — hallmark finding
• Narrow QRS (unless aberrant conduction or bundle branch block present)
• Rapid ventricular response when rate is uncontrolled (>100 bpm = AF with RVR)
• Variable f-wave amplitude: coarse AF (amplitude >1 mm) vs fine AF

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3. 🚫 Complete (Third-Degree) Heart Block

ECG Changes

• Complete AV dissociation — P waves and QRS complexes are totally independent
• Regular P-P intervals at atrial rate (~60–100 bpm)
• Regular, slower escape R-R intervals at ventricular rate
  • Junctional escape: narrow QRS, rate ~40–60 bpm
  • Ventricular escape: wide QRS (>120 ms), rate ~20–40 bpm — indicates infra-Hisian block
• No fixed PR interval — P waves "march through" QRS and T waves
• Associated with syncope (Stokes-Adams attacks)

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4. 📈 Left Ventricular Hypertrophy (LVH)

ECG Changes

• Voltage criteria (Sokolow-Lyon): S in V1 + R in V5 or V6 ≥35 mm
• Cornell criteria: R in aVL + S in V3 >28 mm (men) or >20 mm (women)
• Left axis deviation (axis −30° to −90°)
• ST depression and T-wave inversion in lateral leads (I, aVL, V5–V6) = "strain pattern"
• Prolonged QRS (sometimes >100 ms but not full BBB)
• Left atrial enlargement (broad, bifid P wave in II, deep negative P in V1)

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5. 🩺 Acute Pericarditis

ECG Changes (4 classic stages)

• No reciprocal ST changes (unlike STEMI — except aVR)
• Spodick's sign: downsloping TP segment
• No Q waves
• Large effusion → electrical alternans (alternating QRS amplitude)

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6. 🫁 Pulmonary Embolism (PE)

ECG Changes

• Sinus tachycardia — most common finding
• S₁Q₃T₃ pattern — S wave in lead I, Q wave in lead III, inverted T wave in lead III
• Right axis deviation (axis >+90°)
• Incomplete or complete RBBB (RSR' in V1)
• T-wave inversions in V1–V4 (right ventricular strain pattern)
• P pulmonale (tall, peaked P wave >2.5 mm in lead II)
• Atrial fibrillation (can be triggered)

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7. ⚡ Ventricular Tachycardia (VT)

ECG Changes

• Wide QRS tachycardia (QRS ≥120 ms) at rate >100 bpm
• AV dissociation (P waves fire independently of QRS) — most specific finding
• Fusion beats — hybrid complex when normal sinus beat partially fuses with ectopic VT beat
• Capture beats — narrow complex amid wide tachycardia = pathognomonic
• Concordance across precordial leads:
  • Positive concordance (all positive V1–V6) → VT
  • Negative concordance (all negative) → VT
• RBBB morphology with left axis deviation or LBBB morphology with right axis deviation — favors VT over SVT with aberrancy
• Brugada algorithm (any of 4 criteria positive → VT)

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

ECG Changes (during sinus rhythm)

• Short PR interval (<120 ms) — due to bypass of AV node
• Delta wave — slurred upstroke at start of QRS (pre-excitation via accessory pathway)
• Wide QRS complex (>120 ms) — delta wave + normal QRS fused
• Secondary ST-T changes — discordant to delta wave
• Pseudo-infarct Q waves — negative delta waves in inferior leads mimicking inferior MI
• During orthodromic AVRT: narrow complex tachycardia (delta waves disappear)
• During antidromic AVRT or AF with WPW: very wide, irregular, fast (can be lethal)

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9. 🧪 Hyperkalemia

ECG Changes (progressive with rising K⁺)

• Peaked T waves most prominent in V2–V5
• No specific lead distribution (global effect)

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10. 🧬 Brugada Syndrome

ECG Changes

• Type 1 (diagnostic) — "coved" ST elevation ≥2 mm in V1–V2 (placed in 2nd, 3rd, or 4th intercostal space) descending into inverted T wave, without return to baseline
• Type 2 — "saddle-back" ST elevation with positive/biphasic T wave (not diagnostic alone)
• Incomplete RBBB morphology often present
• Fever, sodium channel blockers (ajmaline, flecainide) can unmask the pattern
• Normal baseline ECG possible — provocation testing may be required
• Associated with ventricular fibrillation and sudden cardiac death in young males, often during sleep

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Quick Reference Summary Table

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