10 Common Heart Diseases: ECG Changes & Images

1. ST-Elevation Myocardial Infarction (STEMI)

ECG Changes:

• Hyperacute T waves (earliest sign — peaked, broad, symmetric)
• ST-segment elevation ≥1 mm in ≥2 contiguous limb leads, or ≥2 mm in ≥2 contiguous precordial leads (convex/tombstone morphology)
• Reciprocal ST depression in opposing leads
• Pathological Q waves (>40 ms wide, >1/4 QRS amplitude) — develop over hours
• T-wave inversion (later stage)
• Localization by leads:
  • Anterior (LAD): V1–V4
  • Inferior (RCA): II, III, aVF
  • Lateral (LCx): I, aVL, V5–V6

ECG Images:

Anterior STEMI (LAD occlusion):

Inferolateral STEMI:

2. Atrial Fibrillation (AFib)

ECG Changes:

• Absent P waves — replaced by chaotic fibrillatory baseline (most visible in V1)
• Irregularly irregular R-R intervals (hallmark finding)
• Narrow QRS complexes (unless aberrant conduction/bundle branch block)
• Ventricular rate may be slow, normal, or rapid (RVR >100 bpm)
• No organized atrial activity

ECG Image:

3. Ventricular Tachycardia (VT)

ECG Changes:

• Wide QRS complexes (>120 ms) — hallmark
• Regular, rapid rate (100–250 bpm)
• AV dissociation (P waves independent of QRS) — highly specific for VT
• Fusion beats and capture beats (pathognomonic when seen)
• Concordance in precordial leads (all positive or all negative)
• Northwest axis (extreme right axis deviation)
• No visible P waves preceding QRS

ECG Images:

4. Complete (Third-Degree) Heart Block

ECG Changes:

• Complete AV dissociation — P waves and QRS complexes march independently
• Atrial rate faster than ventricular rate
• No fixed PR interval — P waves "march through" QRS and T waves
• Escape rhythm: Narrow QRS if junctional origin (~40–60 bpm); Wide QRS if ventricular origin (~20–40 bpm)
• Regular R-R intervals and regular P-P intervals (each independent)

ECG Images:

5. Wolff-Parkinson-White (WPW) Syndrome

ECG Changes (Classic Triad):

• Short PR interval (<120 ms)
• Delta wave — slurred upstroke at the start of QRS (slow initial ventricular depolarization via accessory pathway)
• Widened QRS (>120 ms total due to delta wave + normal conduction fusion)
• Secondary ST-T wave changes (discordant to delta wave direction)
• Pseudo-infarction Q waves in inferior leads (negative delta waves mimicking Q waves)
• Pathway localization possible from delta wave polarity

ECG Images:

6. Acute Pericarditis

ECG Changes (Stage I — acute):

• Diffuse, concave ("saddle-shaped") ST elevation in almost all leads (I, II, aVF, V2–V6) — not confined to one vascular territory
• PR-segment depression in the same leads (atrial injury) — most visible in lead II
• Reciprocal ST depression and PR elevation in aVR (highly specific)
• Spodick's sign — downsloping TP segment
• Later stages: ST normalizes → T-wave inversion → resolution

Key Differentiator from STEMI:

• Pericarditis: saddle-shaped, diffuse, no reciprocal ST depression (except aVR), PR depression
• STEMI: convex ST elevation, localized, reciprocal depression in opposing leads

ECG Images:

7. Pulmonary Embolism (PE)

ECG Changes:

• Sinus tachycardia — most common finding (>75% of cases)
• S1Q3T3 pattern (McGinn-White sign): prominent S wave in lead I + Q wave in lead III + inverted T wave in lead III
• T-wave inversions in V1–V4 (right ventricular strain)
• Incomplete or complete RBBB (right ventricular overload)
• Right axis deviation
• P pulmonale (peaked P waves in II — right atrial strain)
• Atrial fibrillation may occur
• ECG may be completely normal in up to 25% of cases

ECG Images:

8. Left Ventricular Hypertrophy (LVH)

ECG Changes:

• Voltage criteria:
  • Sokolow-Lyon: S in V1 + R in V5 or V6 ≥35 mm
  • Cornell: R in aVL + S in V3 >28 mm (men) or >20 mm (women)
  • R in aVL ≥12 mm
• LVH strain pattern: ST depression + T-wave inversion in lateral leads (I, aVL, V5–V6) — discordant to QRS
• Left axis deviation
• Prolonged QRS duration (but usually <120 ms)
• Left atrial enlargement (broad, notched P wave — "P mitrale")

ECG Image:

9. Hypertrophic Cardiomyopathy (HCM)

ECG Changes:

• LVH voltage criteria (tall R waves V4–V6, deep S waves V1–V2)
• Deep, narrow Q waves in lateral leads (I, aVL, V5–V6) — due to septal hypertrophy (initial septal depolarization away from lateral leads); can mimic inferior MI
• Giant T-wave inversions (especially in apical variant / Yamaguchi): deeply inverted T waves V3–V6, often >10 mm
• ST-segment depression in lateral leads (strain pattern)
• Left axis deviation
• ECG abnormal in ~90% of HCM patients

ECG Images:

10. Brugada Syndrome

ECG Changes (Type 1 — Diagnostic):

• Coved-type ST elevation ≥2 mm in V1 (±V2) with a high take-off, descending slope merging into an inverted T wave without isoelectric interval
• Pseudo-RBBB pattern in V1–V2
• Changes most visible when leads placed at higher intercostal spaces (2nd–3rd ICS)
• Types 2 & 3: "saddle-back" or minimal ST elevation — not diagnostic alone
• Unmask with fever, sodium channel blockers (ajmaline, flecainide challenge)

ECG Images:

Quick Reference Summary Table

Note: ECG interpretation always requires clinical correlation. A "normal" ECG does not exclude serious heart disease (e.g., PE can be normal in 25% of cases). When findings are ambiguous, serial ECGs and additional testing (echocardiogram, troponins, CT-PA, cardiac MRI) are essential.The guide covers all 10 diseases with clinical ECG images sourced from peer-reviewed medical literature. Here's a recap of what was covered:

1. STEMI — Convex ST elevation localized to coronary territory + reciprocal changes
2. Atrial Fibrillation — No P waves + irregularly irregular rhythm
3. Ventricular Tachycardia — Wide QRS tachycardia + AV dissociation
4. Complete Heart Block — AV dissociation with independent atrial/ventricular rhythms
5. WPW Syndrome — Short PR + delta wave + widened QRS triad
6. Acute Pericarditis — Diffuse saddle-shaped ST elevation + PR depression (vs STEMI key differentiator)
7. Pulmonary Embolism — Sinus tachycardia + S1Q3T3 + right ventricular strain pattern
8. LVH — High voltage + lateral strain pattern (ST depression + T inversion)
9. Hypertrophic CMP — Giant T-wave inversions + deep lateral Q waves
10. Brugada Syndrome — Coved ST elevation ≥2 mm in V1–V2 with inverted T wave