10 Common Heart Diseases: ECG Changes & Images

1. 🫀 ST-Elevation Myocardial Infarction (STEMI)

ECG Changes

• Hyperacute T waves — earliest sign (peaked, broad T waves in affected territory)
• ST-segment elevation ≥1 mm in ≥2 contiguous limb leads or ≥2 mm in precordial leads (convex/tombstone morphology)
• Reciprocal ST depression in opposing leads
• Pathological Q waves (≥0.04 s wide, ≥25% of R wave height) — develop hours to days later
• T-wave inversion in the subacute phase

Localisation by Leads

ECG Image — Anterior STEMI (LAD occlusion)

12-lead ECG showing anterolateral STEMI: convex ST elevation in V1–V6, hyperacute T waves in V2–V4, and reciprocal ST depression in II, III, aVF. Consistent with proximal LAD occlusion.

ECG Image — Inferolateral STEMI (RCA/LCx occlusion)

ST elevations in II, III, aVF and V4–V6 (green circles), with reciprocal depression in I, aVL, V2–V3 (yellow arrows). Classic inferolateral STEMI.

2. 🫀 Atrial Fibrillation (AF)

ECG Changes

• Absent P waves — replaced by chaotic fibrillatory baseline (f-waves)
• Irregularly irregular RR intervals — hallmark finding
• Narrow QRS complexes (unless aberrant conduction or pre-existing BBB)
• Ventricular rate variable — may be rapid (AF with RVR) or slow (if AV nodal disease)
• Fibrillatory waves best seen in V1 and inferior leads

ECG Image — Atrial Fibrillation with Rapid Ventricular Response

Classic AF: no P waves, chaotic baseline, narrow irregular QRS at ~134 bpm (AF with RVR). Note poor R-wave progression suggesting possible prior anterior infarction.

ECG Image — Atrial Fibrillation (moderate rate)

Fine fibrillatory baseline (best seen in V1 and inferior leads), irregularly irregular narrow QRS at ~100 bpm.

3. 🫀 Ventricular Tachycardia (VT)

ECG Changes

• Regular wide-complex tachycardia — QRS duration >120 ms (often >140 ms)
• Heart rate typically 100–250 bpm
• AV dissociation — P waves march independently (pathognomonic)
• Fusion beats and capture beats (confirm VT)
• Positive or negative concordance across precordial leads
• Brugada, Josephson, or Vereckei criteria used to differentiate from SVT with aberrancy

ECG Image — Monomorphic Ventricular Tachycardia

Monomorphic VT: high-amplitude wide QRS at ~202 bpm, positive concordance V1–V6, superior axis (negative II, III, aVF), no visible P waves — consistent with VT in structural heart disease.

4. 🫀 Complete (Third-Degree) AV Block

ECG Changes

• Complete AV dissociation — P waves and QRS have no fixed relationship
• P waves march through at their own regular (faster) rate
• Escape rhythm — narrow QRS if junctional (40–60 bpm); wide QRS if ventricular (20–40 bpm)
• Regular RR intervals (escape rhythm is regular)
• Can follow inferior MI (usually transient, nodal block) or anterior MI (infra-Hisian, often permanent)

ECG Image — Third-Degree AV Block

12-lead ECG demonstrating total AV dissociation: atrial rate faster than ventricular rate, wide QRS escape rhythm (infra-Hisian block), T-wave inversions in I, aVL, V4–V6.

ECG Image — Third-Degree AV Block (Rhythm Strip)

Lead II rhythm strip: P waves at regular faster rate with no fixed PR interval; junctional escape beats at slow regular rate — classic third-degree block.

5. 🫀 Left Ventricular Hypertrophy (LVH)

ECG Changes

• High QRS voltage — Sokolow-Lyon: S in V1 + R in V5 or V6 ≥35 mm; Cornell: R in aVL ≥11 mm
• Left axis deviation (–30° or more negative)
• LVH strain pattern: ST depression + asymmetric T-wave inversion in lateral leads (I, aVL, V5–V6)
• Left atrial enlargement (P mitrale: bifid P wave in lead II, negative terminal P deflection in V1)
• Prolonged QRS intrinsicoid deflection in V5/V6 (>50 ms)

ECG Image — LVH with Strain Pattern

Classic LVH strain: tall R waves (V5/V6) + deep S waves (V1/V2) meeting Sokolow-Lyon criteria. Red arrows highlight ST depression and T-wave inversions in II, III, aVF, V5–V6 — typical repolarisation strain.

6. 🫀 Wolff-Parkinson-White (WPW) Syndrome

ECG Changes

• Short PR interval — <120 ms (due to accessory pathway bypassing AV node)
• Delta wave — slurred slow upstroke at onset of QRS
• Widened QRS — total duration >120 ms (due to ventricular pre-excitation)
• Secondary ST-T changes — discordant from delta wave direction
• Pathway location estimated by delta wave polarity:
  • Positive delta in V1 → left-sided pathway
  • Negative delta in II, III, aVF → posteroseptal pathway

ECG Image — WPW Syndrome

Classic WPW triad: shortened PR interval (<120 ms), delta waves in II, III, aVF and V2–V6, and widened QRS. Positive R in V1 suggests left-sided accessory pathway.

ECG Image — WPW with Pseudoinfarction Pattern

WPW: positive delta waves V1–V6 (dominant R in V1) with negative delta waves in II, III, aVF — a "pseudoinfarction" pattern typical of a left posteroseptal accessory pathway.

7. 🫀 Pulmonary Embolism (PE)

ECG Changes

• Sinus tachycardia — most common finding (>50% of cases)
• S1Q3T3 pattern — deep S in lead I + Q wave in lead III + T-wave inversion in lead III
• Right bundle branch block — complete or incomplete (rSR' in V1, wide S in V6)
• T-wave inversions in V1–V4 — right ventricular strain
• Right axis deviation
• P pulmonale (tall P wave >2.5 mm in II) — right atrial overload
• ECG is non-specific — normal in ~25% of PE cases

ECG Image — Pulmonary Embolism with S1Q3T3

Acute PE: sinus tachycardia at 116 bpm, S1Q3T3 pattern, T-wave inversions in V1–V3 and aVF, incomplete RBBB (QRS 110 ms) with persistent S in V5–V6 — all signs of right heart strain.

ECG Image — Annotated S1Q3T3 Sign

Annotated ECG: blue arrow = prominent S wave in lead I; red arrow = Q wave in lead III; yellow arrow = T-wave inversion in lead III — the classic McGinn-White (S1Q3T3) sign of acute right heart strain.

8. 🫀 Hypertrophic Cardiomyopathy (HCM)

ECG Changes

• LVH voltage criteria (common)
• Giant T-wave inversions in precordial leads (V3–V6) — classic in apical HCM (Yamaguchi variant)
• Deep narrow Q waves in I, aVL, V5–V6 (due to septal hypertrophy)
• Left axis deviation
• Left atrial enlargement (bifid P, prolonged P duration)
• ST depression in lateral leads (strain pattern)
• Arrhythmias: AF, VT common

ECG Image — Apical HCM (Yamaguchi Syndrome)

Yamaguchi-type apical HCM: giant, deep symmetric T-wave inversions in V3–V6 with high voltage (tall R in lateral leads). ST elevation V1–V2 represents septal early repolarisation. Classic for apical variant HCM.

9. 🫀 Acute Pericarditis

ECG Changes (evolve through 4 stages)

• Key differentiators from STEMI: diffuse (not regional) ST elevation, saddle-back morphology, PR depression, no reciprocal changes (except aVR)
• Spodick's sign: downsloping TP segment (highly specific)

ECG Image — Acute Pericarditis (Stage I)

Stage I pericarditis: diffuse concave ST elevation in I, II, III, aVF, V2–V6 with PR depression in lead II; reciprocal ST depression and PR elevation in aVR. Classic saddle-back morphology.

ECG Image — Pericarditis with Spodick's Sign

Diffuse concave ST elevation in limb leads and V2–V6, PR depression in lead II, Spodick's sign (downsloping TP segment), and reciprocal PR elevation in aVR.

10. 🫀 Dilated Cardiomyopathy (DCM)

ECG Changes

• Left bundle branch block (LBBB) — most characteristic; broad notched R in I/V5–V6, deep S/rS in V1
• Low QRS voltage in limb leads (<5 mm)
• Poor R-wave progression (PRWP) across precordial leads
• Non-specific ST-T changes and diffuse T-wave flattening/inversion
• Left atrial enlargement (P mitrale)
• Atrial fibrillation — very common in advanced DCM
• Ventricular ectopy / non-sustained VT

ECG Image — DCM Pattern (Low Voltage + PRWP)

DCM pattern: low voltage throughout, poor R-wave progression (pathological Q waves V1–V6), P mitrale (bifid P in II, negative terminal deflection in V1) indicating left atrial enlargement, with a PAC visible in the rhythm strip.

Quick Reference Summary Table

Clinical Pearl: ECG interpretation must always be combined with clinical context, symptoms, biomarkers, and imaging. A single ECG finding can overlap multiple diagnoses — pattern recognition improves with systematic practice using all 12 leads.