10 Heart Diseases with ECG Changes

1. 🫀 ST-Elevation Myocardial Infarction (STEMI)

ECG Changes

• Hyperacute T waves (earliest sign — tall, broad, peaked T waves)
• ST-segment elevation ≥1 mm in ≥2 contiguous limb leads, or ≥2 mm in ≥2 contiguous precordial leads
• Pathological Q waves (>40 ms wide, >25% of QRS amplitude) — develop within hours
• Reciprocal ST depression in opposing leads
• T-wave inversion in the evolutionary phase
• Localization by leads:
  • Anterior STEMI: V1–V4 (LAD occlusion)
  • Inferior STEMI: II, III, aVF (RCA or LCx)
  • Lateral STEMI: I, aVL, V5–V6
  • Posterior STEMI: tall R wave + ST depression in V1–V2

ECG Image — Anterior STEMI (LAD occlusion)

ECG Image — Inferolateral STEMI (RCA/LCx occlusion)

2. 💓 Atrial Fibrillation (AF)

ECG Changes

• Absent P waves — replaced by fibrillatory baseline (chaotic f-waves, best seen in V1 and II)
• Irregularly irregular RR intervals — the hallmark
• Narrow QRS (unless aberrant conduction/WPW)
• Rate: slow (<60 bpm), controlled (60–100 bpm), or rapid ventricular response (>100 bpm)
• Fibrillatory baseline most prominent in V1

ECG Image — Atrial Fibrillation with Rapid Ventricular Response

3. 🔴 Complete (Third-Degree) Heart Block

ECG Changes

• Complete AV dissociation — P waves and QRS complexes are independent of each other
• P waves march through QRS complexes and T waves with no fixed PR interval
• Slow ventricular escape rhythm:
  • Junctional escape: narrow QRS, rate 40–60 bpm
  • Ventricular escape: wide QRS (>120 ms), rate 20–40 bpm
• Atrial rate faster than ventricular rate
• No P-to-QRS relationship

ECG Image — Complete (Third-Degree) AV Block

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

ECG Changes

• Short PR interval (<120 ms) — early ventricular pre-excitation via accessory pathway
• Delta wave — slurred upstroke at the beginning of the QRS complex
• Widened QRS (>120 ms) due to fusion of normal conduction + accessory pathway conduction
• Secondary ST-T changes discordant to the delta wave direction
• Pseudo-infarct Q waves in inferior leads (type B WPW)
• Risk of rapid AF conducting down the accessory pathway → ventricular fibrillation

ECG Image — WPW Syndrome with Classic Delta Waves

5. 🔥 Acute Pericarditis

ECG Changes

• Diffuse, concave (saddle-shaped) ST elevation in most leads except aVR and V1
• PR segment depression in II, V4–V6 (and PR elevation in aVR) — highly specific
• No reciprocal ST depression (unlike STEMI) — key differentiator
• Spodick's sign — downward slope of the TP segment
• Temporal stages: ST elevation → T-wave flattening → T-wave inversion → normalization
• No pathological Q waves
• Sinus tachycardia common due to inflammation

ECG Image — Acute Pericarditis

6. 🌡️ Pulmonary Embolism (PE)

ECG Changes

• Sinus tachycardia — most common finding (>70% of cases)
• S1Q3T3 pattern (McGinn-White sign): prominent S wave in I, Q wave in III, T inversion in III
• Right bundle branch block (RBBB) — complete or incomplete
• T-wave inversions in V1–V4 — right ventricular strain pattern
• Right axis deviation
• P pulmonale (tall, peaked P wave >2.5 mm in II)
• New AF can occur
• Normal ECG does NOT exclude PE

ECG Image — Pulmonary Embolism with S1Q3T3 and Right Heart Strain

7. 💪 Hypertrophic Cardiomyopathy (HCM)

ECG Changes

• Left ventricular hypertrophy (LVH) voltage criteria — tall R in V5/V6 + deep S in V1 (Sokolow-Lyon >35 mm)
• Giant symmetric T-wave inversions in precordial and lateral leads (especially apical HCM/Yamaguchi syndrome — V2–V5, depth >10 mm)
• Pathological Q waves in lateral and inferior leads (due to septal hypertrophy)
• Left axis deviation
• Absence of septal Q waves in V5–V6 (loss of normal septal activation)
• ST-segment depression with strain pattern

ECG Image — HCM with Giant T-Wave Inversions (Yamaguchi/Apical HCM)

8. 🧬 Brugada Syndrome

ECG Changes

• Type 1 (diagnostic "coved" pattern):
  • ST elevation ≥2 mm in ≥1 of V1–V3 with a coved (downward sloping) morphology
  • ST descends into a negative T wave — the coved shape
• Type 2 ("saddleback" pattern) — not diagnostic alone, needs sodium channel blocker provocation
• Incomplete or complete RBBB morphology
• Changes often intermittent — may require fever, Na-channel blocker unmasking
• Risk: polymorphic VT and sudden cardiac death (especially during sleep)
• No structural heart disease

ECG Image — Brugada Syndrome Type 1 (Coved Pattern)

9. ⚡ Ventricular Tachycardia (VT)

ECG Changes

• Wide QRS tachycardia (QRS >120 ms) at rate >100 bpm (usually 140–200 bpm)
• AV dissociation — P waves independent from QRS (pathognomonic when present)
• Capture beats — occasional narrow QRS (normal sinus beat "captures" ventricles)
• Fusion beats — hybrid QRS between sinus and VT complex
• Concordance in precordial leads (all positive or all negative) — strongly suggests VT
• Northwest axis (extreme axis deviation) — common in VT
• Brugada criteria, Vereckei algorithm used for VT vs SVT with aberrancy

ECG Image — Monomorphic Ventricular Tachycardia

10. 🧪 Hyperkalemia (Cardiac Manifestations)

ECG Changes — Progressive with Rising K⁺

ECG Image — Progressive Hyperkalemia Changes (Harrison's Internal Medicine)

ECG Image — Severe Hyperkalemia Before and After Treatment

Quick Reference Summary Table

Clinical note: ECG interpretation must always be correlated with the clinical presentation, history, and other investigations. This overview is for educational purposes. The ECG images are sourced from peer-reviewed clinical databases and Harrison's Principles of Internal Medicine.