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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 (earliest sign — tall, peaked, broad-based)
• ST-segment elevation ≥1 mm in ≥2 contiguous limb leads or ≥2 mm in precordial leads (convex/tombstone morphology)
• Reciprocal ST depression in opposite leads
• Pathological Q waves develop within hours (necrosis marker)
• T-wave inversion in evolving phase

Localization by Leads

ECG Image — Anterior STEMI (LAD occlusion)

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2. ❤️ Atrial Fibrillation (AF)

ECG Changes

• Absent P waves — replaced by chaotic fibrillatory (f) waves, best seen in V1 and lead II
• Irregularly irregular RR intervals (hallmark)
• Narrow QRS complexes (unless aberrant conduction or pre-excitation)
• Rate: can be slow (<60 bpm), controlled (60–100 bpm), or rapid (>100 bpm = AF with rapid ventricular response)
• f-wave frequency: 350–600 impulses/min

ECG Image — Atrial Fibrillation with rapid ventricular response

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3. 🔴 Complete (Third-Degree) Heart Block

ECG Changes

• Complete AV dissociation — P waves and QRS complexes march independently
• Atrial rate > ventricular rate
• Regular PP intervals and regular RR intervals, but no fixed PR relationship
• Escape rhythm:
  • Junctional (narrow QRS, rate 40–60 bpm) — block at AV node
  • Ventricular (wide QRS >120ms, rate 20–40 bpm) — block below His bundle
• P waves may be buried in QRS or T waves

ECG Image — Third-Degree (Complete) AV Block

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4. 💛 Acute Pericarditis

ECG Changes (4 stages)

• Stage 1 (acute): Diffuse concave/saddle-shaped ST elevation in most leads (except aVR & V1); PR-segment depression (most specific sign); Spodick's sign (downsloping TP segment)
• Stage 2: ST normalizes; PR depression persists
• Stage 3: Diffuse T-wave inversions
• Stage 4: Return to normal

Key differentiator from STEMI: ST elevation is diffuse (not territory-limited), concave (not convex), and PR depression is present

ECG Image — Acute Pericarditis

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5. 🫁 Pulmonary Embolism (PE)

ECG Changes

• Sinus tachycardia (most common — seen in ~40% of cases)
• S1Q3T3 pattern (classic but only ~20% sensitive):
  • Prominent S wave in lead I
  • Q wave in lead III
  • Inverted T wave in lead III
• Right axis deviation
• Right bundle branch block (complete or incomplete)
• T-wave inversions in V1–V4 (right ventricular strain)
• P pulmonale (peaked P waves — right atrial overload)
• New AF may occur

ECG Image — Pulmonary Embolism with S1Q3T3

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

ECG Changes (sinus rhythm / pre-excitation pattern)

• Short PR interval (<120 ms) — early ventricular activation via accessory pathway
• Delta wave — slurred upstroke at start of QRS (partial pre-excitation)
• Wide QRS complex (>120 ms total)
• Discordant ST-T changes (secondary to abnormal depolarization)
• Pseudo Q waves in inferior leads (mimics inferior MI)
• SVT/AVRT during tachycardia: typically narrow complex (orthodromic); wide complex if antidromic or in AF

ECG Image — WPW Syndrome with delta waves

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7. 🟠 Ventricular Tachycardia (VT)

ECG Changes

• Rate: 100–250 bpm
• Wide QRS complexes (>120 ms, often >140 ms)
• Regular rhythm (monomorphic VT) or irregular (polymorphic/TdP)
• AV dissociation (P waves independent of QRS — pathognomonic when visible)
• Fusion beats and capture beats (confirm VT)
• Concordance: all precordial leads positive or all negative → ventricular origin
• Axis: extreme right axis deviation ("northwest axis") common

Brugada criteria distinguish VT from SVT-with-aberrancy

ECG Image — Monomorphic Ventricular Tachycardia

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8. 🟡 Left Ventricular Hypertrophy (LVH)

ECG Changes

• Voltage criteria (most specific: Cornell, Sokolow-Lyon):
  • Sokolow-Lyon: S in V1 + R in V5 or V6 ≥35 mm
  • Cornell: R in aVL + S in V3 >28 mm (men), >20 mm (women)
  • R in aVL ≥12 mm alone
• LV strain pattern: ST depression + asymmetric T-wave inversion in lateral leads (I, aVL, V5–V6)
• Left axis deviation
• Prolonged QRS duration
• Left atrial enlargement (P mitrale: broad notched P in II, deep biphasic P in V1)

ECG Image — LVH with Strain Pattern

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9. 🔵 Hypertrophic Cardiomyopathy (HCM)

ECG Changes

• LVH voltage criteria (high amplitude QRS in precordial leads)
• Giant deep T-wave inversions in precordial leads (especially V2–V5) — most striking in apical HCM (Yamaguchi syndrome), can reach >10 mm
• Abnormal Q waves in lateral and inferior leads (septal hypertrophy)
• Left axis deviation
• ST-segment depression in lateral leads
• AF — common complication (~20% of patients)
• P-wave abnormalities (left atrial enlargement)
• High risk for sudden death — arrhythmias may be first presentation

ECG Image — Apical HCM with Giant T-wave Inversions

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10. 🟤 Dilated Cardiomyopathy (DCM)

ECG Changes

• Left bundle branch block (LBBB) — most common pattern:
  • Wide QRS ≥120 ms
  • Broad monophasic R in I, aVL, V5–V6
  • rS or QS in V1–V3
  • Discordant ST-T changes
• Poor R-wave progression (V1–V4 — reflecting anterior wall thinning/fibrosis)
• Non-specific intraventricular conduction delay (IVCD)
• Atrial fibrillation (common due to atrial dilation)
• Pathological Q waves (mimicking prior MI — due to fibrosis)
• PVCs and non-sustained VT (common, ↑ SCD risk)
• Low voltage (if large pericardial effusion co-exists)

ECG Image — DCM with LBBB

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Quick Reference Summary Table

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