10 Common Heart Diseases: ECG Changes & Images

1. ST-Elevation Myocardial Infarction (STEMI)

What it is

ECG Changes

• Hyperacute T-waves - the earliest sign; tall, broad, symmetrical T-waves before ST elevation
• ST elevation ≥1 mm in ≥2 contiguous limb leads, or ≥2 mm in ≥2 contiguous precordial leads
• Reciprocal ST depression in opposite leads (e.g., ST elevation in II, III, aVF with reciprocal depression in I, aVL for inferior STEMI)
• Pathological Q waves develop within hours - indicate transmural necrosis (>40 ms wide, >25% of R wave height)
• T-wave inversion after the acute phase
• Lead localisation:
  • Anterior: V1-V4 (LAD occlusion)
  • Inferior: II, III, aVF (RCA or LCx)
  • Lateral: I, aVL, V5-V6 (LCx)
  • Posterior: ST depression V1-V3 with dominant R waves (mirror image)

ECG Image - Anterior-Lateral STEMI

2. Atrial Fibrillation (AF)

What it is

ECG Changes

• Absent P waves - replaced by fibrillatory (f) waves: irregular, low-amplitude baseline undulations
• Irregularly irregular R-R intervals - the hallmark finding
• Ventricular rate varies (typically 100-180 bpm if uncontrolled; <60 bpm if over-rate-controlled)
• Narrow QRS (unless aberrant conduction or pre-existing bundle branch block)
• Coarse AF - large f-waves (often seen with rheumatic mitral disease)
• Fine AF - small f-waves (common in ischaemic/hypertensive disease)

ECG Image

3. Atrial Flutter

What it is

ECG Changes

• Sawtooth flutter waves at ~300 bpm - best seen in II, III, aVF (negative/inverted sawtooth) and V1 (positive)
• Regular R-R intervals with fixed AV block ratio: most commonly 2:1 (ventricular rate ~150 bpm), 3:1, or 4:1
• No true isoelectric baseline between flutter waves
• Narrow QRS (unless aberrant conduction)
• Classic clue: regular tachycardia at exactly 150 bpm = flutter with 2:1 block until proven otherwise

4. Complete (Third-Degree) Heart Block

What it is

ECG Changes

• P waves and QRS complexes are completely independent (AV dissociation)
• P-wave rate > QRS rate (e.g., P at 80/min, QRS at 35/min)
• No constant PR interval - PR interval varies randomly
• Escape rhythm determines QRS morphology:
  • Junctional escape: narrow QRS, rate 40-60/min
  • Ventricular escape: wide, bizarre QRS, rate 20-40/min
• Regular P-P intervals and regular (but slow) R-R intervals - both are regular but completely independent

5. Left Bundle Branch Block (LBBB)

What it is

ECG Changes (using the WiLLiaM MaRRoW mnemonic)

• QRS duration ≥120 ms (broad QRS)
• Broad, notched ("M-shaped") R wave in lateral leads I, aVL, V5, V6 - the "W" pattern
• Deep S wave (or rS pattern/QS) in V1 - the "M" pattern in right leads
• No septal Q waves in leads I, V5, V6 (normally present)
• Discordant ST-T changes: ST depression and T-wave inversion in leads with dominant R waves (I, V5, V6); ST elevation in leads with deep S waves (V1-V3)
• Left axis deviation common
• New LBBB in context of chest pain = STEMI equivalent - apply Sgarbossa criteria

ECG Image

6. Right Bundle Branch Block (RBBB)

What it is

ECG Changes (using the WiLLiaM MaRRoW mnemonic)

• QRS duration ≥120 ms
• RSR' ("rabbit ears" or M-shaped) pattern in V1 - the dominant terminal R' in V1
• Wide S wave in lateral leads I, V5, V6 - deep, slurred terminal S wave
• ST depression and T-wave inversion in V1-V3 (appropriate discordance)
• Right axis deviation common
• Incomplete RBBB: same morphology with QRS 100-120 ms

7. Left Ventricular Hypertrophy (LVH)

What it is

ECG Changes

• Increased QRS voltage - the primary finding:
  • 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)
  • R in aVL ≥11-12 mm
• Left axis deviation
• LV strain pattern: ST depression + T-wave inversion in lateral leads (I, aVL, V4-V6)
• Prolonged QRS (not >120 ms, but approaching)
• Left atrial enlargement pattern: P mitrale (broad, notched P in II; biphasic P in V1)

8. Wolff-Parkinson-White (WPW) Syndrome

What it is

ECG Changes

• Short PR interval (<120 ms) - due to bypass of AV node delay
• Delta wave - slurred upstroke at the start of the QRS (pre-excitation of ventricle via accessory pathway)
• Widened QRS (≥120 ms) - combination of delta wave + normal conduction
• Secondary ST-T changes - discordant to QRS direction
• Type A: dominant R wave in V1 (left-sided pathway)
• Type B: negative delta wave/QS in V1 (right-sided pathway)
• AF in WPW: chaotic wide-complex tachycardia with varying QRS morphology - life-threatening (can degenerate to VF)
• The HCM ECG shown below is from LITFL and demonstrates deep, widespread T-wave inversions:

9. Hypertrophic Cardiomyopathy (HCM)

What it is

ECG Changes

• LVH voltage criteria in most patients (tall R waves, deep S waves)
• Deep, widespread T-wave inversions - especially striking in lateral and inferior leads; can be giant in apical HCM (Yamaguchi syndrome)
• Asymmetric septal Q waves: deep, narrow ("dagger") Q waves in lateral (I, aVL, V5-V6) and inferior leads - caused by septal hypertrophy
• Left atrial enlargement pattern
• Left axis deviation
• Apical HCM: massive T-wave inversions V1-V6 with high voltage
• 5% of HCM patients have a normal ECG

10. Acute Pericarditis

What it is

ECG Changes (four stages)

• ST elevation is diffuse (not in a coronary territory)
• Concave/saddle-shaped ST elevation (vs. convex in STEMI)
• PR depression present (pathognomonic for pericarditis)
• No reciprocal ST depression except aVR and V1
• No pathological Q waves
• Spodick's sign: downsloping TP segment (best seen in II)

Summary Table

• Braunwald's Heart Disease, Textbook of Cardiovascular Medicine (Braunwald's Heart Disease, 2 Vol Set)
• Tintinalli's Emergency Medicine: A Comprehensive Study Guide
• Goldman-Cecil Medicine International Edition
• LITFL ECG Library - Life in the Fast Lane
• ECGwaves.com - Clinical ECG Interpretation
• ECG Guru

Clinical Note: ECG interpretation always requires clinical context. These ECG patterns are diagnostic aids - never substitute for a complete clinical assessment. Some conditions (e.g., posterior STEMI, STEMI with LBBB) can be easily missed and require high clinical suspicion.Here's a quick recap of what was covered:

1. STEMI - Hyperacute T-waves, ST elevation in a coronary territory, reciprocal depression, Q waves
2. Atrial Fibrillation - Absent P waves, irregularly irregular QRS
3. Atrial Flutter - Sawtooth flutter waves at ~300/min, 2:1 or 3:1 ventricular response
4. Complete Heart Block - Full P-QRS dissociation, slow escape rhythm
5. Left Bundle Branch Block (LBBB) - Wide QRS, M-shaped R in lateral leads, rS in V1
6. Right Bundle Branch Block (RBBB) - Wide QRS, RSR' ("rabbit ears") in V1, broad S in I/V6
7. Left Ventricular Hypertrophy (LVH) - Tall voltage, left axis, lateral strain pattern
8. Wolff-Parkinson-White (WPW) - Short PR, delta wave, wide QRS
9. Hypertrophic Cardiomyopathy (HCM) - LVH voltage, septal Q waves, giant T-wave inversions
10. Acute Pericarditis - Diffuse concave ST elevation, PR depression, no Q waves