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Explain me 10 common heart disease with ecg changes and ecg images of those diseases

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10 common heart diseases ECG changes electrocardiogram findings with images

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I now have comprehensive textbook content and ECG images from Harrison's Principles of Internal Medicine, Ganong's Physiology, and Guyton & Hall. Here is the full, detailed answer:

10 Common Heart Diseases: ECG Changes and Images

1. ST-Elevation Myocardial Infarction (STEMI)

Mechanism: Total occlusion of a coronary artery causes transmural ischemia. The current of injury shifts the ST vector toward the outer (epicardial) layers.
ECG Changes:
  • Hyperacute T waves - tall, broad, peaked T waves in the first minutes
  • ST elevation ≥ 1 mm in ≥2 contiguous leads (the "tombstone" pattern in severe cases)
  • Reciprocal ST depression in opposite leads
  • Q wave formation within hours to days (indicating irreversible necrosis)
  • T wave inversion as the infarct evolves
Localization:
  • Anterior STEMI: ST elevation in V1-V6, I, aVL (LAD occlusion)
  • Inferior STEMI: ST elevation in II, III, aVF with reciprocal depression in I, aVL (RCA or LCx occlusion)
  • Posterior: Reciprocal ST depressions in V1-V3
ECG - Anterior STEMI (Acute and Evolving):
Anterior STEMI ECG sequence showing acute and evolving changes in leads I, II, III, aVR, aVL, aVF, V2, V4, V6
Acute (top row) and evolving (bottom row) anterior ST-elevation/Q-wave infarction. Note ST elevation with developing Q waves. - Harrison's Principles of Internal Medicine 22E
ECG - Inferior STEMI (Acute and Evolving):
Inferior STEMI ECG sequence
Acute (top) and evolving (bottom) inferior ST-elevation/Q-wave infarction. ST elevation in II, III, aVF with reciprocal depressions in anterior leads. - Harrison's Principles of Internal Medicine 22E
Ischemia diagram:
Current of injury diagram showing subendocardial vs transmural ischemia ST changes
A = Subendocardial ischemia causing ST depression; B = Transmural ischemia causing ST elevation. - Harrison's Principles of Internal Medicine 22E

2. Non-ST-Elevation Myocardial Infarction (NSTEMI) / Unstable Angina

Mechanism: Partial occlusion or severe subendocardial ischemia. The ST vector shifts toward the subendocardium.
ECG Changes:
  • ST depression (often horizontal or downsloping) in precordial leads, often V1-V5
  • T wave inversions - can be diffuse or regional
  • No pathological Q waves (by definition, though may appear later)
  • Wellens' sign - deep symmetric T-wave inversions in V1-V4 indicating critical LAD stenosis (a "pre-infarction" pattern)
ECG - Anterior wall ischemia / Wellens' T waves:
Anterior ischemia with deep T wave inversions V1-V6 - Wellens sign
Severe anterior wall ischemia causing prominent T-wave inversions in precordial leads V1-V6 (Wellens T-wave sign) - associated with high-grade LAD stenosis. - Harrison's Principles of Internal Medicine 22E

3. Atrial Fibrillation (AF)

Mechanism: Chaotic, disorganized electrical activity in the atria with no coordinated depolarization. Multiple re-entrant wavelets depolarize the atria randomly.
ECG Changes:
  • Absent P waves - replaced by irregular fibrillatory baseline (f waves, 350-600 bpm)
  • Irregularly irregular RR intervals - the hallmark finding
  • Narrow QRS (unless aberrant conduction or pre-existing BBB)
  • Ventricular rate typically 100-180 bpm if uncontrolled
ECG - Atrial Fibrillation (Lead II):
Atrial fibrillation ECG in lead II showing irregular rhythm, no P waves
Atrial fibrillation in Lead II. No visible P waves; the QRS complexes are normal in morphology but are irregularly spaced - the defining feature of AF. - Guyton & Hall Textbook of Medical Physiology

4. First-Degree AV Block

Mechanism: Slowing of conduction through the AV node. Every impulse is still conducted but takes longer.
ECG Changes:
  • Prolonged PR interval > 200 ms (0.20 s) on every beat
  • Normal P wave morphology
  • Normal QRS after every P wave (1:1 conduction maintained)
  • Regular rhythm
ECG - First-Degree Heart Block:
First degree heart block ECG showing prolonged PR interval of 0.38 seconds
First-degree heart block with PR interval = 0.38 s. Every P wave conducts but with abnormal delay. - Ganong's Review of Medical Physiology

5. Second-Degree AV Block (Mobitz Type I - Wenckebach)

Mechanism: Progressively increasing AV node fatigue until one impulse fails to conduct, then the cycle resets.
ECG Changes:
  • Progressively lengthening PR interval with each beat
  • Dropped QRS (non-conducted P wave) after the longest PR interval
  • The PR interval is shortest immediately after the dropped beat
  • Group beating pattern
ECG - Second-Degree Heart Block (Wenckebach):
Second degree heart block Wenckebach phenomenon ECG - progressive PR lengthening then dropped beat
Second-degree AV block (Wenckebach phenomenon) in lead aVF. P waves (labeled P) are followed by QRS complexes with progressively lengthening intervals, then a dropped beat. - Ganong's Review of Medical Physiology

6. Complete (Third-Degree) AV Block

Mechanism: Total interruption of conduction between atria and ventricles. The atria and ventricles beat independently from separate pacemakers.
ECG Changes:
  • Complete AV dissociation - P waves and QRS complexes are completely independent
  • P waves march through at a faster rate (60-100 bpm)
  • Slow escape rhythm drives the ventricles:
    • Junctional escape: rate 40-60 bpm, narrow QRS
    • Ventricular escape: rate 20-40 bpm, wide QRS
  • PP intervals and RR intervals are each regular, but bear no relationship to each other
ECG - Complete Heart Block:
Complete heart block ECG showing independent P waves at rate 107 and QRS complexes at rate 43
Complete heart block: atrial rate 107 bpm, ventricular rate 43 bpm. P waves and QRS complexes march independently with no relationship. - Ganong's Review of Medical Physiology

7. Left Bundle Branch Block (LBBB)

Mechanism: Block in the left bundle branch causes late, abnormal activation of the left ventricle - depolarization spreads from right to left through myocardium rather than the specialized conduction system.
ECG Changes:
  • Wide QRS ≥ 120 ms (≥3 small squares)
  • Broad, notched R wave ("M-shaped") in lateral leads I, aVL, V5, V6
  • Deep S wave (or QS pattern) in V1
  • No septal Q waves in lateral leads (loss of normal left-to-right septal activation)
  • Secondary ST-T changes - ST and T are discordant (opposite polarity) to the main QRS deflection
  • Left axis deviation common
ECG - Left Bundle Branch Block (V5 and V6):
Left bundle branch block ECG in leads V5 and V6 showing broad R waves with ST depression and T wave inversion
LBBB in leads V5 and V6: broad notched R waves with discordant (downward) ST-T changes - classic secondary repolarization abnormality. - Ganong's Review of Medical Physiology
Clinical note: New LBBB in a patient with chest pain should be treated as a STEMI equivalent until proven otherwise.

8. Left Ventricular Hypertrophy (LVH)

Mechanism: Increased muscle mass (typically from chronic hypertension, aortic stenosis, or hypertrophic cardiomyopathy) generates larger electrical forces directed leftward and posteriorly.
ECG Changes:
  • High-voltage QRS: Classic Sokolow-Lyon criteria: SV1 + RV5 or RV6 > 35 mm
  • Left axis deviation
  • ST depression and T wave inversions in I, aVL, V5-V6 (the "strain" pattern) - due to repolarization abnormality
  • Left atrial abnormality frequently co-exists (broad, notched P wave)
  • Slow R-wave progression in precordial leads possible
  • Sensitivity of voltage criteria is moderate; echo is more definitive
Key ECG criteria from Harrison's: RaVL >20 mm (women) or >28 mm (men) is a particularly useful criterion. ST depression with T-wave inversion in leads with prominent R waves constitutes the "strain" pattern and indicates a more severe degree of hypertrophy.

9. Pulmonary Embolism (Acute Cor Pulmonale)

Mechanism: Massive PE causes acute right ventricular pressure overload and dilation. This shifts the cardiac electrical axis rightward and causes right ventricular strain.
ECG Changes:
  • Sinus tachycardia - the most common and often the only finding
  • S1Q3T3 pattern - S wave in lead I, Q wave in lead III, T-wave inversion in lead III
  • Right axis deviation
  • Right bundle branch block (complete or incomplete) - due to acute RV strain
  • ST depression and T-wave inversions in right precordial leads V1-V4 (simulating anterior ischemia)
  • Atrial fibrillation or flutter may occur
  • Normal ECG does not exclude PE
Harrison's note: "Acute right ventricular dilation may be associated with slow R-wave progression and ST-T abnormalities in V1-V4 simulating acute anterior infarction."

10. Hypertrophic Cardiomyopathy (HCM)

Mechanism: Asymmetric septal hypertrophy with myocardial fiber disarray leads to abnormal depolarization and repolarization patterns. Elevated LV pressures cause LVH-like changes.
ECG Changes:
  • Left ventricular hypertrophy with high-voltage QRS
  • Abnormal Q waves in lateral leads (I, aVL, V5-V6) and inferior leads (II, III, aVF) - due to asymmetric septal hypertrophy creating abnormal initial septal forces
  • Giant T-wave inversions in precordial leads (especially apical HCM variant - "apical HCM" or Yamaguchi syndrome, with massive negative T waves in V3-V5)
  • ST depression in lateral leads
  • Left atrial enlargement (broad, bifid P wave)
  • Left axis deviation
  • The ECG is abnormal in >90% of HCM patients

Quick Reference Summary

DiseaseKey ECG Finding
STEMIST elevation ≥1 mm in ≥2 contiguous leads + Q waves
NSTEMI/UAST depression, T inversion, no Q waves
Atrial FibrillationAbsent P waves, irregularly irregular RR
1st-degree AV blockPR > 200 ms, all P waves conduct
2nd-degree AV block (Wenckebach)Progressive PR lengthening, dropped beat
3rd-degree AV blockComplete AV dissociation, slow escape rhythm
LBBBQRS ≥120 ms, broad R in V5-V6, discordant ST-T
LVHHigh voltage (SV1+RV5 >35 mm), lateral strain pattern
Pulmonary EmbolismS1Q3T3, sinus tachycardia, right heart strain
HCMLVH + deep septal Q waves, giant T inversions
Sources:
  • Harrison's Principles of Internal Medicine 22E (2025), Chapters 247, 285, 286
  • Guyton & Hall Textbook of Medical Physiology, Chapter 13
  • Ganong's Review of Medical Physiology, 26th Edition, Chapter 29
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