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Explain most common heart diseases with ecg findings

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ECG findings myocardial infarction ST elevation

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atrial fibrillation ECG irregularly irregular rhythm absent P waves

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hypertrophic cardiomyopathy ECG left ventricular hypertrophy deep S waves

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pericarditis ECG diffuse ST elevation PR depression saddle shaped

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pulmonary embolism ECG S1Q3T3 right heart strain pattern

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complete heart block third degree AV block ECG dissociation

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Common Heart Diseases and Their ECG Findings

1. ST-Elevation Myocardial Infarction (STEMI)

Pathophysiology: Complete occlusion of a coronary artery → transmural ischemia/infarction.

ECG Findings:

FindingDetail
ST elevation>1 mm in ≥2 contiguous leads
Q wavesPathological Q waves (>0.04 s duration) — develop within hours
T-wave changesHyperacute peaked T-waves early; T-wave inversion in evolution
New LBBBEquivalent to STEMI — treat as occlusion
Reciprocal depressionST depression in leads opposite to injury zone (marks larger territory, higher mortality)

Localization by lead group (Tintinalli's Emergency Medicine):

TerritoryLeads with ST elevationCulprit artery
AnteriorV1–V4LAD
InferiorII, III, aVFRCA (ST III > II) or LCx (ST III < II)
LateralI, aVL, V5–V6LCx
PosteriorST depression V1–V3 (mirror image) → posterior leads V8–V9RCA/LCx
RV infarctionST elevation in V4RProximal RCA
"Elevation of aVR > V1 suggests left anterior descending artery occlusion." — Tintinalli's Emergency Medicine
Anterior STEMI (LAD occlusion):
Anterior STEMI ECG with ST elevation V1-V6
Inferior STEMI (RCA occlusion) with reciprocal changes:
Inferior STEMI ECG with ST elevation II III aVF and reciprocal depression I aVL

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

Pathophysiology: Partial occlusion / subendocardial ischemia — no full-thickness injury.

ECG Findings:

ConditionECG
NSTEMIST depression ≥1 mm in concordant leads; T-wave inversion
Unstable AnginaMost often normal or nonspecific; may have T-wave inversion
"Subendocardial infarction: T wave inversion or ST segment depression in concordant leads." — Rosen's Emergency Medicine

3. Atrial Fibrillation (AF)

Pathophysiology: Chaotic atrial electrical activity at 350–600 impulses/min; AV node conducts irregularly.

ECG Findings:

  • Absent P waves — replaced by irregular fibrillatory baseline (f-waves), best seen in V1
  • Irregularly irregular R-R intervals (no pattern to QRS timing)
  • Narrow QRS (unless aberrant conduction or pre-excitation)
  • Ventricular rate variable: slow (if treated/AV block) to rapid (>100 bpm = AF with RVR)
Atrial fibrillation with rapid ventricular response: absent P waves, irregularly irregular rhythm

4. Hypertrophic Cardiomyopathy (HCM)

Pathophysiology: Asymmetric septal hypertrophy → LV outflow obstruction, diastolic dysfunction, arrhythmia risk.

ECG Findings (Tintinalli's Emergency Medicine):

  • LV hypertrophy — deep S waves (V2–V3 ≥ 28 mm), tall R waves lateral leads
  • Left atrial enlargement — broad notched P wave in lead II, biphasic P in V1
  • Septal Q waves — narrow, deep Q waves in I, aVL, V4–V6 (≥0.3 mV) — pseudoinfarction pattern
  • T waves upright in leads with septal Q waves (distinguishes from ischemic Q waves where T waves are inverted)
  • Giant T-wave inversions in apical HCM (Yamaguchi syndrome) — deep symmetric inversions V3–V6
  • Arrhythmias: AF, atrial flutter, VT
HCM ECG: deep S waves (LVH), narrow septal Q waves in V5-V6 with upright T waves, atrial flutter 2:1
Apical HCM: giant T-wave inversions V3-V6

5. Pericarditis

Pathophysiology: Pericardial inflammation → diffuse epicardial irritation (subepicardial current of injury in all leads).

ECG Findings (4 classic stages):

StageFinding
Stage 1Diffuse concave ("saddle-shaped") ST elevation in all leads except aVR (ST depression) and V1; PR segment depression in most leads; PR elevation in aVR
Stage 2ST segments normalize; T waves flatten
Stage 3Diffuse T-wave inversion
Stage 4ECG returns to normal
Key distinguishing features from STEMI:
  • ST elevation is diffuse (all territories), not localized to one artery
  • Concave (saddle-shaped), not convex morphology
  • PR depression present
  • No reciprocal changes (except aVR)
  • No pathological Q waves
"Pericarditis: diffuse ST segment elevation; PR segment depression." — Rosen's Emergency Medicine
Spodick's sign: Downsloping TP segment (highly specific for pericarditis).
Acute pericarditis ECG: diffuse saddle-shaped ST elevation, PR depression, reciprocal changes in aVR

6. Heart Failure / Left Ventricular Hypertrophy

Pathophysiology: Chronic pressure/volume overload → LV remodeling, hypertrophy.

ECG Findings:

  • Sokolow-Lyon criteria for LVH: S in V1 + R in V5 or V6 > 35 mm
  • "Strain" pattern: ST depression and T-wave inversion in lateral leads (I, aVL, V5–V6)
  • Left axis deviation
  • Left atrial enlargement (bifid P wave in II, biphasic in V1)
  • Left bundle branch block (LBBB) — common in dilated cardiomyopathy/HF
  • Non-specific ST-T changes
"The resting ECG may reveal various conduction disturbances, most frequently left bundle branch block and left anterior fascicular block." — Goldman-Cecil Medicine

7. Pulmonary Embolism (PE)

Pathophysiology: Acute RV pressure overload from pulmonary artery obstruction → RV strain pattern.

ECG Findings (Tintinalli's Emergency Medicine, Fuster and Hurst's The Heart):

  • Sinus tachycardia — most common finding (HR >100)
  • S1Q3T3 pattern — S wave in lead I, Q wave in lead III, T-wave inversion in lead III (McGinn-White sign)
  • T-wave inversion V1–V4 — right precordial ischemia from RV strain
  • Incomplete or complete RBBB
  • Right axis deviation
  • "P pulmonale" — tall peaked P wave in lead II (≥2.5 mm) from right atrial enlargement
  • ECG may be entirely normal in ~30% of cases
"Findings of acute pulmonary hypertension on ECG include a heart rate >100 beats/min, T-wave inversion in leads V1 to V4, incomplete or complete right bundle branch block, and the S1-Q3-T3 pattern." — Tintinalli's Emergency Medicine
PE ECG: S1Q3T3 pattern, sinus tachycardia, right heart strain

8. Complete (Third-Degree) AV Block

Pathophysiology: Total failure of AV conduction → atria and ventricles beat independently.

ECG Findings:

  • P waves and QRS complexes completely dissociated — no relationship (P waves "march through" QRS/T waves)
  • Regular P-P intervals at normal/faster atrial rate
  • Regular R-R intervals at slow escape rate
  • Escape rhythm:
    • Junctional (AV nodal disease): narrow QRS, rate 40–60 bpm
    • Ventricular (infra-Hisian): wide QRS >120 ms, rate 20–40 bpm
Causes: inferior MI (usually transient), Lyme disease, infiltrative disease, post-surgical.
Complete heart block: P waves and wide QRS complexes completely dissociated

9. Wolff-Parkinson-White (WPW) Syndrome

Pathophysiology: Accessory pathway (Bundle of Kent) bypasses the AV node → ventricular pre-excitation.

ECG Findings:

  • Short PR interval (<120 ms) — early ventricular activation
  • Delta wave — slurred upstroke of QRS (pre-excitation)
  • Wide QRS — fusion beat (delta + normal conduction)
  • Discordant ST-T changes (secondary to abnormal depolarization)
  • Can have pseudo-Q waves and ST changes mimicking MI
  • Associated with orthodromic SVT (regular narrow complex tachycardia) and AF with rapid ventricular response (irregular, wide complex — dangerous)

10. Dilated Cardiomyopathy

Pathophysiology: Ventricular dilation + systolic dysfunction from various causes.

ECG Findings:

  • LBBB — very common (reflects impaired conduction through dilated ventricle)
  • LVH criteria — but voltage often low in the most dilated hearts
  • Poor R-wave progression across precordial leads
  • Non-specific ST-T changes
  • AF and ventricular ectopy are frequent

Quick Reference Summary

DiseaseKey ECG Pattern
STEMIST elevation (contiguous leads), Q waves, new LBBB
NSTEMIST depression, T-wave inversion
Atrial FibrillationAbsent P waves, irregularly irregular
HCMLVH, narrow septal Q waves, upright T waves; giant TWI in apical type
PericarditisDiffuse saddle-shaped ST ↑, PR depression, no reciprocal changes
Heart Failure/LVHLVH criteria, strain pattern, LBBB
Pulmonary EmbolismTachycardia, S1Q3T3, RBBB, TWI V1–V4
Complete Heart BlockAV dissociation, bradycardia, slow escape rhythm
WPWShort PR, delta wave, wide QRS
Dilated CardiomyopathyLBBB, poor R-wave progression, arrhythmias
Sources: Rosen's Emergency Medicine; Tintinalli's Emergency Medicine; Goldman-Cecil Medicine; Harrison's Principles of Internal Medicine 22E; Fuster and Hurst's The Heart, 15th Ed.
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