Please explain me ecg with changes and name of disease
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ECG (Electrocardiogram): Waves, Intervals, and Disease Patterns
The ECG records the heart's electrical activity across 12 leads. Each lead "looks" at the heart from a different angle, so one disease can produce changes in specific lead groups (called territories). Below is a complete, disease-by-disease breakdown.
Normal ECG Anatomy
| Component | Normal Value | What It Represents |
|---|---|---|
| P wave | <120 ms, <2.5 mm tall | Atrial depolarization (SA node fires) |
| PR interval | 120-200 ms | AV node conduction delay |
| QRS complex | <120 ms | Ventricular depolarization |
| ST segment | Isoelectric (flat) | Early ventricular repolarization |
| T wave | Upright in I, II, V3-V6 | Ventricular repolarization |
| QT interval | <440 ms (men), <460 ms (women) | Total ventricular electrical activity |
ECG Changes by Disease
1. ST-Elevation Myocardial Infarction (STEMI)
The most time-critical ECG diagnosis.
Stages of ECG evolution:
| Time | ECG Finding |
|---|---|
| Minutes (earliest) | Hyperacute T waves - tall, broad, peaked, asymmetrical. ST segment just beginning to rise at J point |
| Hours | ST elevation - convex ("domed" or "tombstone" shape), >1 mm in 2+ contiguous limb leads; >1.5 mm in women, >2 mm in men over 40 in V2-V3 |
| Hours-days | Pathological Q waves - >40 ms wide, >25% QRS height = irreversible myocardial death |
| Days-weeks | T wave inversion - deep, symmetrical in affected leads |
| Chronic | Persistent Q waves - marker of old infarction |
Territory-based STEMI localization:
| Territory | Leads with ST elevation | Culprit Artery |
|---|---|---|
| Anterior | V1-V4 | Left anterior descending (LAD) |
| Lateral (high) | I, aVL | Left circumflex or 1st diagonal |
| Lateral (low) | V5, V6 | Left circumflex |
| Inferior | II, III, aVF | Right coronary (90%) or left circumflex |
| Posterior | Tall R in V1-V2, horizontal ST depression V1-V3 | Right coronary or circumflex |
| Right ventricle | V1 + right-sided leads V3R-V6R | Right coronary |
| Left main / multivessel | ST elevation aVR + diffuse ST depression | Left main coronary |
De Winter pattern (STEMI-equivalent): J-point depression + prominent upsloping T waves in precordial leads + ST elevation in aVR. Indicates proximal LAD occlusion.
Wellens syndrome: Deep T-wave inversions or biphasic T waves in V2-V3 in a pain-free patient. Indicates critical proximal LAD stenosis about to cause anterior STEMI.
2. NSTEMI / Unstable Angina
- Horizontal or downsloping ST depression (>0.5 mm) in 2+ contiguous leads
- T wave inversion (symmetrical, deep)
- ST elevation in posterior leads (V8-V9) may indicate true posterior MI
- ECG may be normal - does NOT rule out NSTEMI
3. Atrial Fibrillation (AF)
- No visible P waves (replaced by irregular fibrillatory baseline "f" waves)
- Irregularly irregular RR intervals
- Normal narrow QRS (unless aberrant conduction)
4. Atrial Flutter
- Sawtooth flutter waves at ~300 bpm (negative in II, III, aVF)
- Regular RR intervals with 2:1, 3:1, or 4:1 block (ventricular rate ~150, 100, or 75 bpm)
- No true P waves
5. Heart Blocks
| Type | ECG Finding | Disease |
|---|---|---|
| 1st degree | PR interval >200 ms, every P conducts | Vagal tone, inferior MI, digoxin |
| 2nd degree Mobitz I (Wenckebach) | PR progressively lengthens then a QRS drops | Inferior MI, AV nodal disease |
| 2nd degree Mobitz II | Fixed PR, random dropped QRS (no warning) | Bundle of His disease, anterior MI |
| 3rd degree (complete) | P waves and QRS completely dissociated, escape rhythm | Inferior MI, Lyme disease, digoxin toxicity |
6. Bundle Branch Blocks
Left Bundle Branch Block (LBBB)
- QRS >120 ms
- Broad notched R in I, V5, V6 ("M" pattern)
- Deep S in V1 ("W" pattern)
- ST elevation in V1-V2 (discordant)
- New LBBB with chest pain = STEMI-equivalent until proven otherwise
Right Bundle Branch Block (RBBB)
- QRS >120 ms
- rSR' ("rabbit ears") in V1
- Wide S wave in I, V5, V6
- Seen in: PE, anterior MI, cor pulmonale, normal variant
7. Acute Pericarditis
- Diffuse saddle-shaped ST elevation in nearly all leads (except aVR and V1, which show ST depression)
- PR depression in II, V4-V6 (pathognomonic - due to atrial inflammation)
- PR elevation in aVR
- No reciprocal ST depression (unlike STEMI)
- No Q waves
8. Pulmonary Embolism (PE)
- Often non-specific changes
- Classic (but insensitive) S1Q3T3 pattern: deep S in I, Q wave in III, T inversion in III
- Sinus tachycardia (most common ECG finding)
- New RBBB or incomplete RBBB
- Right axis deviation
- T wave inversions in V1-V4 (right heart strain)
- Atrial fibrillation
9. Left Ventricular Hypertrophy (LVH)
- Tall R in lateral leads (I, aVL, V5, V6) + deep S in V1-V2
- Sokolow-Lyon criteria: S in V1 + R in V5 or V6 >35 mm
- ST depression + T wave inversion in lateral leads ("LVH with strain")
- May mimic STEMI (pseudo-infarction pattern)
10. Hyperkalemia
| K+ Level | ECG Change |
|---|---|
| Mild (~5.5-6.5 mEq/L) | Tall, peaked, narrow ("tented") T waves |
| Moderate (~6.5-7.5) | Widening of QRS, PR prolongation, flat P waves |
| Severe (>7.5) | Sine wave pattern - QRS merges with T wave |
| Critical | Ventricular fibrillation, asystole |
11. Hypokalemia
- Prominent U waves (after T wave, especially in V2-V3)
- Flat or inverted T waves
- ST depression
- QT prolongation (actually QU prolongation)
12. Long QT Syndrome
- QTc >440 ms (men), >460 ms (women)
- Risk of Torsades de Pointes (polymorphic VT)
- Causes: congenital (LQT1, LQT2, LQT3 syndromes), drugs (antiarrhythmics, antipsychotics, macrolides), hypokalemia, hypomagnesemia
13. Brugada Syndrome
- Right bundle branch block morphology + ST elevation in V1-V3 (Type 1: "coved" shape)
- ST elevation >2 mm with downward slope to inverted T wave
- Risk of sudden cardiac death from VF
- Sodium channelopathy (SCN5A mutation)
14. Wolff-Parkinson-White (WPW) Syndrome
- Short PR interval (<120 ms)
- Delta wave - slurred upstroke of QRS complex
- Wide QRS complex
- Pseudo-ST and T changes (secondary to abnormal depolarization)
- Risk of AF conducting rapidly down accessory pathway = life-threatening
15. Vasospastic (Prinzmetal's) Angina
- Transient ST elevation during episodes of spasm (spontaneous or provoked)
- ST elevation resolves completely with nitroglycerin or after spasm terminates
- Can trigger malignant arrhythmias
- Typically nocturnal or early morning
16. Digoxin Effect
- "Reverse tick" or "scooped" ST depression in lateral leads
- Shortened QT
- Prominent U waves
- (Note: digoxin toxicity causes AV blocks, bradycardia, PVCs in bigeminy)
17. Atrial Enlargement
| Type | ECG Finding |
|---|---|
| Left atrial enlargement | Broad notched P wave ("P mitrale") >120 ms, biphasic P in V1 |
| Right atrial enlargement | Tall peaked P wave ("P pulmonale") >2.5 mm in II, III, aVF |
18. Ventricular Tachycardia (VT)
- Wide QRS tachycardia (QRS >120 ms) at rate >100 bpm
- AV dissociation (P waves march independently)
- Fusion beats and capture beats (pathognomonic of VT)
- Concordance in precordial leads (all positive or all negative V1-V6)
Quick Reference Summary Table
| ECG Finding | Think Of |
|---|---|
| ST elevation (convex, territorial) | STEMI |
| Diffuse ST elevation (concave) + PR depression | Acute pericarditis |
| ST depression + T inversion | NSTEMI, ischemia, LVH strain |
| No P waves + irregular rhythm | Atrial fibrillation |
| Sawtooth P waves ~300/min | Atrial flutter |
| Progressive PR lengthening + dropped beat | Mobitz I (Wenckebach) |
| Fixed PR + randomly dropped QRS | Mobitz II |
| P-QRS dissociation | Complete (3rd degree) heart block |
| Tall peaked T waves | Hyperkalemia |
| Prominent U waves | Hypokalemia |
| Short PR + delta wave | WPW |
| Prolonged QTc | Long QT syndrome, drugs |
| RSR' in V1 + wide S in V1 | RBBB |
| Broad M-shaped R in I/V6 | LBBB |
| Coved ST elevation V1-V3 | Brugada syndrome |
| S1Q3T3 + sinus tach | Pulmonary embolism |
Sources:
- Rosen's Emergency Medicine: Concepts and Clinical Practice, Chapter 64 (Electrocardiographic Abnormalities in ACS, ST Segment Elevation, Differential Diagnosis)
- Fuster and Hurst's The Heart, 15th Edition (Vasospastic Angina, PE Electrocardiography)
- Guyton and Hall Textbook of Medical Physiology (Atrial Fibrillation ECG)
- Textbook of Family Medicine 9e (Arrhythmias - Long QT, Brugada)
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