Ecg diagnosis common disease
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ECG diagnosis common diseases electrocardiogram patterns 2025
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ECG patterns common diseases diagnosis electrocardiogram
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STEMI myocardial infarction ECG ST elevation
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atrial fibrillation ECG irregular rhythm no P waves
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complete heart block third degree AV block ECG
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ventricular tachycardia ECG wide complex tachycardia
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pericarditis ECG diffuse ST elevation saddle shape
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hyperkalemia ECG peaked T waves wide QRS sine wave
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ECG Diagnosis of Common Diseases
A 12-lead ECG records the heart's electrical activity across 10 electrodes. Systematic interpretation covers: rate → rhythm → axis → intervals (PR, QRS, QT) → P waves → ST segments / T waves → pathological Q waves.
1. Acute Myocardial Infarction (STEMI)
Key ECG features:
- ST elevation ≥1 mm in ≥2 contiguous limb leads, or ≥2 mm in ≥2 contiguous precordial leads
- Hyperacute T waves (tall, peaked) in the earliest phase
- Pathological Q waves (>40 ms wide, >25% of R wave amplitude) indicating transmural necrosis
- Reciprocal ST depression in leads facing away from the infarct zone
- New LBBB may be equivalent to STEMI in the right clinical context
Localisation by lead territory:
| Territory | Leads with STE | Artery |
|---|---|---|
| Anterior | V1–V4 | LAD |
| Anterolateral | V1–V6, I, aVL | Proximal LAD |
| Inferior | II, III, aVF | RCA (or LCx) |
| Lateral | I, aVL, V5–V6 | LCx |
| Posterior | Tall R + ST depression V1–V3 | RCA/LCx |
Tombstone ST elevation (massive convex STE) signals proximal LAD/left main occlusion — immediate reperfusion required.
2. NSTEMI / Unstable Angina
Key ECG features:
- ST depression ≥0.5 mm (horizontal or downsloping) — most specific for subendocardial ischemia
- T-wave inversions — symmetric, deep inversions particularly ominous (Wellens' pattern in V2–V3 = LAD stenosis)
- Normal ECG does NOT exclude NSTEMI (1–6% of ED chest pain patients with normal ECG have NSTEMI)
- Dynamic ECG changes (resolution/worsening with symptoms) confirm ACS
3. Atrial Fibrillation (AF)
Key ECG features:
- Irregularly irregular ventricular rhythm — no two R-R intervals are equal
- Absent P waves — replaced by fine fibrillatory (f) waves, best seen in V1 and lead II
- Narrow QRS (unless aberrant conduction/RBBB/WPW)
- Ventricular rate typically 110–160 bpm in uncontrolled AF
4. Atrial Flutter
Key ECG features:
- Sawtooth flutter waves at ~300 bpm (F waves), best seen in II, III, aVF, V1
- Regular or regularly irregular ventricular rate — most commonly 2:1 block (ventricular rate ~150 bpm)
- Narrow QRS (unless aberrancy)
- Important: a regular tachycardia at exactly 150 bpm should always raise suspicion for flutter with 2:1 block
5. Ventricular Tachycardia (VT)
Key ECG features:
- Wide complex tachycardia (QRS >120 ms) at rate >100 bpm
- AV dissociation — independent P waves and QRS complexes (pathognomonic when present)
- Capture beats (narrow complex among wide complexes) and fusion beats
- Positive/negative concordance across all precordial leads
- Rate typically 140–200 bpm; monomorphic (structural disease) vs polymorphic
Brugada criteria favor VT: absence of RS in precordial leads; RS interval >100 ms; AV dissociation; specific morphology criteria.
6. Ventricular Fibrillation (VF)
Key ECG features:
- Chaotic, irregular waveforms with no recognizable QRS complexes or P waves
- Coarse VF (large amplitude) vs fine VF (small amplitude, harder to distinguish from asystole)
- Immediately life-threatening — requires immediate defibrillation
7. Complete (Third-Degree) AV Block
Key ECG features:
- Complete AV dissociation — P waves and QRS bear no relationship
- P rate > QRS rate (e.g., P at 80 bpm, QRS escape at 30–50 bpm)
- Escape rhythm: junctional escape = narrow QRS (40–60 bpm); ventricular escape = wide QRS (20–40 bpm)
- Wide QRS escape = infra-Hisian block = more serious, pacemaker urgently required
8. First- and Second-Degree AV Block
| Type | PR Interval | QRS after each P | Notes |
|---|---|---|---|
| First-degree | >200 ms (>5 small squares) | Yes, always | Benign; often vagal/digoxin |
| Mobitz I (Wenckebach) | Progressive lengthening | Dropped beat after longest PR | Usually nodal; benign |
| Mobitz II | Fixed, normal or prolonged | Suddenly dropped (no warning) | Infra-nodal; risk of CHB; pacemaker often needed |
| 2:1 block | — | Every other P blocked | Can be Mobitz I or II; check context |
9. Bundle Branch Blocks
Left Bundle Branch Block (LBBB)
- QRS ≥120 ms
- Broad monophasic R in I, aVL, V5–V6
- Deep S (or QS) in V1
- No septal Q in lateral leads
- ST/T changes secondary to conduction delay
Right Bundle Branch Block (RBBB)
- QRS ≥120 ms
- rSR' (rabbit ears) in V1–V2
- Wide slurred S in I, V6
- ST depression and T-wave inversion in V1–V3 (secondary changes)
10. Pericarditis
Key ECG features (4 classic stages):
- Diffuse concave ("saddle-shaped") ST elevation in almost all leads EXCEPT aVR and V1 (which show ST depression)
- PR segment depression (most visible in lead II) — highly specific; aVR shows PR elevation
- ST returns to baseline, T waves flatten
- T-wave inversions (weeks later)
- Spodick's sign: downsloping TP segment
Differentiating from STEMI: pericarditis has diffuse distribution (not one coronary territory), concave (not convex) STE, and PR depression.
11. Hyperkalemia
Progressive ECG changes with rising K⁺:
| K⁺ Level | ECG Change |
|---|---|
| 5.5–6.5 | Tall peaked ("tented") T waves, narrow base |
| 6.5–7.5 | Prolonged PR, flattened/absent P waves |
| 7.5–8.0 | Widened QRS, left axis deviation |
| >8.0 | Sine-wave pattern, VF, asystole |
12. Pulmonary Embolism (PE)
Key ECG features (none are specific):
- Sinus tachycardia — most common finding
- S1Q3T3 pattern: deep S in I, Q wave and T-wave inversion in III
- Right axis deviation, new RBBB
- T-wave inversions in V1–V4 (right heart strain pattern)
- Sinus tachycardia + right heart strain in clinical context = presumptive PE until proven otherwise
13. WPW (Wolff–Parkinson–White) Syndrome
Key ECG features:
- Short PR interval (<120 ms)
- Delta wave — slurred upstroke of QRS
- Wide QRS (>120 ms)
- Secondary ST/T changes
- Risk of AF conducting rapidly via accessory pathway → can precipitate VF
14. Long QT Syndrome
Key ECG features:
- QTc >440 ms (men) or >460 ms (women) (Bazett's formula: QT ÷ √RR)
- Morphological T-wave changes (notched T, biphasic T)
- Risk of torsades de pointes (TdP) — a polymorphic VT that can degenerate to VF
- Causes: congenital channelopathies, drugs (antiarrhythmics, antibiotics, antipsychotics), hypokalemia, hypomagnesemia
15. Brugada Syndrome
Key ECG features:
- Type 1 (diagnostic): Coved-type ST elevation ≥2 mm with descending ST → negative T wave, in V1–V2 (or high precordial placement)
- Type 2: Saddleback morphology — not diagnostic without provocative test (ajmaline/flecainide)
- Risk of polymorphic VT/VF and sudden cardiac death, typically in young males at night/rest
- ICD is definitive treatment for symptomatic patients
Quick Reference Summary
| Condition | Most Characteristic Feature |
|---|---|
| STEMI | Convex STE in contiguous leads + reciprocal changes |
| AF | Irregularly irregular, absent P waves |
| VT | Wide complex tachycardia + AV dissociation |
| CHB | Independent P & QRS, bradycardia |
| Pericarditis | Diffuse concave STE + PR depression |
| LBBB | Wide QRS, monophasic R in V5–V6 |
| RBBB | Wide QRS, rSR' in V1, slurred S in V6 |
| Hyperkalemia | Peaked T waves → sine wave |
| PE | Sinus tach + S1Q3T3 + right heart strain |
| WPW | Short PR + delta wave |
| Long QT | QTc >440–460 ms |
| Brugada | Coved STE V1–V2, no ischemia |
Sources: Tintinalli's Emergency Medicine (9e), Braunwald's Heart Disease (15e), Rosen's Emergency Medicine — via the medical textbook library.
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