Tomorrow i have therapy exam. Tell me all the ECG and disease related to it.
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I now have comprehensive content from the textbooks. Let me compile a thorough, exam-ready ECG guide.
📋 ECG & Related Diseases — Complete Therapy Exam Guide
1. ECG BASICS — WAVES, INTERVALS, SEGMENTS
| Component | Normal Duration | What It Represents |
|---|---|---|
| P wave | <120 ms | Atrial depolarization |
| PR interval | 120–200 ms | AV conduction time |
| QRS complex | 60–100 ms | Ventricular depolarization |
| ST segment | Isoelectric | Early ventricular repolarization |
| T wave | Upright | Ventricular repolarization |
| QT interval | <440 ms (corrected) | Total ventricular activity |
| U wave | Small, upright | Purkinje repolarization (prominent in hypokalemia) |
2. MYOCARDIAL INFARCTION (MI)
Pathophysiology of ECG Changes
Three ionic events explain MI changes (Ganong's Review of Medical Physiology):
| Defect in Infarcted Cells | Current Flow | ECG Change in Overlying Leads |
|---|---|---|
| Rapid repolarization (K⁺ efflux) | Out of infarct | ST elevation |
| Decreased resting membrane potential (K⁺ loss) | Into infarct | TQ depression → ST elevation |
| Delayed depolarization | Out of infarct | ST elevation |
Temporal ECG Evolution of MI
| Time | ECG Change |
|---|---|
| Minutes–Hours | Hyperacute tall T waves → ST elevation (>1 mm in 2+ contiguous leads) |
| Hours–Days | Q waves appear; ST still elevated; T wave begins inverting |
| Days–Weeks | Deep symmetric T wave inversion; ST returns to baseline |
| Weeks–Months (late) | Persistent Q waves may remain; T wave may normalize |
"The hallmark of acute MI is elevation of the ST segments in the leads overlying the area of infarction." — Ganong's
STEMI vs NSTEMI vs Unstable Angina
| STEMI | NSTEMI | Unstable Angina | |
|---|---|---|---|
| ECG | ST elevation (>1 mm, ≥2 leads) | ST depression, deep T inversion | Usually normal or nonspecific |
| Troponin | Elevated | Elevated | Normal |
| Mechanism | Complete occlusion | Incomplete occlusion or collaterals | No necrosis |
MI Localization by Leads
| Territory | Culprit Artery | Leads with ST Elevation |
|---|---|---|
| Anterior | LAD | V1–V4 |
| Lateral | LCx | I, aVL, V5–V6 |
| Inferior | RCA (90%) | II, III, aVF |
| Posterior (inferobasal) | RCA/LCx | ST depression V1–V3 (reciprocal); ST elevation V7–V9 |
| Right ventricular | Proximal RCA | ST elevation V4R |
Key exam point: ST depression in V1–V4 may represent posterior MI — obtain posterior leads (V7–V9). (Rosen's Emergency Medicine)
New LBBB + Chest Pain
A new LBBB with suspected ischemia is treated equivalent to STEMI — use the Sgarbossa criteria to detect AMI in LBBB:
- ST elevation ≥1 mm concordant with QRS → most specific
- ST depression ≥1 mm in V1–V3 concordant with QRS
- ST elevation ≥5 mm discordant with QRS (modified: ST/S ratio >0.25)
3. ARRHYTHMIAS
Supraventricular Arrhythmias
Atrial Fibrillation (AF)
- ECG: Irregularly irregular R-R intervals; absent P waves; fibrillatory baseline (f waves, >350/min)
- Rate: Ventricular rate 100–180 bpm (uncontrolled)
- Risk: Stroke (use CHADS₂/CHA₂DS₂-VASc to assess)
- Causes: HTN, valvular disease, hyperthyroidism, alcohol, heart failure
Atrial Flutter
- ECG: Regular "sawtooth" flutter waves at ~300/min (F waves); typically 2:1 AV block → ventricular rate ~150 bpm
- Distinction from AF: Flutter is regular with discrete F waves; AF is irregular
Multifocal Atrial Tachycardia (MAT)
- ECG: ≥3 different P wave morphologies in a single lead; no consistent PP, PR, or RR intervals; irregularly irregular at 100–180 bpm
- Confused with: AF
- Cause: COPD (most common)
Paroxysmal Supraventricular Tachycardia (PSVT / AVNRT)
- ECG: Narrow complex, regular tachycardia; P waves hidden in or just after QRS; rate 150–250 bpm
- Mechanism: Reentry within AV node (AVNRT) or accessory pathway (AVRT)
4. AV CONDUCTION BLOCKS
| Degree | ECG Finding | Clinical Significance |
|---|---|---|
| 1st degree | PR > 200 ms; all P waves conduct | Benign; no treatment needed |
| 2nd degree Mobitz I (Wenckebach) | Progressive PR prolongation → dropped QRS; group beating | Usually AV node level; benign, may not progress |
| 2nd degree Mobitz II | Fixed PR; sudden non-conducted P wave; often with BBB | Below AV node; high risk of progression to complete block |
| 2:1 AV block | Every other P wave non-conducted | Difficult to classify; narrow QRS → Mobitz I likely; wide QRS → Mobitz II likely |
| 3rd degree (Complete heart block) | Complete AV dissociation; P rate > ventricular escape rate | Medical emergency; requires pacemaker |
"Type II block, particularly if bundle branch block is present, often antedates progression to complete heart block." — Washington Manual
5. BUNDLE BRANCH BLOCKS (BBB)
Right BBB (RBBB)
- QRS > 120 ms
- V1: rSR' (M-shaped / "rabbit ears")
- V6: Wide, slurred S wave
- Causes: Normal variant, pulmonary embolism (acute RBBB), congenital, degenerative, MI
Left BBB (LBBB)
- QRS > 120 ms
- V1: Broad rS or QS complex
- V5–V6: Broad, notched R wave (no septal Q waves)
- Clinical: New LBBB = rule out acute MI; causes ventricular dyssynchrony and can worsen heart failure
- Prevalence: Up to 25% of heart failure patients have LBBB
Fascicular Blocks (Hemiblocks)
| Block | Axis | ECG Features |
|---|---|---|
| Left anterior fascicular block (LAFB) | −45° to −90° (left axis deviation) | Small R in II, III, aVF; tall R in I, aVL |
| Left posterior fascicular block (LPFB) | +120° or more (right axis deviation) | Must exclude RVH, PE, lateral MI |
6. ELECTROLYTE DISTURBANCES & ECG
Hyperkalemia (DANGEROUS — potentially lethal)
| K⁺ Level | ECG Change |
|---|---|
| Mildly elevated | Tall, peaked (tented) T waves — first change |
| Moderately elevated | PR prolongation, widening QRS, atrial paralysis |
| Severely elevated | Sine wave pattern → ventricular fibrillation → asystole |
Hypokalemia
- Prolonged PR interval
- Prominent U waves (key finding)
- Late T wave inversion in precordial leads
- T and U waves may merge → apparent QTc prolongation
Hypercalcemia
- Shortened QT interval
Hypocalcemia
- Prolonged QT interval (T wave unchanged, ST lengthened)
7. WPW (WOLFF-PARKINSON-WHITE) SYNDROME
- Mechanism: Accessory pathway (Bundle of Kent) bypasses AV node → ventricular pre-excitation
- ECG Triad:
- Short PR interval (<120 ms)
- Delta wave (slurred upstroke of QRS)
- Wide QRS
- Risk: AF with rapid conduction through accessory pathway → ventricular fibrillation
- Treatment: Avoid AV nodal blockers (digoxin, verapamil, adenosine) in AF + WPW
8. PERICARDITIS
- ECG (4 stages):
| Stage | ECG |
|---|---|
| Stage I (acute) | Diffuse ST elevation (concave/saddle-shaped) in most leads; PR depression |
| Stage II | ST normalizes; PR depression persists |
| Stage III | T wave inversion |
| Stage IV | ECG normalizes |
- Key distinguishing feature from MI: ST elevation is diffuse (not localized to a territory); PR depression present; no reciprocal ST depression (except aVR)
9. PULMONARY EMBOLISM (PE)
- Most common ECG: Sinus tachycardia (nonspecific but most frequent)
- Classic (but uncommon): S1Q3T3 — S wave in lead I, Q wave + T wave inversion in lead III
- New RBBB (right heart strain)
- Right axis deviation
- ST changes suggesting RV strain
10. OTHER DISEASE-SPECIFIC ECG PATTERNS
| Condition | Key ECG Finding |
|---|---|
| Left ventricular hypertrophy (LVH) | Sokolow-Lyon: S in V1 + R in V5/V6 ≥35 mm; strain pattern (ST depression + T inversion in lateral leads) |
| Right ventricular hypertrophy (RVH) | Right axis deviation; tall R in V1; deep S in V5–V6 |
| Long QT syndrome | QTc >440 ms (male) / >460 ms (female); risk of torsades de pointes |
| Brugada syndrome | Pseudo-RBBB + ST elevation in V1–V3 (coved/saddleback pattern); risk of sudden death |
| Hyperkalemia | Peaked T waves → sine wave |
| Hypothermia | Osborn (J) waves at the QRS-ST junction; bradycardia |
| Digitalis toxicity | "Reverse tick" / scooped ST depression; prolonged PR; various arrhythmias |
| Pneumothorax (left-sided) | Mimics anterior MI — rightward axis shift, decreased precordial R-wave voltage |
| Takotsubo cardiomyopathy | ST elevation or deep T wave inversions without obstructive CAD; associated with emotional stress |
| Acute myocarditis | Similar to MI (ST elevation + troponin rise); requires coronary imaging to differentiate |
11. QUICK EXAM MEMORY TRICKS
| Finding | Diagnosis |
|---|---|
| Irregularly irregular, no P waves | AF |
| Sawtooth at 300/min | Atrial Flutter |
| Short PR + delta wave + wide QRS | WPW |
| Diffuse ST elevation + PR depression | Pericarditis |
| Peaked T → wide QRS → sine wave | Hyperkalemia |
| Prominent U waves | Hypokalemia |
| S1Q3T3 + new RBBB | PE |
| Osborn J waves | Hypothermia |
| New LBBB + chest pain | Treat as STEMI (Sgarbossa criteria) |
| rSR' in V1, wide S in V6 | RBBB |
| Broad notched R in V5–V6 | LBBB |
Sources: Ganong's Review of Medical Physiology 26th Ed. | Rosen's Emergency Medicine | Goldman-Cecil Medicine | Washington Manual of Medical Therapeutics | Tintinalli's Emergency Medicine
Good luck on your exam tomorrow! This covers the core ECG-disease relationships you're most likely to be tested on in a therapy/internal medicine context.
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