259.1 🎓 醫孞生版

259.1.0.1 📌 䞀頁重點

259.1.0.1.1 Systematic ECG Approach
  1. Standardization + paper speed (25 mm/sec standard) + calibration (10 mm/mV)
  2. Rate (300 / number of large boxes, or count R-R)
  3. Rhythm (regular vs irregular; sinus vs other)
  4. Axis (normal -30 to +90°; deviation calculations)
  5. Intervals (PR, QRS, QT)
  6. Waves (P, QRS, T, U morphology)
  7. Chambers (atrial + ventricular enlargement)
  8. Ischemia + injury + infarction (ST changes, T inversion, Q waves)
  9. Other (Wolff-Parkinson-White, channelopathy, electrolyte, drug effects, devices)
259.1.0.1.2 Normal Values
  • Rate: 60-100 bpm (sinus)
  • PR: 120-200 ms (3-5 small boxes)
  • QRS: 60-100 ms (< 3 small boxes for normal)
  • QT corrected (QTc): < 440 ms men / < 460 ms women
  • Axis: -30° to +90° (normal)
259.1.0.1.3 Common Findings + Significance
259.1.0.1.3.1 Bradycardia
  • Sinus bradycardia (< 60 bpm): athletes, sleep, drugs (BB, CCB, digoxin), hypothyroid, ↑ ICP, MI
  • AV blocks: 1° (PR > 200 ms; usually benign), 2° Mobitz I/II, 3° complete
  • Junctional rhythm: AV node escape (HR 40-60); no P wave or inverted P
  • Idioventricular rhythm: ventricular escape (HR 20-40)
259.1.0.1.3.2 Tachycardia (HR > 100)
  • Sinus tachycardia: fever, hypovolemia, anemia, hyperthyroidism, drugs, pain, PE
  • Atrial fibrillation (AF): irregularly irregular, no P waves, varying R-R
  • Atrial flutter: saw-tooth pattern (typical: 300 atrial rate, often 2:1 conduction = 150 ventricular)
  • AVNRT: regular narrow complex, retrograde P (often hidden in QRS or follows in inferior leads)
  • AVRT (e.g., WPW): orthodromic narrow QRS; antidromic wide
  • Ventricular tachycardia (VT): wide complex, AV dissociation, capture/fusion beats
  • Ventricular fibrillation (VF): chaotic, no organized complexes
259.1.0.1.3.3 Ischemia / Injury / Infarction
  • ST elevation (STEMI): ≥ 1 mm in 2 contiguous leads (≥ 2 mm in V2-V3 men; ≥ 1.5 mm V2-V3 women)
  • ST depression: ischemia (NSTEMI), digitalis effect
  • T-wave inversion: ischemia, drug effect, hypokalemia
  • Q waves: prior MI (chronic; > 1 mm wide or > 25% R height)
  • Hyperacute T-waves: very early MI (peaked)
259.1.0.1.4 Localization of MI (Lead Distribution)
  • Anterior (LAD): V1-V4
  • Septal: V1-V2
  • Lateral: V5-V6, I, aVL
  • Inferior (RCA usually; LCx 20%): II, III, aVF
  • Posterior: V1-V2 reciprocal ST depression (mirror image)
  • Right ventricular: V4R (right-sided V4)
  • Anterolateral: V1-V6, I, aVL
259.1.0.1.5 Hypertrophy
259.1.0.1.5.1 Left Ventricular Hypertrophy (LVH)
  • Sokolow-Lyon: S in V1 + R in V5/V6 ≥ 35 mm
  • Cornell: R in aVL + S in V3 > 28 mm men, > 20 mm women
  • Strain pattern: ST depression + T inversion in V5-V6, I, aVL
  • Causes: HTN, AS, HCM, severe AR, MR
259.1.0.1.5.2 Right Ventricular Hypertrophy (RVH)
  • R/S ratio > 1 in V1
  • R in V1 > 7 mm
  • Right axis deviation
  • T-wave inversion V1-V3
  • Causes: pulmonary HTN, pulmonic stenosis, TR
259.1.0.1.5.3 Left Atrial Enlargement
  • P wave > 120 ms
  • Bifid P in II, III, aVF
  • Biphasic P in V1 with terminal negative deflection > 1 mm × 1 mm
259.1.0.1.5.4 Right Atrial Enlargement
  • P wave > 2.5 mm in II, III, aVF
  • Peaked P (“P pulmonale”)
  • Causes: PHTN, severe TR, TS, COPD
259.1.0.1.6 Conduction Abnormalities
259.1.0.1.6.1 Bundle Branch Blocks
  • RBBB: QRS > 120 ms; rSR’ or M-shape in V1; slurred S in V6
  • LBBB: QRS > 120 ms; broad notched R in V6; QS or rS in V1
  • LAFB: left axis deviation < -45°; qR in I, aVL
  • LPFB: right axis deviation > 90°; rule out RVH, lateral MI
259.1.0.1.6.2 AV Blocks
  • 1°: PR > 200 ms (uniform delay)
  • 2° Mobitz I (Wenckebach): progressive PR prolongation → dropped beat
  • 2° Mobitz II: constant PR + dropped beats
  • 3° (Complete): AV dissociation; atrial + ventricular independent rates
259.1.0.1.7 WPW Syndrome
  • Pre-excitation pattern:
    • Short PR (< 120 ms)
    • Delta wave (slurred upstroke of QRS)
    • Wide QRS (> 110 ms)
  • Risk of supraventricular tachycardia + AF with rapid conduction (potential VF)
259.1.0.1.8 Electrolyte + Drug Effects
259.1.0.1.8.1 Hyperkalemia
  • Peaked T-waves (early)
  • Flattened P, prolonged PR, widened QRS → sine wave pattern in severe
259.1.0.1.8.2 Hypokalemia
  • U-waves (after T)
  • Flattened T
  • ST depression
259.1.0.1.8.3 Hypercalcemia
  • Short QT
259.1.0.1.8.4 Hypocalcemia
  • Long QT (without T-wave abnormality)
259.1.0.1.8.5 Digoxin Effect
  • “Scooped” ST depression
  • T-wave inversion
  • Not toxic (just chronic use)
259.1.0.1.8.6 Digoxin Toxicity
  • PVCs, AV block, atrial tachycardia with block, sinus bradycardia, ventricular arrhythmia
  • Often associated with hypokalemia / hypomagnesemia
259.1.0.1.9 Channelopathies + Arrhythmogenic
259.1.0.1.9.1 Long QT Syndrome
  • QTc > 460 women, > 440 men (variable cutoffs)
  • Risk of torsades de pointes
  • Congenital (Romano-Ward, Jervell-Lange-Nielsen) vs acquired (drugs, electrolyte)
259.1.0.1.9.2 Brugada Syndrome
  • ST elevation in V1-V3 (specific patterns)
  • Type 1: coved
  • Type 2: saddle-back (≥ 0.5 mV)
  • Risk of VF + sudden cardiac death
  • SCN5A mutations
259.1.0.1.9.3 Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
  • Epsilon wave (small upstroke in V1 after QRS)
  • T-wave inversion V1-V3
  • Risk of VT + SCD
259.1.0.1.9.4 Catecholaminergic Polymorphic VT (CPVT)
  • Exercise-induced bidirectional VT
  • RYR2 mutations
  • Risk of SCD
259.1.0.1.10 Pacemakers + Devices
  • Atrial paced: spike before P
  • Ventricular paced: spike before QRS (looks LBBB)
  • Dual chamber: spikes before P + QRS
  • LBBB / paced rhythm: harder to diagnose ischemia (Sgarbossa criteria)

259.1.0.2 1⃣ Systematic Approach Detailed

259.1.0.2.1 Step 1: Standardization
  • 25 mm/sec paper speed (standard); 10 mm/mV calibration
  • Check on left margin of ECG strip
  • Half standard (5 mm/mV) sometimes used for tall QRS
259.1.0.2.2 Step 2: Rate
  • Regular:
    • 300 / large boxes between R-R (300, 150, 100, 75, 60, 50)
    • Or count R-R seconds + invert
  • Irregular:
    • Count R’s in 10-second strip × 6
259.1.0.2.3 Step 3: Rhythm
  • Sinus: P before every QRS, consistent P morphology, regular intervals
  • Sinus arrhythmia: P waves normal, R-R irregular (often respiratory)
  • Non-sinus: atrial, junctional, ventricular
259.1.0.2.4 Step 4: Axis
  • Normal axis: -30° to +90°
  • Left axis deviation (-30° to -90°): LAFB, LBBB, LVH, inferior MI
  • Right axis deviation (+90° to +180°): RVH, LPFB, lateral MI, COPD
  • Extreme axis (-90° to ±180°): “northwest” axis; ventricular rhythm

Quick method: - I + aVF positive → normal axis - I positive, aVF negative → left axis deviation (check II — if positive, normal-left; if negative, LAD) - I negative, aVF positive → right axis deviation

259.1.0.2.5 Step 5: Intervals
259.1.0.2.5.1 PR Interval
  • 120-200 ms normal
  • < 120 ms: pre-excitation (WPW)

  • 200 ms: 1° AV block

259.1.0.2.5.2 QRS Duration
  • < 100 ms normal
  • 100-120 ms: incomplete BBB or non-specific

  • 120 ms: complete BBB or ventricular rhythm

259.1.0.2.5.3 QT / QTc
  • QT = end of QRS to end of T
  • QTc = QT / √(R-R interval in seconds)
  • Bazett formula: most common
  • Normal: men < 440 ms, women < 460 ms

  • 500 ms = high risk for torsades

259.1.0.2.6 Step 6: Waves
259.1.0.2.6.1 P-Wave Morphology
  • Sinus: upright in I + II
  • Inverted: ectopic atrial rhythm, junctional
  • Bifid (M-shaped in II): LAE
  • Peaked in II: RAE
259.1.0.2.6.2 QRS Morphology
  • Pathologic Q waves: > 1 mm wide or > 25% R height
  • RBBB pattern: rSR’ in V1
  • LBBB pattern: notched R in V6, QS in V1
  • Delta wave: WPW
259.1.0.2.6.3 T-Wave Abnormalities
  • Inverted: ischemia (recent or old), digoxin effect, hypokalemia, LVH strain
  • Peaked: hyperkalemia, hyperacute MI
  • Flattened: ischemia, hypokalemia
259.1.0.2.7 Step 7: Chambers (Hypertrophy + Enlargement)
259.1.0.2.7.1 LVH (Sokolow-Lyon)
  • S in V1 + R in V5 or V6 ≥ 35 mm
  • Plus strain (ST depression + T inversion lateral leads)
259.1.0.2.7.2 Right Atrial Enlargement (RAE)
  • P > 2.5 mm in II (P pulmonale)
259.1.0.2.7.3 Left Atrial Enlargement (LAE)
  • P > 120 ms or bifid in II (P mitrale)
  • Biphasic P in V1 with prominent negative deflection
259.1.0.2.8 Step 8: ST-T Changes (Ischemia / Injury / Infarction)
259.1.0.2.8.1 STEMI (ST Elevation MI)
  • ≥ 1 mm in ≥ 2 contiguous leads (any limb leads)
  • ≥ 2 mm in V2-V3 men; ≥ 1.5 mm V2-V3 women
  • Acute onset → emergency PCI / thrombolysis
259.1.0.2.8.2 NSTEMI / Unstable Angina
  • ST depression (horizontal or downsloping)
  • T-wave inversion
  • Hyperacute T-waves (early)
259.1.0.2.8.3 Q Waves
  • Old infarction marker
  • Width > 1 mm or > 25% R-wave height
  • Persistent (chronic)
259.1.0.2.8.4 Reciprocal Changes
  • ST depression in opposite leads (when ST elevation present)
  • Reinforces diagnosis of STEMI
259.1.0.2.8.5 LBBB + Suspected MI (Sgarbossa Criteria)
  • Concordant ST elevation ≥ 1 mm (same direction as QRS): 5 points
  • Concordant ST depression ≥ 1 mm in V1-V3: 3 points
  • Discordant ST elevation ≥ 5 mm: 2 points
  • ≥ 3 points = likely STEMI
  • Modified Sgarbossa criteria more sensitive

259.1.0.3 2⃣ MI Localization

Leads with STEMI Region Likely Artery
V1-V4 Anterior LAD
V1-V2 Septal LAD (proximal)
V5-V6, I, aVL Lateral LCx or LAD diagonal
II, III, aVF Inferior RCA (80%) or LCx (20%)
V4R Right Ventricle Proximal RCA
V1-V2 reciprocal ST↓ + tall R waves Posterior LCx or RCA
V1-V6, I, aVL Anterolateral LAD proximal
259.1.0.3.1 Inferior MI Workup
  • Always do V4R (right-sided lead V4) → RV infarction
  • Posterior leads (V7-V9) optional
  • RV infarction: hypotension with nitroglycerin → fluid resuscitation
259.1.0.3.2 Reciprocal Changes
  • Inferior MI: ST depression in I, aVL (reciprocal)
  • Anterior MI: ST depression in II, III, aVF (reciprocal — sometimes seen)

259.1.0.4 3⃣ Long QT + Torsades

259.1.0.4.1 Long QT Causes
259.1.0.4.1.1 Congenital
  • LQT1 (KCNQ1), LQT2 (KCNH2), LQT3 (SCN5A) — most common
  • Romano-Ward (autosomal dominant)
  • Jervell-Lange-Nielsen (autosomal recessive + deafness)
259.1.0.4.1.2 Acquired (Common Causes)
  • Drugs: antiarrhythmics (Ia, III), antibiotics (macrolides, FQ), antifungals (fluconazole, voriconazole), antipsychotics, antidepressants (TCAs, citalopram), antiemetics (ondansetron), methadone
  • Electrolyte: hypokalemia, hypomagnesemia, hypocalcemia
  • Bradycardia
  • Stroke / CNS event
  • Liver / renal failure
  • Hypothyroidism
  • MI / cardiac ischemia
259.1.0.4.2 Management Acquired Long QT
  • Stop offending drug
  • Correct electrolytes (K, Mg, Ca)
  • Treat underlying
  • Magnesium 2 g IV for torsades
  • Defibrillation for sustained VF / VT

259.1.0.5 4⃣ Common Arrhythmia ECG Patterns

259.1.0.5.1 Sinus Bradycardia
  • Rate < 60 bpm
  • Regular rhythm, normal P-QRS
259.1.0.5.2 AV Blocks
259.1.0.5.2.1 1° AV Block
  • PR > 200 ms
  • Every P followed by QRS
259.1.0.5.2.2 2° Mobitz Type I (Wenckebach)
  • Progressive PR prolongation → dropped QRS
  • Usually benign
259.1.0.5.2.3 2° Mobitz Type II
  • Constant PR + dropped beats
  • Often diseased His-Purkinje → may progress to complete block
  • Pacemaker often indicated
259.1.0.5.2.4 3° (Complete AV Block)
  • AV dissociation
  • Atrial rate > ventricular rate
  • Atria + ventricles independent
259.1.0.5.3 Bundle Branch Blocks
259.1.0.5.3.1 RBBB
  • QRS > 120 ms
  • rSR’ (M-shape) in V1
  • Slurred wide S in I, V6
  • Often without underlying disease in healthy
259.1.0.5.3.2 LBBB
  • QRS > 120 ms
  • Broad notched R in V6 + I
  • QS or rS in V1
  • Almost always underlying disease (HTN, ischemia, cardiomyopathy)
259.1.0.5.4 Fascicular Blocks
  • LAFB: Left axis deviation; qR in I, aVL; rS in II, III, aVF
  • LPFB: Right axis deviation; rS in I; qR in III; (after excluding RVH + lateral MI)
259.1.0.5.5 Atrial Fibrillation (AF)
  • Irregularly irregular rhythm
  • No discrete P waves (fibrillatory baseline)
  • Varying R-R intervals
  • Often rapid ventricular response (HR > 100)
259.1.0.5.6 Atrial Flutter
  • Saw-tooth pattern (especially II, III, aVF)
  • Atrial rate ~ 300 bpm
  • Often 2:1 AV conduction → ventricular rate 150 bpm
259.1.0.5.7 Supraventricular Tachycardia (SVT)
259.1.0.5.7.1 AVNRT
  • Narrow complex, regular, rate 150-220 bpm
  • Retrograde P often hidden in QRS or just after (pseudo-S in II, III, aVF; pseudo-R’ in V1)
259.1.0.5.7.2 AVRT (e.g., WPW)
  • Orthodromic: narrow complex (conducts down AV node + up accessory pathway)
  • Antidromic: wide complex (conducts down accessory pathway + up AV node)
259.1.0.5.8 Ventricular Tachycardia (VT)
  • Wide QRS (> 120 ms)
  • Rate 100-250 bpm
  • AV dissociation
  • Capture / fusion beats
  • Concordance (all QRS positive or negative across precordium)
259.1.0.5.9 Ventricular Fibrillation (VF)
  • Chaotic, no organized complexes
  • No P, no QRS, no T
  • Lethal — emergent defibrillation
259.1.0.5.10 Asystole
  • Flat line
  • No electrical activity
  • Confirm in multiple leads
259.1.0.5.11 Pulseless Electrical Activity (PEA)
  • ECG shows organized rhythm
  • No pulse
  • Underlying cause (Hs and Ts)

259.1.0.6 5⃣ Specific Patterns

259.1.0.6.1 Hyperkalemia (Progressive)
  1. Peaked T-waves (K > 5.5 mEq/L)
  2. Flattened P + prolonged PR (K > 6.5)
  3. Widened QRS (K > 7)
  4. Sine wave pattern (K > 8)
  5. Asystole / VF (K > 9)
259.1.0.6.2 Hypokalemia
  • U-wave (after T)
  • Flattened T
  • ST depression
  • Long QT
259.1.0.6.3 Pericarditis
  • Diffuse ST elevation (concave up, “smiley face”)
  • PR depression (reciprocal in aVR + V1)
  • ST in most leads except aVR + V1 (which show depression)
  • Eventual normalization + T inversion (Wellens-like)
259.1.0.6.4 Pulmonary Embolism
  • S1Q3T3 pattern (S in I, Q in III, inverted T in III)
  • Sinus tachycardia
  • Right bundle branch block
  • Right axis deviation
  • T-wave inversion V1-V3
259.1.0.6.5 Pneumothorax (Left-Sided)
  • Decreased R-wave amplitude
  • Right axis deviation
  • ST changes (variable)
259.1.0.6.6 Brugada Syndrome
  • ST elevation V1-V3
  • Type 1: coved (downsloping)
  • Type 2: saddle-back
  • Risk of VF, SCD
259.1.0.6.7 WPW Syndrome
  • Pre-excitation: short PR + delta wave + wide QRS
  • Risk of SVT (orthodromic AVRT)
  • AF with WPW: rapid conduction down accessory pathway → can degenerate to VF
  • Avoid AV nodal blockers (BB, CCB, digoxin) in AF + WPW