266.1 🎓 醫學生版

266.1.0.1 📌 一頁重點

266.1.0.1.1 Spectrum

266.1.0.1.1.1 Premature Ventricular Contractions (PVCs)

• Ectopic ventricular beats
• Usually benign in healthy
• Frequent / multifocal / R-on-T can be precursor to VT/VF
• Treatment: usually none; β-blocker if symptomatic; ablation if frequent + symptomatic + LV dysfunction (PVC-induced cardiomyopathy)

266.1.0.1.1.2 Non-Sustained VT (NSVT)

• ≥ 3 consecutive ventricular beats
• < 30 seconds
• Often asymptomatic
• Significance varies by clinical context

266.1.0.1.1.3 Sustained VT

• 30 seconds duration OR hemodynamic compromise

• Monomorphic (uniform QRS) vs polymorphic (varying QRS — usually ischemic)
• Wide QRS > 120 ms typically
• AV dissociation possible

266.1.0.1.1.4 Ventricular Fibrillation (VF)

• Chaotic, no organized complexes
• No effective cardiac output → cardiac arrest
• Treatment: immediate defibrillation

266.1.0.1.1.5 Torsades de Pointes

• Polymorphic VT with QT prolongation
• “Twisting around baseline” appearance
• Acquired (drugs, electrolyte) or congenital LQTS
• Treatment: magnesium IV + isoproterenol or pacing + cause correction; defibrillation if sustained

266.1.0.1.2 Sudden Cardiac Death (SCD)

266.1.0.1.2.1 Definition

• Death within 1 hour of symptom onset
• ~ 50% of cardiovascular deaths
• ~ 7-9 million deaths/yr globally

266.1.0.1.2.2 Causes

• Ischemia + MI (60-80%)
• Structural heart disease (cardiomyopathy, HF)
• Channelopathies (LQTS, Brugada, CPVT, idiopathic VF)
• Commotio cordis (chest trauma during specific repolarization phase)
• Inflammatory (myocarditis)
• Aortic dissection / rupture
• PE

266.1.0.1.2.3 Survival

• Witnessed arrest with bystander CPR + AED — survival 30-50%
• Unwitnessed: < 10%

266.1.0.1.3 Implantable Cardioverter Defibrillator (ICD)

266.1.0.1.3.1 Secondary Prevention (Class I)

• Survivors of cardiac arrest from VF/VT (no reversible cause)
• Sustained hemodynamically unstable VT
• Sustained VT + structural heart disease

266.1.0.1.3.2 Primary Prevention (Class I/IIa)

• HFrEF EF ≤ 35% + NYHA II-III on optimal medical therapy (≥ 3 months) — MADIT-II, SCD-HeFT
• HCM with risk factors (family hx SCD, syncope, NSVT, LVH ≥ 30 mm, abnormal BP response, late gadolinium enhancement)
• Symptomatic LQTS + recurrent syncope despite β-blocker
• Brugada syndrome with prior cardiac arrest or syncope
• ARVC with high-risk features
• CPVT with recurrent VT despite β-blocker
• HFpEF + EF 35-50% + NSVT + inducible VT on EP study (some indications)

266.1.0.1.3.3 ICD Technology

• Transvenous ICD: traditional; lead through subclavian to RV
• Subcutaneous ICD (S-ICD): lead under skin (no transvenous lead); cannot pace
• Wearable cardioverter defibrillator (LifeVest): external; bridge to ICD or recovery

266.1.0.1.4 Acute Management

266.1.0.1.4.1 Pulseless VT / VF

• Immediate defibrillation (200 J biphasic)
• CPR
• Epinephrine 1 mg IV q3-5 min
• Amiodarone 300 mg IV bolus (for refractory)
• Lidocaine alternative
• Treat reversible causes (Hs and Ts)

266.1.0.1.4.2 Sustained VT with Pulse

• Stable: amiodarone IV, procainamide IV, lidocaine IV
• Unstable: synchronized cardioversion 100-200 J
• Magnesium for torsades

266.1.0.1.4.3 Polymorphic VT / Torsades

• Magnesium 2 g IV bolus + correct electrolytes (K, Ca)
• Withhold offending drugs
• Isoproterenol or temporary pacing for bradycardia-related
• Cardioversion / defibrillation if sustained / hemodynamically unstable

266.1.0.1.4.4 Acute Long QT (Torsades)

• Stop offending drugs
• Correct K + Mg + Ca
• Mag IV
• Isoproterenol or pacing if bradycardic

266.1.0.1.5 Channelopathies + Inherited Arrhythmia Syndromes

266.1.0.1.5.1 Long QT Syndrome (LQTS)

• Congenital types: LQT1 (KCNQ1), LQT2 (KCNH2), LQT3 (SCN5A) — most common
• Romano-Ward (autosomal dominant)
• Jervell-Lange-Nielsen (autosomal recessive + deafness)
• Triggers: exercise (LQT1), startle/loud noise (LQT2), sleep/rest (LQT3)
• Treatment:
  • β-blockers (first-line, except LQT3 — caution; some mexiletine + propranolol)
  • ICD if recurrent syncope/cardiac arrest despite β-blocker
  • Avoid QT-prolonging drugs

266.1.0.1.5.2 Brugada Syndrome

• ST elevation V1-V3 (Type 1 = coved; Type 2 = saddle-back)
• SCN5A mutations
• Risk of VF + SCD
• Treatment:
  • ICD for symptomatic or family hx SCD
  • Quinidine for storms
  • Avoid drugs that unmask Brugada (sodium channel blockers, propofol, others)
  • Avoid fever

266.1.0.1.5.3 Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

• Plakophilin-2, desmoplakin, other mutations
• Fibrofatty replacement of RV
• Risk of VT + SCD
• Treatment:
  • ICD
  • Exercise restriction
  • Antiarrhythmic drugs
  • β-blockers

266.1.0.1.5.4 Catecholaminergic Polymorphic VT (CPVT)

• RYR2 mutations
• Exercise-induced bidirectional VT
• Treatment:
  • β-blockers (nadolol typically)
  • Flecainide (calcium handling)
  • ICD if symptomatic despite drugs
  • Exercise restriction
  • Left cardiac sympathetic denervation for refractory

266.1.0.1.5.5 Hypertrophic Cardiomyopathy (HCM)

• See Ch 270
• Sudden cardiac death = leading cause of death in HCM
• Risk factors: family history SCD, syncope, NSVT, LVH ≥ 30 mm, abnormal BP response, late gadolinium enhancement on MRI
• ICD for high-risk

266.1.0.1.6 Catheter Ablation for VT

• Substrate-based mapping (scar from MI primarily)
• Idiopathic VT (RVOT origin most common, also LVOT, fascicular)
• Sustained monomorphic VT not responding to drugs
• Recurrent VT despite ICD shocks (ICD shock reduction)
• VT storm (refractory recurrent VT)

266.1.0.1.7 Familial Screening for SCD

• First-degree relatives of SCD victims
• ECG + echo + cardiac MRI + family history + genetic testing
• Channelopathies: family-based genetic + ECG screening

---

266.1.0.2 1️⃣ PVCs (Premature Ventricular Contractions)

266.1.0.2.1 Background

• Ectopic ventricular beats
• Common (40% of adults on Holter)
• Usually benign in healthy

266.1.0.2.2 Causes

• Idiopathic (most)
• Caffeine, alcohol, stress, fatigue
• Ischemia
• Electrolytes (hypokalemia, hypomagnesemia)
• Drugs (digoxin, antiarrhythmics, stimulants)
• Hyperthyroidism
• Structural heart disease

266.1.0.2.3 When to Worry

• Symptomatic (palpitations, presyncope)
• Frequent (> 10,000 / 24 hr or > 10% PVC burden) → may cause LV dysfunction (PVC-induced cardiomyopathy)
• Multifocal
• R-on-T phenomenon
• Couplets / triplets / NSVT
• Structural heart disease
• Family history SCD

266.1.0.2.4 Workup

• ECG
• Holter / event monitor (quantify burden)
• Echo (rule out structural)
• Stress test (rule out ischemia)
• Cardiac MRI if suspicion structural

266.1.0.2.5 Treatment

• Asymptomatic + benign: no treatment
• Symptomatic: β-blocker, calcium channel blocker
• PVC-induced cardiomyopathy: catheter ablation
• Idiopathic PVCs from RVOT/LVOT: catheter ablation curative
• Avoid triggers (caffeine, stimulants)

---

266.1.0.3 2️⃣ Sustained VT

266.1.0.3.1 Categories

266.1.0.3.1.1 Monomorphic VT

• Uniform QRS morphology
• Usually from re-entry circuit around scar (post-MI)
• More common in patients with ischemic cardiomyopathy
• Can also occur from non-ischemic cardiomyopathy

266.1.0.3.1.2 Polymorphic VT

• Varying QRS morphology
• Torsades de pointes if QT prolonged
• Acute ischemia (often)
• Hypokalemia, hypomagnesemia
• Drug-induced LQTS

266.1.0.3.1.3 Idiopathic VT

• Outflow tract VT (RVOT, LVOT) — usually monomorphic
• Fascicular VT (left posterior fascicle, verapamil-sensitive)
• Generally good prognosis
• Catheter ablation often curative

266.1.0.3.2 Wide-Complex Tachycardia Differential

266.1.0.3.2.1 Diagnosis Approach (Brugada Algorithm)

1. Absence of RS in all precordial leads → VT
2. R to S interval > 100 ms in any precordial lead → VT
3. AV dissociation → VT
4. Morphology criteria → VT vs aberrant SVT

266.1.0.3.3 Features Favoring VT (vs Aberrant SVT)

• Older age, structural heart disease, prior MI
• AV dissociation
• Capture / fusion beats
• Wide QRS (> 140 ms)
• Concordant precordial pattern
• Northwest axis (-90 to -180)

266.1.0.3.4 Treatment

266.1.0.3.4.1 Stable Sustained VT

• Procainamide IV (PROCAMIO trial — first choice over amiodarone)
• Amiodarone IV (alternative)
• Lidocaine IV (alternative; if ischemic)
• Cardioversion if drug failure

266.1.0.3.4.2 Unstable Sustained VT

• Synchronized cardioversion (100-200 J biphasic)
• Treat ischemia if cause

266.1.0.3.4.3 Refractory / Recurrent

• Beta-blocker (IV β-blocker; esmolol, propranolol — for sympathetic storm)
• Catheter ablation
• ECMO bridge if refractory

266.1.0.3.5 Reversible Causes (Hs and Ts)

266.1.0.3.5.1 Hs

• Hypoxia
• Hypovolemia
• Hydrogen (acidosis)
• Hyper/Hypokalemia
• Hypothermia

266.1.0.3.5.2 Ts

• Tension pneumothorax
• Tamponade
• Toxins
• Thrombosis (PE, MI)
• Trauma

---

266.1.0.4 3️⃣ Ventricular Fibrillation (VF) + Cardiac Arrest

266.1.0.4.1 Background

• Chaotic ventricular electrical activity
• No cardiac output
• Lethal within minutes without intervention
• Most common cause of SCD

266.1.0.4.2 Causes

• Acute ischemia + MI (most common in adults)
• Cardiomyopathy (HCM, DCM, ARVC)
• LV dysfunction (severe HFrEF)
• Channelopathies (LQTS, Brugada, CPVT)
• Electrolyte abnormalities (hypokalemia)
• Drug overdose / toxic
• Commotio cordis (chest trauma during specific repolarization)
• Post-cardiac surgery
• Severe HF / shock

266.1.0.4.3 Initial Response

• Immediate defibrillation (200 J biphasic)
• High-quality CPR
• Identify + treat reversible causes
• Hospital admission post-resuscitation

266.1.0.4.4 Post-Cardiac Arrest Care

• Targeted temperature management (33-36°C × 24 hr — controversial; some recommendation for fever avoidance only)
• Hemodynamic optimization
• Neurologic prognostication (delayed 72+ hours)
• Coronary angiography + PCI for suspected ischemic cause
• ICD post-discharge in survivors without reversible cause

---

266.1.0.5 4️⃣ Torsades de Pointes

266.1.0.5.1 Background

• Polymorphic VT with QT prolongation
• “Twisting around baseline” appearance
• Often self-terminates but can degenerate to VF

266.1.0.5.2 Causes

266.1.0.5.2.1 Congenital LQTS

• LQT1 (KCNQ1), LQT2 (KCNH2), LQT3 (SCN5A) most common

266.1.0.5.2.2 Acquired Long QT

• Drugs:
  • Antiarrhythmics (Ia, III): quinidine, sotalol, ibutilide, dofetilide, amiodarone (less often)
  • Antibiotics: macrolides, FQ
  • Antifungals: fluconazole, voriconazole
  • Antipsychotics: haloperidol, clozapine, ziprasidone, others
  • Antidepressants: TCAs, citalopram, escitalopram
  • Methadone
  • Ondansetron
  • Cisapride (withdrawn)
  • Other: cocaine, alcohol (some)
• Electrolytes: hypokalemia, hypomagnesemia, hypocalcemia
• Bradycardia
• MI / cardiac ischemia
• CNS event (stroke, hemorrhage)
• Hypothyroidism

266.1.0.5.3 Management

• Stop offending drugs (if acquired)
• Magnesium IV 2 g (1st-line)
• Correct electrolytes (K, Ca, Mg)
• Isoproterenol (increases HR, shortens QT)
• Temporary pacing (overdrive bradycardia)
• Lidocaine (alternative)
• Defibrillation if hemodynamically unstable / sustained

---

266.1.0.6 5️⃣ ICD (Implantable Cardioverter Defibrillator)

266.1.0.6.1 Components

• Generator (under chest wall)
• Lead(s) to right ventricle (transvenous ICD)
• Subcutaneous ICD has lead under skin (no transvenous)

266.1.0.6.2 Functions

• Continuous monitoring
• Detect VT/VF
• Anti-tachycardia pacing (ATP) for VT — painless, often effective
• Shock for sustained VT or VF
• Pacing function (backup bradycardia)

266.1.0.6.3 Primary Prevention Indications

266.1.0.6.3.1 HFrEF

• EF ≤ 35% + NYHA II-III on optimal medical therapy ≥ 3 months
• EF ≤ 30% + NYHA I (some indications)
• Ischemic + non-ischemic cardiomyopathy
• MADIT-II, SCD-HeFT trials

266.1.0.6.3.2 HCM

• Family history SCD < 50 yr
• Recent unexplained syncope
• NSVT on Holter
• LV wall thickness ≥ 30 mm
• Abnormal BP response to exercise
• Extensive late gadolinium enhancement on CMR

266.1.0.6.3.3 Channelopathies

• LQTS: recurrent syncope / cardiac arrest despite β-blockers
• Brugada: cardiac arrest, syncope, family hx SCD
• CPVT: recurrent syncope despite β-blocker / flecainide
• ARVC: high-risk features
• Short QT: cardiac arrest

266.1.0.6.4 Secondary Prevention

• Survivors of cardiac arrest (no reversible cause)
• Sustained hemodynamically unstable VT
• Sustained VT + structural heart disease

266.1.0.6.5 Complications

• Inappropriate shocks (sinus tachycardia, AF, oversensing) — distressing
• Lead failure
• Infection
• Battery depletion (5-10 yr)

266.1.0.6.6 Innovations

266.1.0.6.6.1 Subcutaneous ICD (S-ICD)

• No transvenous lead
• Useful in young patients, anatomic issues
• Cannot pace (anti-tachycardia pacing)

266.1.0.6.6.2 Wearable Cardioverter Defibrillator (LifeVest)

• External vest
• Bridge to ICD or recovery
• Post-MI (early period)
• New HF until reassessment

266.1.0.6.6.3 Subcutaneous + Leadless Innovation

• Newer technology emerging
• Combined leadless pacemaker + ICD (in development)

266.1.0.6.7 Decision-Making

• Patient preference essential
• Quality of life vs longevity
• Life expectancy
• Comorbidities
• Shock anxiety
• Driving restrictions (varies by jurisdiction)

---

266.1.0.7 6️⃣ Catheter Ablation for VT

266.1.0.7.1 Indications

• Sustained monomorphic VT (especially scar-mediated, post-MI)
• Idiopathic VT (RVOT, LVOT, fascicular)
• Recurrent VT despite ICD shocks (reduces shocks)
• VT storm (refractory recurrent)
• VT in non-ischemic cardiomyopathy

266.1.0.7.2 Technique

• 3D mapping (CARTO, EnSite)
• Substrate ablation (scar)
• Endocardial + epicardial approach
• Hemodynamic support during mapping (impella, ECMO) for tolerable

266.1.0.7.3 Success Rates

• Idiopathic VT: 80-90% single-procedure success
• Scar-mediated VT: 60-80%
• Multiple procedures sometimes needed

266.1.0.7.4 Risks

• Cardiac perforation / tamponade
• Stroke
• Procedural mortality 1-3%
• Recurrence common

---