263.1 🎓 醫孞生版

263.1.0.1 📌 䞀頁重點

263.1.0.1.1 Bradycardia Defined
  • Heart rate < 60 bpm
  • May be physiologic (athletes, sleep) or pathologic
263.1.0.1.2 Sinus Node Dysfunction (SND)
263.1.0.1.2.1 Sinus Bradycardia
  • HR < 60 bpm
  • Causes:
    • Physiologic: athletes, sleep, vagal tone
    • Drugs: β-blockers, CCB (non-dihydropyridine), digoxin, amiodarone, ivabradine, antiarrhythmics
    • Hypothyroidism
    • Hypothermia
    • ↑ ICP
    • Inferior MI (RCA disease — vagal stimulation)
    • Sick sinus syndrome (SSS) — degenerative
263.1.0.1.2.2 Sinus Pauses / Arrest
  • Failure of sinus node to depolarize
  • Sometimes physiologic
  • Can be symptomatic (syncope, presyncope)
263.1.0.1.2.3 Sick Sinus Syndrome (SSS) / Sinoatrial Node Dysfunction
  • Spectrum:
    • Inappropriate sinus bradycardia
    • Sinus arrest
    • Sinoatrial exit block
    • Chronotropic incompetence (inability to ↑ HR with exercise)
    • Tachy-brady syndrome: alternating bradycardia (sinus pauses) + tachycardia (AF / atrial flutter)
  • Etiology: degenerative SAN, ischemia, infiltrative, drugs
  • Often elderly
  • Causes syncope, fatigue, exercise intolerance, palpitations
  • Workup: ECG, Holter, exercise test (chronotropic incompetence)
  • Treatment: pacemaker for symptomatic
263.1.0.1.3 AV Blocks
263.1.0.1.3.1 1° AV Block
  • PR > 200 ms (uniform delay)
  • Every P followed by QRS
  • Usually benign (no treatment needed unless very long or with structural disease)
  • Causes: athletes, drugs (BB, CCB, digoxin, amiodarone), age, ischemia
  • May progress to higher-degree block
263.1.0.1.3.2 2° Mobitz Type I (Wenckebach)
  • Progressive PR prolongation → dropped QRS (then resets)
  • Block at AV node (level above His)
  • Usually benign (esp asymptomatic, no syncope)
  • Causes: athletes, ↑ vagal tone, drugs, inferior MI
  • Treatment: usually none; pacemaker if symptomatic
  • Often improves with atropine
263.1.0.1.3.3 2° Mobitz Type II
  • Constant PR + intermittent dropped QRS (without warning)
  • Block at His-Purkinje level (infranodal)
  • Often diseased His-Purkinje system
  • High risk of progression to complete AV block
  • Pacemaker often indicated
  • Atropine may worsen (paradoxically) — increases atrial rate without proportional AV conduction
263.1.0.1.3.4 High-Grade AV Block
  • 2:1, 3:1, etc. block
  • Mobitz I or II nature variable
  • Distinguish with Holter, drugs, exercise
263.1.0.1.3.5 3° (Complete) AV Block
  • AV dissociation — atrial + ventricular rhythms independent
  • Atrial rate > ventricular rate
  • Escape rhythm: junctional (40-60 bpm) or ventricular (20-40 bpm)
  • Cannon a-waves on JVP
  • Causes: degenerative conduction system disease, congenital, ischemia, infiltrative
  • Pacemaker indicated for almost all (unless transient + correctable cause)
263.1.0.1.4 Pacemaker Indications (2024 ACC/AHA/ESC)
263.1.0.1.4.1 Class I (Strong)
  • Symptomatic bradycardia (sinus or AV block)
  • 2° Mobitz II or 3° AV block (acquired)
  • Symptomatic SSS
  • AV block after MI (persistent)
  • Asymptomatic complete AV block (some indications)
  • Carotid sinus hypersensitivity with recurrent syncope
  • Post-cardiac surgery permanent AV block
263.1.0.1.4.2 Class IIa
  • Asymptomatic 2° Mobitz II
  • Recurrent neurally-mediated syncope with bradycardia
263.1.0.1.4.3 Selected Indications
  • Bifascicular block + syncope (workup needed)
  • Drug-related bradycardia that can’t be discontinued
  • Hypertrophic cardiomyopathy (rare)
263.1.0.1.5 Pacemaker Types
263.1.0.1.5.1 Single Chamber
  • Ventricular only (VVI) or atrial only (AAI)
  • Chronic AF often gets VVI
263.1.0.1.5.2 Dual Chamber
  • DDD (atrial + ventricular sensing + pacing + AV synchrony)
  • Maintains AV synchrony
  • Standard for normal sinus rhythm with AV block
263.1.0.1.5.3 Biventricular (Cardiac Resynchronization Therapy — CRT)
  • Pacing right + left ventricle simultaneously
  • For HFrEF with LBBB + QRS > 130 ms + symptomatic
  • Improves outcomes (CARE-HF, MADIT-CRT)
263.1.0.1.5.4 Implantable Cardioverter Defibrillator (ICD)
  • For ventricular arrhythmia prevention
  • Often combined with pacing (DDD-ICD)
263.1.0.1.5.5 Leadless Pacemakers (2024 Update)
  • Micra (Medtronic, FDA 2016): single chamber VVI
  • Aveir (Abbott, FDA 2022): single chamber + dual chamber in development
  • No leads = no lead-related complications
  • Implanted in RV via catheter
  • Increasing adoption
263.1.0.1.5.6 Conduction System Pacing (2024 Update)
  • His-bundle pacing (HBP): paces His bundle for normal sequenced conduction
  • Left bundle branch area pacing (LBBAP): emerging alternative
  • More physiologic than RV apical pacing
  • Reduces pacing-induced cardiomyopathy
  • Increasing use, especially for high pacing burden + LV dysfunction
263.1.0.1.5.7 MRI-Conditional Pacemakers
  • Modern pacemakers MRI-safe under specific conditions
  • 1.5T or 3T MRI possible with most modern pacemakers
  • Cardiology / pacemaker representative coordination

263.1.0.2 1⃣ Sinus Node Dysfunction Detail

263.1.0.2.1 Causes
  • Idiopathic / degenerative (most common; elderly)
  • Ischemia (RCA disease)
  • Infiltrative (amyloidosis, sarcoidosis, hemochromatosis)
  • Inflammatory (myocarditis)
  • Trauma + surgical
  • Drugs: BB, CCB (verapamil, diltiazem), digoxin, amiodarone, lithium, ivabradine
  • Hypothyroidism
  • Hypothermia
263.1.0.2.2 Clinical
  • Symptomatic bradycardia: fatigue, exercise intolerance, dizziness, presyncope, syncope, dyspnea
  • Tachy-brady syndrome: palpitations + presyncope
  • Heart failure symptoms if chronotropic incompetence
  • Cognitive impairment in elderly
263.1.0.2.3 Workup
  • ECG, Holter monitor, event monitor
  • Exercise stress test (chronotropic incompetence — failure to achieve > 80% predicted max HR)
  • Electrophysiology study (rarely needed)
  • Drugs review + withdraw if possible
263.1.0.2.4 Treatment
  • Reversible causes: correct (stop drugs, treat hypothyroidism, etc.)
  • Symptomatic SSS: pacemaker (DDD or AAI)
  • Tachy-brady: pacemaker for bradycardia + medical / ablation for tachycardia
  • Chronotropic incompetence: rate-responsive pacemaker

263.1.0.3 2⃣ AV Block Detail

263.1.0.3.1 1° AV Block
  • PR > 200 ms
  • Each P followed by QRS
  • Usually benign
  • No treatment unless very long (> 300 ms — “marked”) + symptoms or structural disease
263.1.0.3.2 2° AV Block
263.1.0.3.2.1 Mobitz I (Wenckebach)
  • Progressive PR prolongation → dropped beat
  • Then resets
  • Block above His-Purkinje (at AV node typically)
  • Atropine improves (responds to vagal blockade)
  • Often benign + asymptomatic
  • Common in athletes, sleep
  • Treatment: usually none
263.1.0.3.2.2 Mobitz II
  • Constant PR + dropped beats
  • Block below AV node (His-Purkinje / infranodal)
  • Diseased Purkinje system
  • Atropine doesn’t improve (or worsens)
  • High risk of progression to complete AV block
  • Pacemaker often indicated
263.1.0.3.2.3 High-Grade AV Block
  • 2:1, 3:1 conduction
  • Can be Mobitz I or II
  • Distinction with longer rhythm strip + drug provocation (atropine, exercise)
263.1.0.3.3 3° Complete AV Block
  • No P → QRS conduction at all
  • AV dissociation
  • Atrial rate > ventricular rate
  • Escape rhythm:
    • Junctional (40-60 bpm, narrow QRS) — block at AV node level
    • Ventricular (20-40 bpm, wide QRS) — block below AV node
  • Causes: degenerative, congenital, ischemia, drug, infiltrative
  • Pacemaker indicated for almost all (unless transient + correctable cause like inferior MI with vagal stimulation)
263.1.0.3.4 Bifascicular + Trifascicular Block
  • Bifascicular = RBBB + LAFB or LPFB
  • Trifascicular = bifascicular + 1° AV block (variable definition)
  • Risk of progression to complete AV block
  • Workup if symptomatic (Holter, EP study)
  • Pacemaker for symptomatic

263.1.0.4 3⃣ Pacemaker Indications

263.1.0.4.1 Class I (Strong) ACC/AHA/ESC
263.1.0.4.1.1 Sinus Node Dysfunction
  • Symptomatic bradycardia or chronotropic incompetence
  • Drug-induced bradycardia where drug can’t be discontinued
  • Symptomatic sinus pauses ≥ 3 seconds
263.1.0.4.1.2 AV Block
  • 2° Mobitz II, especially with bundle branch block
  • 3° AV block (acquired)
  • Symptomatic complete AV block (any escape rate)
  • Asymptomatic complete AV block with average HR < 40 bpm
  • Pauses ≥ 3 sec
  • AV block + ventricular arrhythmia
  • Post-MI AV block (persistent)
263.1.0.4.1.3 Special
  • Carotid sinus hypersensitivity with recurrent syncope + asystole
  • Bifascicular block + syncope (after EP study)
263.1.0.4.2 Pacemaker Modes (Coding)
263.1.0.4.2.1 NBG / NASPE-BPEG Code (5-Letter)
  1. First: chamber paced (A, V, D)
  2. Second: chamber sensed (A, V, D, O)
  3. Third: response (I = inhibit, T = trigger, D = dual)
  4. Fourth: rate responsiveness (R)
  5. Fifth: multisite pacing
263.1.0.4.2.2 Common Modes
  • VVI: ventricular paced, ventricular sensed, inhibits on sense
  • AAI: atrial paced, atrial sensed, inhibits
  • DDD: dual chamber paced + sensed + dual response (most common in normal sinus rhythm with AV block)
  • DDDR: dual chamber + rate responsive
  • VVIR: ventricular + rate responsive (often used in chronic AF)
263.1.0.4.3 Choose by Patient
  • Chronic AF: VVI (no atrial activity to sense)
  • Sinus rhythm + AV block: DDD (maintains AV synchrony)
  • SSS without AV block: AAI (atrial only)
  • Chronotropic incompetence: rate-responsive

263.1.0.5 4⃣ Pacemaker Procedure + Complications

263.1.0.5.1 Procedure
  • IV access + conscious sedation + local anesthesia
  • Pectoral pocket created
  • Lead(s) advanced via subclavian / cephalic vein to chamber
  • Generator connected
  • Testing + final implantation
263.1.0.5.2 Common Complications
263.1.0.5.2.1 Acute
  • Hematoma (1-5%)
  • Pneumothorax (subclavian access)
  • Cardiac perforation (rare)
  • Lead dislodgement
  • Infection (rare with appropriate antibiotics + technique)
263.1.0.5.2.2 Long-Term
  • Lead failure (over years)
  • Twiddler’s syndrome (patient rotates generator → lead displacement)
  • Pacemaker syndrome: ventricular pacing causing reverse atrial contraction → fatigue, palpitations, hypotension; managed by upgrade to dual chamber
  • Generator infection (rare; sometimes leads to extraction)
263.1.0.5.3 Battery Life
  • Typically 8-15 years
  • Generator replacement procedure
263.1.0.5.4 Antibiotic Prophylaxis
  • For implantation procedures
  • Some guidelines for dental procedures (controversial — IDSA 2024 minimizes)

263.1.0.6 5⃣ Modern Innovations (2024)

263.1.0.6.1 Leadless Pacemakers
  • Micra (Medtronic, FDA 2016): single-chamber VVI; placed in RV via femoral catheter
  • Aveir (Abbott, FDA 2022): single-chamber + dual-chamber in development (paired)
  • Advantages:
    • No lead-related complications
    • No pocket needed (cosmetic)
    • Reduced infection risk
  • Limitations:
    • Currently single chamber only (Aveir dual in development)
    • Higher cost
    • Limited rescue if dysfunction
263.1.0.6.2 Conduction System Pacing
263.1.0.6.2.1 His Bundle Pacing (HBP)
  • Pace directly at His bundle
  • More physiologic than RV apex pacing
  • Reduces pacing-induced cardiomyopathy
  • Indicated for high pacing burden, AV block + reduced LV function
263.1.0.6.2.2 Left Bundle Branch Area Pacing (LBBAP)
  • Emerging alternative
  • Easier procedure than HBP
  • Similar physiologic benefits
  • Increasing adoption 2024+
263.1.0.6.3 Cardiac Resynchronization Therapy (CRT)
  • Biventricular pacing for HFrEF with LBBB + symptomatic (NYHA II-III) + QRS > 130 ms
  • Improves mortality + symptoms (CARE-HF, MADIT-CRT)
  • Standard of care in selected HFrEF
263.1.0.6.4 MRI-Conditional Pacemakers
  • Modern devices MRI-safe under specific conditions
  • 1.5T or 3T compatibility
  • Cardiology + radiology coordination
263.1.0.6.5 Smart Devices
  • Apple Watch / wearables for AF detection
  • ILR (implantable loop recorder) for cryptogenic
  • Increasing data integration