264.1 🎓 醫孞生版

264.1.0.1 📌 䞀頁重點

264.1.0.1.1 Definition
  • Heart rate > 100 bpm + narrow QRS (< 120 ms typically)
  • Originates above ventricles (atria + AV junction)
  • Distinct from sinus tachycardia (physiologic)
264.1.0.1.2 Major SVT Types
264.1.0.1.2.1 Sinus Tachycardia
  • Compensatory (fever, hypovolemia, anemia, pain, exercise, hyperthyroidism, drugs, anxiety, sepsis)
  • Pathologic: inappropriate sinus tachycardia, POTS
  • Gradual onset/offset
264.1.0.1.2.2 Atrial Fibrillation (AF)
  • Most common sustained arrhythmia (Ch 264 dedicated)
  • Irregularly irregular
  • No P waves
264.1.0.1.2.3 Atrial Flutter (AFL)
  • “Saw-tooth” pattern (esp II, III, aVF)
  • Atrial rate ~ 300 bpm
  • Often 2:1 conduction → ventricular rate 150
  • Treatment: cavotricuspid isthmus ablation (typical, counterclockwise) very effective
264.1.0.1.2.4 Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
  • Most common paroxysmal SVT (~ 60%)
  • Slow + fast pathway in AV node
  • Re-entry within AV node
  • Regular narrow complex; rate 150-220
  • Retrograde P often hidden in QRS or just after (pseudo-S in II, III, aVF; pseudo-R’ in V1)
  • Sudden onset / offset
264.1.0.1.2.5 Atrioventricular Reentrant Tachycardia (AVRT)
  • Accessory pathway-mediated (WPW)
  • Macro re-entry circuit (AV node + accessory pathway)
  • Orthodromic (~95%): conducts down AV node + up accessory pathway → narrow QRS
  • Antidromic (~5%): conducts down accessory pathway + up AV node → wide QRS (mimics VT)
  • WPW on baseline ECG (short PR + delta wave + wide QRS) when not in SVT
264.1.0.1.2.6 Atrial Tachycardia (AT)
  • Focal automaticity (atrial focus other than SAN)
  • Variable P wave morphology (different from sinus P)
  • Multiple foci: multifocal AT (≥ 3 P morphologies — often COPD, electrolytes)
  • May or may not respond to adenosine
  • Sometimes warm-up phenomenon (gradual rate increase)
264.1.0.1.2.7 Junctional Tachycardia
  • Originates in AV junction
  • HR usually 60-130 (junctional rate)
  • AV dissociation possible
  • Often digoxin toxicity, post-cardiac surgery
264.1.0.1.3 Acute Management
264.1.0.1.3.1 Stable Patient
  1. Vagal maneuvers: Valsalva, modified Valsalva (REVERT trial — better), carotid sinus massage
  2. Adenosine 6 mg IV rapid push → 12 mg if needed → may give 18 mg
  3. Calcium channel blocker IV (verapamil, diltiazem) for AVNRT, AVRT (not WPW+AF)
  4. β-blocker IV alternative
  5. Cardioversion if unstable (synchronized)
264.1.0.1.3.2 Unstable Patient (Hypotension, Chest Pain, Pulmonary Edema, Altered Mental Status)
  • Synchronized cardioversion (50-100 J biphasic)
264.1.0.1.3.3 Antidromic AVRT (Wide-Complex SVT)
  • Treat as VT until proven otherwise
  • Procainamide IV
  • Avoid AV nodal blockers (worsens — accessory pathway becomes only route)
264.1.0.1.3.4 WPW + AF (Pre-Excited AF) — Special Caution
  • Avoid AV nodal blockers (BB, CCB, digoxin, adenosine)
  • Reason: blocks AV node → accessory pathway conducts unimpeded → very rapid ventricular response → may degenerate to VF
  • Procainamide IV or cardioversion preferred
264.1.0.1.4 Chronic Management
264.1.0.1.4.1 Recurrent Symptomatic SVT
  • Catheter ablation = curative for AVNRT, AVRT, AFL, AT, idiopathic SVT
  • Success rate > 95% for AVNRT + typical AFL; > 90% AVRT
  • Outpatient procedure (4-6 hr typically)
  • Reduces / eliminates antiarrhythmic drug use
264.1.0.1.4.2 Drug Therapy (Alternative to Ablation)
  • β-blockers (first-line for many)
  • Calcium channel blockers (verapamil, diltiazem)
  • Flecainide (for refractory; avoid in structural heart disease)
  • Propafenone (similar)
  • Amiodarone (last resort due side effects)
264.1.0.1.4.3 WPW Management
  • Catheter ablation of accessory pathway = curative + standard for symptomatic
  • Asymptomatic WPW: risk stratification (younger high-risk preference for ablation)
264.1.0.1.5 Specific Conditions
264.1.0.1.5.1 Multifocal Atrial Tachycardia (MAT)
  • ≥ 3 different P morphologies
  • COPD, hypoxia, electrolyte abnormalities
  • Treat underlying (oxygen, bronchodilators, K+, Mg2+)
  • IV magnesium, β-blockers (caution in COPD), CCB
264.1.0.1.5.2 Inappropriate Sinus Tachycardia
  • Resting HR > 90 bpm with no obvious cause
  • Often young women
  • POTS (Postural Orthostatic Tachycardia Syndrome) — orthostatic increase > 30 bpm
  • Treatment: lifestyle, ivabradine, beta-blocker

264.1.0.2 1⃣ ECG Approach to Narrow Complex Tachycardia

264.1.0.2.1 Step 1: Regular vs Irregular
  • Irregular: AF, atrial flutter with variable block, MAT
  • Regular: AVNRT, AVRT, atrial flutter (constant block), AT, junctional, sinus tachycardia
264.1.0.2.2 Step 2: P-Wave Analysis
264.1.0.2.2.1 Visible P Before Each QRS
  • Sinus tachycardia (P normal morphology)
  • Atrial tachycardia (P abnormal morphology)
  • Atrial flutter with 1:1 conduction (rare)
264.1.0.2.2.2 No Visible P or P Hidden
  • AVNRT typical (retrograde P hidden in QRS or just after)
  • Junctional tachycardia
264.1.0.2.2.3 Inverted P (Retrograde)
  • AVNRT, AVRT (retrograde conduction)
264.1.0.2.2.4 Multiple P Morphologies
  • MAT (≥ 3 morphologies)
264.1.0.2.3 Step 3: Response to Adenosine
  • Sinus tachycardia: gradual slowing
  • AVNRT: terminates (often)
  • AVRT: terminates (often)
  • Atrial flutter / AT: unmasks flutter waves / no termination but slows ventricular response (transient)
  • Sinus: gradual slowing
  • MAT: no termination but slows
264.1.0.2.4 Step 4: Other Features
  • Onset / offset (sudden vs gradual)
  • Provocation factors
  • Family history
  • Baseline ECG (WPW pattern?)

264.1.0.3 2⃣ AVNRT (AV Nodal Reentry Tachycardia)

264.1.0.3.1 Mechanism
  • Slow pathway + fast pathway in AV node (dual AV nodal physiology)
  • Typical AVNRT (90%): slow path antegrade + fast path retrograde — atrial activation simultaneous with ventricular
  • Atypical AVNRT (10%): fast path antegrade + slow path retrograde
  • Re-entry circuit within AV node
264.1.0.3.2 Clinical
  • Sudden onset palpitations
  • Often young + middle-age women (3:1 women:men)
  • Rate 150-220
  • Triggered by ectopic beats, stress, caffeine, exercise
  • Self-limited or terminated with vagal maneuver / adenosine
264.1.0.3.3 ECG
  • Regular narrow complex tachycardia
  • No discrete P waves (often hidden in QRS or just after — pseudo-S in II, III, aVF or pseudo-R’ in V1)
  • Rate 150-220
264.1.0.3.4 Acute Management
  1. Vagal maneuvers (Valsalva or modified Valsalva — REVERT trial; carotid sinus massage)
  2. Adenosine 6 mg IV rapid push → 12 mg if needed
  3. IV calcium channel blocker (verapamil, diltiazem) alternative
  4. IV β-blocker
  5. Cardioversion if unstable
264.1.0.3.5 Chronic / Recurrent
  • Catheter ablation = first-line for symptomatic recurrent (success > 95%, complications < 1%)
  • Targets slow pathway
264.1.0.3.6 Catheter Ablation
  • Slow pathway modification (preferred — preserves AV node)
  • Outpatient
  • Major complications: AV block requiring pacemaker (1%)

264.1.0.4 3⃣ AVRT (AV Reciprocating Tachycardia / WPW)

264.1.0.4.1 Mechanism
  • Accessory pathway (Bundle of Kent) connecting atria + ventricles outside AV node
  • Re-entry circuit using AV node + accessory pathway
264.1.0.4.1.1 Orthodromic AVRT (~ 95%)
  • Antegrade conduction: AV node → ventricle → accessory pathway retrograde
  • Narrow QRS during tachycardia
  • P wave after QRS (retrograde)
264.1.0.4.1.2 Antidromic AVRT (~ 5%)
  • Antegrade conduction: accessory pathway → ventricle → AV node retrograde
  • Wide QRS during tachycardia (resembles VT)
  • Treat as VT until proven otherwise
264.1.0.4.2 Wolff-Parkinson-White (WPW) Syndrome
  • Pre-excitation pattern on baseline ECG:
    • Short PR (< 120 ms)
    • Delta wave (slurred upstroke of QRS)
    • Wide QRS (> 110 ms)
  • Conduction down accessory pathway preempts AV node
264.1.0.4.3 Acute AVRT Management
264.1.0.4.3.1 Orthodromic (Narrow QRS)
  • Vagal maneuvers + adenosine + AV nodal blockers (similar to AVNRT)
264.1.0.4.3.2 Antidromic (Wide QRS)
  • Treat as VT until proven otherwise
  • Procainamide IV (slows accessory pathway)
  • Cardioversion if unstable
264.1.0.4.3.3 Pre-Excited AF (WPW + AF)
  • AVOID AV nodal blockers (BB, CCB, digoxin, adenosine)
  • Rationale: blocking AV node leaves accessory pathway → very rapid ventricular response
  • May degenerate to VF
  • Procainamide IV or cardioversion preferred
264.1.0.4.4 Chronic Management
  • Catheter ablation of accessory pathway = curative + standard for symptomatic
  • Success > 95%
  • Risk stratification for asymptomatic WPW:
    • Younger, athletic, high-risk occupation → consider ablation
    • EP study + risk assessment of accessory pathway refractoriness
264.1.0.4.5 Risk Stratification — Sudden Death Risk in WPW
  • Short refractory period of accessory pathway (< 250 ms)
  • Multiple accessory pathways
  • Septal location
  • Familial AVRT
  • Symptomatic (palpitations, syncope, AF)
  • Lowest risk: asymptomatic adults > 35 yr with no concerning features

264.1.0.5 4⃣ Atrial Flutter (AFL)

264.1.0.5.1 Mechanism
  • Macro-reentry circuit in atria
  • Typical (counterclockwise): cavotricuspid isthmus circuit (right atrium); negative flutter waves in II, III, aVF + positive in V1
  • Atypical: various circuits
264.1.0.5.2 ECG
  • Saw-tooth pattern (most evident II, III, aVF)
  • Atrial rate ~ 300 bpm
  • Often 2:1 AV conduction → ventricular rate ~ 150 bpm
  • 3:1 (rate 100) or 4:1 (rate 75) also seen
  • Variable conduction → irregular ventricular response
264.1.0.5.3 Acute Management
  • Vagal maneuvers + adenosine (slows AV conduction, unmasks flutter waves)
  • IV β-blocker or CCB (rate control)
  • Cardioversion if unstable
  • Cardioversion + anticoagulation considerations (similar to AF)
264.1.0.5.4 Chronic Management
  • Cavotricuspid isthmus ablation = highly effective for typical atrial flutter (> 95% success)
  • Antiarrhythmic alternative
  • Rate control (β-blocker, CCB) + anticoagulation (CHA2DS2-VASc)
264.1.0.5.5 Anticoagulation
  • Same principles as AF
  • CHA2DS2-VASc score for stroke risk

264.1.0.6 5⃣ Atrial Tachycardia (AT)

264.1.0.6.1 Mechanism
  • Focal automaticity (atrial focus other than SAN)
  • May respond to / not respond to adenosine (depends on mechanism)
  • Atrial rate typically 100-250
264.1.0.6.2 ECG
  • P wave morphology different from sinus
  • P-P regular usually
  • Sometimes “warm-up phenomenon” (gradual rate increase)
264.1.0.6.3 Multifocal Atrial Tachycardia (MAT)
  • ≥ 3 different P morphologies
  • COPD common, hypoxia, theophylline, hypokalemia, hypomagnesemia
  • Irregular rhythm
  • Treatment: oxygen, treat COPD, correct electrolytes, IV magnesium, β-blocker (caution in COPD)
264.1.0.6.4 Sustained Atrial Tachycardia
  • Catheter ablation if symptomatic
  • β-blocker / CCB / antiarrhythmics

264.1.0.7 6⃣ Vagal Maneuvers + Adenosine

264.1.0.7.1 Vagal Maneuvers
264.1.0.7.1.1 Valsalva Maneuver
  • Sustained expiratory effort against closed glottis
  • ~ 25% effective alone
264.1.0.7.1.2 Modified Valsalva (REVERT Trial)
  • Standard Valsalva + leg elevation immediately after
  • More effective (43% vs 17% standard)
  • Become first-line vagal maneuver
264.1.0.7.1.3 Carotid Sinus Massage
  • Unilateral, 5-10 seconds
  • Risk: stroke (elderly with carotid disease)
  • Auscultate for bruit first
  • Avoid in significant carotid disease
264.1.0.7.2 Adenosine
264.1.0.7.2.1 Dose
  • 6 mg IV rapid push (followed by saline flush) → if no response in 2 min:
  • 12 mg IV → if no response:
  • 18 mg IV (some protocols)
264.1.0.7.2.2 Mechanism
  • Brief AV node block
  • Terminates re-entrant SVT (AVNRT, AVRT)
  • Unmasks atrial activity in flutter / AT
264.1.0.7.2.3 Side Effects
  • Transient: flushing, chest pain, dyspnea, bradycardia/asystole (brief), bronchospasm (avoid in severe asthma)
  • AF triggered occasionally
  • Wide-complex / pre-excited AF — avoid
264.1.0.7.2.4 Avoid
  • Wide-complex SVT (use procainamide or cardioversion)
  • WPW + AF (pre-excited AF)
  • Severe asthma (bronchospasm)
  • 2° or 3° AV block (worsens)
  • Allergy

264.1.0.8 7⃣ Catheter Ablation

264.1.0.8.1 Indications
  • Recurrent symptomatic SVT
  • WPW (especially symptomatic or high-risk)
  • AF (Ch 264)
  • VT in select cases (Ch 265)
  • Atrial flutter
  • Atrial tachycardia
  • Idiopathic VT
264.1.0.8.2 Procedure
  • Femoral venous access
  • Catheters to right atrium → cross to left if needed (PFO or transseptal puncture)
  • 3D mapping system (EnSite, CARTO)
  • Radiofrequency or cryoablation
  • 4-6 hours typically
  • Outpatient or 1-day observation
264.1.0.8.3 Success Rates
  • AVNRT: > 95%
  • Typical AFL: > 95%
  • AVRT (WPW): > 95%
  • AF: 70-90% (paroxysmal); lower for persistent
  • Idiopathic VT: 80-90%
  • Scar-mediated VT: 60-80%
264.1.0.8.4 Complications
  • Bleeding / vascular access
  • AV block (especially AVNRT — slow pathway ablation; < 1% requiring pacemaker)
  • Cardiac perforation / tamponade (rare)
  • Atrial-esophageal fistula (AF ablation; rare but fatal)
  • Stroke (rare)