367.3 🏥 內科專科考前版

367.3.1 Mechanistic Deep Dive

367.3.1.1 Bezold-Jarisch Reflex

  • Vasovagal mechanism
  • Vigorous ventricular contraction → mechanoreceptor stimulation
  • Vagal output → bradycardia + vasodilation

367.3.1.2 Orthostatic Physiology

  • Standing → 500-700 mL pool in legs
  • Normal: baroreflex → ↑ HR, ↑ NE
  • Failure: orthostatic hypotension

367.3.1.3 Inherited Arrhythmia Syndromes

Long QT Syndrome (LQTS): - 15+ subtypes - LQT1 (KCNQ1) — exertion/swimming - LQT2 (KCNH2) — emotion/auditory - LQT3 (SCN5A) — sleep/rest - Torsades de pointes - β-blocker + ICD

Brugada Syndrome: - SCN5A - Type 1 coved ST elevation V1-V3 - Sleep/rest syncope - Asian male predominant - ICD if symptomatic

CPVT (Catecholaminergic Polymorphic VT): - RyR2, CASQ2 - Exercise-induced bidirectional VT - β-blocker + ICD + flecainide

ARVC (Arrhythmogenic Right Ventricular Cardiomyopathy): - Multiple desmosomal genes - Epsilon waves - T-wave inversion V1-V3 - ICD

Short QT Syndrome: rare

367.3.1.4 Implantable Loop Recorder (ILR)

  • Inserted SC
  • 3-year battery
  • Continuous monitoring
  • For recurrent unexplained syncope after negative workup
  • High diagnostic yield (~ 50%)

367.3.2 Recent Trials & Updates

367.3.2.1 POST IV Trial (2020)

  • Atomoxetine for vasovagal — modest benefit

367.3.2.2 ASSURE (2023)

  • ILR vs conventional for unexplained syncope
  • ILR superior diagnostic yield

367.3.2.3 Atomoxetine for OH (2018)

  • Effective for orthostatic hypotension

367.3.2.4 Droxidopa (Northera) FDA 2014

  • Symptomatic neurogenic OH in PD, PAF, MSA
  • Converts to NE

367.3.2.5 Wearable ECG Monitors

  • Smart watches (Apple, Fitbit)
  • Detect AF
  • Patches (Zio)

367.3.3 High-Yield Specialist Points

367.3.3.1 Pseudosyncope

  • Repeated apparent LOC
  • No hemodynamic changes
  • Tilt test reproduces
  • Psychogenic

367.3.3.2 Convulsive Syncope

  • Brief myoclonic jerks during syncope
  • Common, benign
  • Distinguished from seizure by context, brevity, no post-ictal

367.3.3.3 Atrial Myxoma

  • “Ball-valve” effect
  • Positional syncope
  • Echocardiogram
  • Surgical removal

367.3.3.4 Subclavian Steal

  • Stenosis proximal subclavian → flow reversal in vertebral
  • Arm exercise → vertebrobasilar symptoms (syncope rare)
  • B/L BP difference

367.3.3.5 Pulmonary HTN Syncope

  • Exertional
  • Right heart failure
  • ECG: RV strain
  • Echo

367.3.3.6 Aortic Dissection

  • Tearing chest/back pain
  • Syncope from tamponade or hypotension
  • B/L BP difference, new AR murmur

367.3.3.7 Massive PE

  • Exertional dyspnea + syncope
  • Tachycardia, hypotension
  • D-dimer, CTA

367.3.3.8 Pacemaker Syndrome

  • VVI pacing → AV dissociation → cardiac output ↓ + syncope
  • Treatment: upgrade to dual-chamber

367.3.3.9 Heart Block with Syncope

  • Mobitz II
  • Complete heart block
  • Pacemaker indication

367.3.3.10 Vasovagal vs POTS

  • Vasovagal: ↓ BP, ↓ HR, brief LOC
  • POTS: ↑ HR without BP drop, no LOC (presyncope)

367.3.4 Pearls

  • Three categories: reflex, orthostatic, cardiac (most concerning)
  • ECG mandatory for all syncope
  • Echo if structural
  • Holter / loop recorder for arrhythmia suspected
  • ILR for recurrent unexplained
  • Tilt table for reflex/POTS
  • Carotid sinus massage for older with carotid sinus syndrome
  • Channelopathies: LQTS, Brugada, CPVT, ARVC
  • Pacemaker for bradyarrhythmias
  • ICD for high-risk VT/structural
  • Midodrine, fludrocortisone, droxidopa for OH