Syncope Risk Stratification, Channelopathies [Brugada/LQTS/WPW] & Pacemaker/ICD Malfunctions

Triage, Defibrillator Pad Placement & 12-Lead ECG: Place patient on continuous cardiac monitor, pulse oximetry, and attach hands-free anteroposterior defibrillator/pacing pads if unstable bradycardia or polymorphic VT/VF. Obtain a 12-lead ECG within 2 minutes (plus high right precordial leads V1–V2 in the 2nd and 3rd intercostal spaces if Brugada suspected) [1,2,3].

Torsades de Pointes (TdP / Polymorphic VT with Long QT):
• Unstable / Pulseless: Immediate Unsynchronized Defibrillation (200 J biphasic) [3].
• First-Line Pharmacotherapy: Magnesium Sulfate (MgSO₄) 2 g (4 mL of 50% solution) IV push over 1–2 min (if pulseless) or over 10–15 min (if perfusing), followed by infusion at 1–2 g/hr [3,4].

Mg²⁺ blocks L-type calcium channels (Ca,L) during Phase 2 of the ventricular action potential, immediately suppressing Early Afterdepolarizations (EADs) regardless of baseline serum magnesium level [3,4].

Pre-Excited Atrial Fibrillation Override (WPW + AFib = Irregular Wide-Complex Tachycardia > 200–300 bpm): Differentiate from polymorphic VT. Check blood pressure and mentation immediately [3,5].

1. Unstable WPW + AFib: Immediate Synchronized Cardioversion (120–200 J biphasic) under Etomidate 0.15 mg/kg IV [3,5].
2. Stable WPW + AFib: Procainamide 15–17 mg/kg IV infused at 20–50 mg/min (or 100 mg IV q5min) until arrhythmia terminates, hypotension occurs, or QRS widens by > 50% (Max 1,000–1,500 mg), followed by 1–4 mg/min drip (or Ibutilide 1 mg IV over 10 min) [3,5].

Class IA/III sodium/potassium channel blockade prolongs the effective refractory period of the Accessory Pathway (Bundle of Kent) without blocking the AV node, preventing 1:1 conduction (300 bpm) and degeneration into Ventricular Fibrillation [3,5].

Pacemaker Failure to Capture / Failure to Output (Symptomatic Severe Bradycardia): Inspect chest wall for CIED generator pocket; apply transcutaneous pacing pads at least 8–10 cm away from the implanted generator (prefer anteroposterior position) [6,7].

Chronotropic Bridge & Transcutaneous Pacing: Start Epinephrine 2–10 mcg/min IV (2–10 mL/hr of 60 mcg/mL bag) or Isoproterenol 2–10 mcg/min IV [4,6]. Initiate Transcutaneous Pacing at 70–80 bpm, ramping current (mA) until both electrical and mechanical capture (confirmed by femoral pulse/POCUS/arterial line) are achieved + 10% safety margin [6,7].

Restores ventricular depolarization and cardiac output when pacemaker lead dislodgement, exit block, battery depletion, or oversensing causes asystole/profound bradycardia; check stat K⁺ (hyperkalemia causes acute exit block) [6,7].

Pacemaker-Mediated Tachycardia (PMT) OR Inappropriate ICD Shocks: Retrieve a clinical ring magnet (> 90 Gauss) from the crash cart and place it directly over the pacemaker or ICD generator pocket [6,7].

1. Pacemaker Magnet Response: Converts pacemaker from synchronous (DDD/VVI) to asynchronous pacing (DOO/VOO) at a fixed magnet rate (85–100 bpm), immediately breaking the PMT re-entrant loop or overriding electromagnetic/myopotential oversensing [6,7].
2. ICD Magnet Response: Suspends all tachyarrhythmia detection and defibrillation shocks while leaving bradycardia pacing completely unaffected [6,7].

Eliminates the retrograde atrial sensing arm of an endless-loop pacemaker-mediated tachycardia, or halts painful repetitive inappropriate ICD shocks caused by lead fracture, T-wave oversensing, or rapid AFib [6,7].

Brugada Electrical Storm vs. Pause-Dependent TdP Overdrive:
• Brugada Storm: Check core temperature and aggressively treat fever (> 37.5°C) [3].
• Refractory TdP: Replete Potassium to 4.5–5.0 mEq/L and accelerate heart rate to 90–110 bpm [3,4].

1. Brugada Electrical Storm: Isoproterenol 1–5 mcg/min IV infusion (15–75 mL/hr of 4 mcg/mL bag) + Quinidine 300–600 mg PO q6h + Acetaminophen 1,000 mg IV + active cooling [3].
2. Refractory Pause-Dependent TdP: Isoproterenol 2–10 mcg/min IV or Transvenous Overdrive Pacing at 100–110 bpm (strictly in pause-dependent LQTS) [3,4].

In Brugada, β-agonism (Isoproterenol) boosts inward Ca,L and Quinidine blocks outward to, restoring the right ventricular epicardial action potential dome [3]. In acquired TdP, accelerating HR shortens the QT interval and prevents long-short R-R pauses [3,4].