17. Inherited Channelopathies and Primary Electrical Diseases
Channelopathies in adults require systematic risk stratification for the prevention of sudden cardiac arrest in individuals with structurally normal hearts.
Figure 17.1: Type 1 Brugada Pattern: Coved-type ST-segment elevation >= 2 mm followed by an inverted T wave in right precordial leads V1-V2.
1. Classification of Major Channelopathies
| Channelopathy | Mutated Genes / Channels | Classical 12-Lead Electrocardiographic Hallmark | Provocative Testing & Diagnostic Triggers | Definitive Management |
|---|---|---|---|---|
| Brugada Syndrome (Type 1) | $SCN5A$ ($Nav1.5$, loss-of-function in $20-30\%$). | Coved-type ST elevation $\ge 2\text{ mm}$ followed by a negative T wave in $\ge 1$ right precordial lead ($V_1-V_2$ in 4th, 3rd, or 2nd intercostal space). | Fever, high carbohydrate meals, psychotropic drugs, Sodium Channel Blocker Challenge (IV Ajmaline $1\text{ mg/kg}$ or Flecainide $2\text{ mg/kg}$). | ICD Implantation; Quinidine ($300-600\text{ mg}$ tid); Epicardial RVOT Catheter Ablation. |
| Short QT Syndrome (SQTS) | $KCNH2, KCNQ1, KCNJ2$ (gain-of-function $K^+$). | Corrected $QTc < 330-360\text{ ms}$ with tall, narrow-based, peaked T waves; virtually absent ST segment. | Short atrial/ventricular refractory periods; easily inducible VF during EPS. | ICD Implantation; Quinidine (prolongs QT interval and normalizes repolarization). |
| Early Repolarization Syndrome (Malignant ERS) | $CACNA1C, KCNJ8, SCN5A$. | J-point elevation $\ge 1\text{ mm}$ with horizontal or downsloping ST segment in inferior (II, III, aVF) or lateral leads. | Hypothermia, bradycardia, high vagal tone. | ICD; Isoproterenol infusion for electrical storm; oral Quinidine. |
| Catecholaminergic Polymorphic VT (CPVT) | $RyR2$ (90%), $CASQ2$ (intracellular $Ca^{2+}$ leak). | Completely normal resting baseline ECG; Bidirectional VT or polymorphic VT provoked during exercise/stress. | Exercise Treadmill Test (ETT) or Isoproterenol infusion reproducing bidirectional VT. | Nadolol + Flecainide; Left Cardiac Sympathetic Denervation (LCSD); ICD with high-rate cutoff. |
2. Emergency Management of Brugada Electrical Storm
- IV Isoproterenol Infusion: Titrated to increase heart rate by $20\%$, increasing inward $I_{Ca,L}$ to overcome outward $I_{to}$ and aborting VF storm.
- Oral / IV Quinidine: Blocks $I_{to}$, normalizing ST-segment elevation.