23. Single Ventricle Physiology and the Palliative Surgical Pathway
Children born with single-ventricle anatomy (Hypoplastic Left Heart Syndrome, Tricuspid Atresia, Double Inlet Left Ventricle) undergo a staged three-tier surgical palliation culminating in the total cavopulmonary connection (Fontan circulation).
1. Staged Surgical Pathway & Electrocardiographic Evolution
STAGE 1: Norwood / Sano (Neonatal) -> Systemic RV / LV volume overload, wide QRS STAGE 2: Bidirectional Glenn (3-6 mo) -> Superior vena cava to pulmonary artery; partial unloading STAGE 3: Fontan Operation (2-4 yr) -> Total cavopulmonary connection; passive pulmonary flow
2. Post-Fontan Electrical & Arrhythmic Complications
- Intra-Atrial Reentrant Tachycardia (IART / Incisional Atrial Flutter):
- Rapid atrial rate ($200-300\text{ bpm}$) with macroreentry around suture lines or patch borders.
- In a Fontan patient with passive pulmonary blood flow, acute tachycardia causes catastrophic loss of cardiac output, acute hypotension, and plastic bronchitis / protein-losing enteropathy.
- Sinus Node Dysfunction: Common following extensive lateral tunnel or extracardiac conduit surgery.
3. Evidence-Based Clinical Management
- Acute IART Termination: Synchronized DC Cardioversion ($0.5-1.0\text{ J/kg}$) or transesophageal atrial pacing.
- 3D Electroanatomical Catheter Ablation: High-density voltage and activation mapping to identify isthmuses of slow conduction between surgical scars and anatomical boundaries.
- Epicardial Pacing: Dual-chamber epicardial pacing for severe sinus node dysfunction.