Cardiac Resynchronization Therapy in Single-Ventricle Physiology: A Case Report of cc-TGA Managed With Fontan Strategy.

Cardiac resynchronization therapy (CRT) has been widely used in adult patients with heart failure and ventricular dyssynchrony, but its application in pediatric patients with congenital heart disease (CHD), particularly those with single-ventricle physiology, remains limited. We report the case of a male patient with congenitally corrected transposition of the great arteries (cc-TGA) and single-ventricle physiology who developed complete atrioventricular block and underwent single-chamber epicardial pacing at the age of four. A dual-chamber pacemaker was later implanted at the time of Glenn surgery. By age 12, in the pre-Fontan period, the patient showed signs of systemic ventricular dysfunction and electromechanical dyssynchrony, including a QRS duration of 167 ms, reduced left ventricular ejection fraction (35%-40%), and elevated NT-proBNP (1507 pg/mL). CRT upgrade was performed simultaneously with extracardiac Fontan completion. Postoperative improvement was significant, with QRS narrowing to 130 ms, normalization of ventricular function (EF: 50%), and NT-proBNP reduction to 146 pg/mL. This case illustrates the feasibility and potential benefits of CRT in patients with single-ventricle physiology, particularly when timed strategically with Fontan completion. It also supports emerging guideline recommendations for CRT use in systemic single-ventricle patients with symptomatic heart failure despite medical therapy.