Single Ventricle / HLHS

Single ventricle physiology culminating in Fontan palliation creates a unique circulation characterized by chronic venous hypertension, absent subpulmonary ventricle, and profoundly altered hemodynamics . The Fontan circuit represents severe chronic right heart failure with sequelae including hepatic congestion, lymphatic dysfunction, restrictive lung disease, and progressive single ventricle dysfunction . Pulmonary vascular resistance in Fontan patients is typically both fixed and elevated, limiting cardiac output augmentation during exercise [e895-c5, e895-c12]. Diastolic dysfunction is nearly universal, with approximately 75% demonstrating abnormalities of early relaxation or elevated filling pressure on echo, and 35% showing occult diastolic dysfunction unmasked by volume challenge [e895-c14, e895-c19]. The circulation is profoundly prothrombotic—comparable to paroxysmal nocturnal hemoglobinuria—with cumulative thrombotic event risk reaching 22% and rising inexorably over time [e886-c5, e886-c6, e886-c7]. Arrhythmias, particularly macro-reentrant atrial tachycardia, were ubiquitous in early atriopulmonary Fontans and remain a significant predictor of adverse outcomes even in modern cohorts [e890-c1, e890-c14]. Fontan-associated liver disease progresses silently, with subclinical hepatocellular damage occurring when hepatic venous pressures exceed 25 mmHg . Protein-losing enteropathy and plastic bronchitis—manifestations of lymphatic pathology—carry 50% five-year freedom from death or transplant but resolve post-transplant in survivors [e891-c4, e891-c6, e891-c14, e891-c15]. Transplant outcomes have improved, with survival approaching 80% at one year and 75% at five years, though Fontan patients face higher waitlist mortality and early graft failure risk than dilated cardiomyopathy patients [e891-c8, e891-c11]. Mechanical support with continuous-flow VADs works well in appropriately selected patients ≥25 kg, offering bridge to transplant when medical management fails [e891-c19, e891-c21]. The key to optimizing long-term outcomes lies in dynamic assessment—exercise testing with hemodynamic monitoring reveals occult abnormalities invisible at rest—and aggressive management of modifiable risk factors including arrhythmia, thrombosis, and diastolic dysfunction [e894-c12, e894-c24].