Case Report: 26-year follow-up after total cavopulmonary connection in crisscross heart-longitudinal assessment of anastomotic patency, biomarkers, and arrhythmia progression.

Crisscross heart (CCH) is an extremely rare congenital cardiac malformation, and literature on long-term outcomes after total cavopulmonary connection (TCPC) in CCH patients remains limited. We report a unique case demonstrating sustained anastomotic patency and objective postoperative evolution 26 years after TCPC in a patient with CCH. A 39-year-old female with crisscross heart and double-outlet right ventricle underwent TCPC at age 13 in 2000. Serial Doppler echocardiography (2013-2026) consistently demonstrated patent superior vena cava-right pulmonary artery anastomosis and inferior vena cava conduit without obstructive flow velocities (SVC-RPA: 30.6-43.9 cm/s; IVC conduit: 39.0-23.2 cm/s). The clinical course was complicated by progressive atrial arrhythmias: first-degree atrioventricular block with atrial premature beats (2017), atrial fibrillation with incomplete right bundle branch block (2020), and atypical atrial flutter (2026). NT-proBNP increased from 124 pg/mL (2024) to 592.3 pg/mL (2026), with persistently elevated hemoglobin (164-171 g/L). Management included beta-blockers for rate control and clinical surveillance without anticoagulation. At 26 years post-TCPC, the patient maintained NYHA functional class II, with patent Fontan pathways and preserved left ventricular function (EF 60%, 2026), and no protein-losing enteropathy, plastic bronchitis, or thromboembolic events. This case demonstrates that durable anastomotic patency and preserved functional status are achievable, while highlighting the inevitability of progressive atrial arrhythmias necessitating lifelong surveillance.