A male infant was diagnosed at 42 days with complex congenital heart disease, including double outlet right ventricle, large ventricular septal defect, atrial septal defect, and pulmonary stenosis. At 6 months, he underwent a bidirectional Glenn procedure with main pulmonary artery ligation, improving SpO₂ from 85 % to 90 %. Six months later, progressive cyanosis and poor growth developed. At age five, he showed severe cyanosis, digital clubbing, and SpO₂ of 58–69 %.

Laboratory testing showed hemoglobin 225 g/L and hematocrit 73.3%. Arterial blood gas revealed PO₂ 30.7 mmHg and SO₂ 58.1%. Chest X-ray showed cardiomegaly (cardiothoracic ratio 0.6) and increased pulmonary markings. Echocardiography demonstrated a patent Glenn anastomosis. Contrast-enhanced CT revealed absence of the main pulmonary artery and diffuse pulmonary arteriovenous malformations (PAVMs) in both lungs, most prominent in the lower lobes.

Cardiac catheterization confirmed absence of antegrade pulmonary flow with well-developed bilateral pulmonary arteries. Distal pulmonary arteries and pulmonary venous branches were markedly dilated, some showing a granular or “string-of-beads” appearance. Pulmonary circulation time was shortened, indicating significant right-to-left intrapulmonary shunting consistent with diffuse PAVMs. Pulmonary artery pressure was 17/9/13 mmHg.

The operation was performed via a median sternotomy. Intraoperative exploration revealed that the ventricular septal defect was located in the inflow tract, distant from the aortic valve, making intracardiac tunnel construction infeasible; therefore, biventricular repair was not feasible. Under general anesthesia with hypothermic cardiopulmonary bypass, a total cavopulmonary connection (TCPC) was performed. The inferior vena cava was transected, and an 18-mm Gore-Tex conduit was anastomosed end-to-side to the right pulmonary artery, establishing a complete cavopulmonary circuit. Immediate postoperative oxygen saturation was approximately 75%. The total operative time was 6 hours and 14 minutes, with an aortic cross-clamp time of 50 minutes. The patient remained in the intensive care unit for 8 days and was discharged on postoperative day 19 after an uneventful recovery and stable hemodynamics. During a 2-year follow-up, peripheral oxygen saturation gradually increased and stabilized at 97–100%, with markedly improved exercise tolerance, resolution of digital clubbing, and normal skin color. Repeat cardiac catheterization confirmed unobstructed conduit flow and well-developed pulmonary vasculature. The previously extensive bilateral pulmonary arteriovenous malformations had completely resolved, pulmonary circulation time normalized, and pulmonary artery pressures measured 13/11/12 mmHg.

Diffuse PAVMs are a rare but serious complication after the Glenn procedure. This case shows that the loss of hepatic venous return contributes to their development, while restoring hepatic flow to the pulmonary circulation through TCPC can reverse PAVMs and normalize oxygenation. Cardiac catheterization plays a pivotal role in diagnosis, hemodynamic evaluation, and management planning. Early interventional assessment and timely completion of TCPC are crucial to improving outcomes in patients with unexplained hypoxemia after Glenn palliation.