Thrombus formation after the Norwood procedure: Incidence, risk factors, and its impact on late outcomes.

Objective: Thrombus formation is a feared complication after congenital heart surgery. We aimed to clarify the clinical characteristics associated with thrombus formation after the Norwood procedure. Methods: All neonates who underwent the Norwood procedure between 2001 and 2022 were reviewed. The incidence and location of thrombus were evaluated. Risk factors for thrombus formation and its impact on survival were analyzed. Results: Among 360 patients who were included, thrombus formation was detected in 42 patients (11.7 %) during the postoperative in-hospital period, with a median of 12 (range: 5-30) postoperative days. The most common site of thrombus was the superior vena cava in 9 (2.5 %) patients, followed by the right atrium in 8 (2.2 %). Patients who received a right ventricle to pulmonary artery conduit had a higher incidence of thrombus than those who received a modified Blalock-Taussig-Thomas shunt (16.4 vs. 7.7 %, p = 0.011). Patients with thrombus formation had a longer stay in the intensive care unit (ICU), than those without (median 21 vs. 13 days, p = 0.018). Survival after ICU discharge was lower in patients with thrombus than those without (57, 54, and 54 % vs 73, 71, and 70 % at 2, 4, and 6 years, respectively; p = 0.032). Restrictive atrial septal defect was identified as an independent risk for thrombus (odds ratio: 2.61; p = 0.005). Conclusions: Thrombus formation was observed in 12 % of the patients during the hospital stay after the Norwood procedure and was associated with prolonged recovery and high mortality. A restrictive atrial septal defect was identified as a risk factor for thrombus formation.