This study evaluated thrombus formation and its impact on outcomes in neonates and early infants undergoing congenital heart surgery.

Neonates and early infants (≤90 days) undergoing congenital heart surgery with cardiopulmonary bypass from 2001 to 2024 were analyzed. Thrombi were detected by transthoracic echocardiography and cardiac catheterization.

Among 2331 patients, 170 (7.3 %) developed thrombi during hospitalization. Median age at surgery and time to thrombus detection in affected patients were 12 (interquartile range: 7–34) and 7 (interquartile range: 3–15) days, respectively. Among surgical procedures performed in at least 10 patients, thrombi were most frequently observed following tricuspid valve repair (28.6 %), followed by arterial switch operation, ventricular septal defect closure, and aortic arch repair (15.8 %). The most common thrombus location was the superior vena cava in 61 patients, followed by the inferior vena cava in 33, the aorta in 31, and the right atrium in 21 patients. Additional surgical interventions were required in 28 patients. The length of hospital stay was significantly longer in patients with thrombi (27 vs. 15 days, p < 0.001). Independent risk factors for thrombus formation included preoperative cardiopulmonary resuscitation (odds ratio: 2.037, p = 0.001), tricuspid valve repair (odds ratio: 6.206, p < 0.001), and Norwood procedure (odds ratio: 1.558, p = 0.027).

The incidence of thrombus formation was 7.3 % in neonates and early infants undergoing congenital heart surgery. Thrombus was most frequently observed in the superior vena cava and resulted in prolonged hospitalization. Preoperative cardiopulmonary resuscitation, tricuspid valve repair, and Norwood procedures carried the highest thrombotic risk.