Background  Tetralogy of Fallot (TOF) is one of the common complex congenital heart diseases. Although mixed reality technology has been widely used in many medical fields, few researches have been reported in the perioperative evaluation of the heart disease.

  Objective  To explore the value of mixed reality technology in the preoperative evaluation of TOF and provide evidences for clinical application.

  Methods  Consecutive cases admitted to the First Medical Center, Chinese PLA General Hospital from August 2018 to August 2019 with a diagnosis of TOF by echocardiography were enrolled. The three dimensional cardiac model was reconstructed after preoperative cardiac CT angiography, and the location, shape and size of the ventricular septal defect (VSD) were obtained using a Hololens (Microsoft, USA) mixed reality device. The sizes of VSD measured by mixed reality three-dimensional (3D) model, echocardiography, and actually measured intraoperatively were compared.

  Results  A total of 32 patients were enrolled in the study. The diameters of VSD measured by echocardiography, mixed reality 3D model, and actual VSD were (13.44±3.25) mm, (17.19±2.29 mm, and (18.75±3.82) mm, with significant differences between the groups (P＜0.001). However, there were no differences in short diameters (14.69±2.02 mm vs 14.31±3.11 mm, P=0.788) and estimated area (203±54 mm² vs 217±80 mm², P=0.691) between mixed reality 3D model and actual VSD. The average time to reconstruct a single mixed reality image was 38.6 minutes.

  Conclusion  Mixed reality technology can provide accurate location, shape and size of VSD in TOF, which can help surgeons better understand the internal and external structures of the heart, thus providing a new approach to the preoperative evaluation of TOF.