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[Three-dimensional volume rendering for dynamic characteristics of secundum atrial septal defect during various phases of the cardiac cycle and the impact on occluder selection].

Objective: To investigate the dynamic change of the secundum atrial septal defect (ASD) throughout the cardiac cycle, and assess its impact on occluder selection. Methods: This study retrospectively analyzed 35 patients with ASD who received electrocardiogram-gated coronary CT angiography (CCTA) throughout the cardiac cycle as well as interventional closure therapy in Fuwai Hospital from December 2016 to December 2019. The raw data were reconstructed into 20 phasic images of RR intervals (RRI) ranging from 0 to 95% in an increment of 5% and transmitted to a workstation for postprocessing. For each phase image, CT virtual endoscopy reconstruction technique (CTVE) was used to provide views of ASD. Axial sequence assisted CT volumetric measurement (CTAS) was used to calculate the maximum dimensions in axial planes (Da) and in superior-inferior direction (Db). Using a formula for converting circumference to diameter, the equivalent circle dimensions were calculated (De, De=minor axis+2 (major axis-minor axis)/3). Taking the data of 75% RRI phase, the patients were divided into Da75%RRI≥Db75%RRI group and Da75%RRI<Db75%RR group. According to the postoperative chest X-ray, the waist diameter of the occluder in the left anterior oblique plain film was measured, and its correction value (CR-PODlaoc) was calculated with the correction formula. Scatter plots of the changes of the mean values of Da, Db and De with the cardiac cycle were presented. The change and ratio of measured values of Da and De at 35% and 75% RRI was calculated. The ratio of De change to Da change in Da75%RRI≥Db75%RRI group and Da75%RRI<Db75%RR group was calculated, respectively, and compared between groups. Pearson correlation analysis was used to explore the correlation between CR-PODlaoc and De35%RRI and De75%RRI. Results: A total of 35 patients, aged (42.7±15.0) years, including 10 males, were included. Among 35 patients, 8 cases were divided into group Da75%RRI≥Db75%RRI and 27 cases into group Da75%RRI<Db75%RRI. Both Da and Db regularly changed at each phase throughout the cardiac cycle. The Da changed significantly, with a maximum at phase of 35%-45% of RRI, and a minimum between phases of 90% and 0 of RRI. While the Db showed insignificant changes during phases of 10%-90% RRI, and increased at 0-10% of RRI, then reduced in the remaining phases. The change of Da was (6.35±2.46) mm, and the ratio of Da values at 35% and 75% RRI was 0.77±0.08. The change of De was (2.28±1.32) mm, and the ratio of De at 35% and 75% RRI was 0.93±0.05. The ratio of De change to Da change in the Da75%RRI≥Db75%RRI group was 0.67±0.13; while the ratio was 0.34±0.05 in Da75%RRI<Db75%RR group, and there was significant difference between the two groups (P=0.02). CR-PODlaoc was positively correlated with De35% RRI (r=0.99, P<0.001) and De75% RRI (r=0.98, P<0.001). Conclusions: Most secundum ASDs show oval shape with Db>Da. Db is basically constant while Da changes significantly during cardiac cycle (10%-90% RRI). Nonetheless, both values peak and maintain the maximum status at end-systolic phase (35%-45% RRI). For patients with huge ASD, occluder selection should be based on the De at 35% RRI phase, which is helpful for the successful intervention.