[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 (D _a ) and in superior-inferior direction (D _b ). Using a formula for converting circumference to diameter, the equivalent circle dimensions were calculated (D _e , D _e =minor axis+2 (major axis-minor axis)/3). Taking the data of 75% RRI phase, the patients were divided into D _a75%RRI ≥D _b75%RRI group and D _a75%RRI <D _b75%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-POD _laoc ) was calculated with the correction formula. Scatter plots of the changes of the mean values of D _a , D _b and D _e with the cardiac cycle were presented. The change and ratio of measured values of D _a and D _e at 35% and 75% RRI was calculated. The ratio of D _e change to D _a change in D _a75%RRI ≥D _b75%RRI group and D _a75%RRI <D _b75%RR group was calculated, respectively, and compared between groups. Pearson correlation analysis was used to explore the correlation between CR-POD _lao c and D _e35%RRI and D _e75%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 D _a75%RRI ≥D _b75%RRI and 27 cases into group D _a75%RRI <D _b75%RRI . Both D _a and D _b regularly changed at each phase throughout the cardiac cycle. The D _a 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 D _b 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 D _a was (6.35±2.46) mm, and the ratio of D _a values at 35% and 75% RRI was 0.77±0.08. The change of D _e was (2.28±1.32) mm, and the ratio of D _e at 35% and 75% RRI was 0.93±0.05. The ratio of D _e change to D _a change in the D _a75%RRI ≥D _b75%RRI group was 0.67±0.13; while the ratio was 0.34±0.05 in D _a75%RRI <D _b75%RR group, and there was significant difference between the two groups ( P =0.02). CR-POD _lao c was positively correlated with D _{e35% RRI} ( r =0.99, P <0.001) and D _{e75% RRI} ( r =0.98, P <0.001). Conclusions: Most secundum ASDs show oval shape with D _b >D _a . D _b is basically constant while D _a 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 D _e at 35% RRI phase, which is helpful for the successful intervention.