Background and Aims: Vena cava filter implantation is the most direct and effective approach to prevent the occurrence of pulmonary embolism in patients with deep vein thrombosis of the lower limbs, and has been widely used in clinical practice. The convertible vena cava filter has more flexible time limits and simpler conversion operation in using for prevention of pulmonary embolism. However, the data of its clinical application are still limited. Therefore, this study was conducted to comprehensively assess the clinical application characteristics of convertible vena cava filters through a single-center retrospective analysis. 
Methods: The clinical data of 52 patients undergoing convertible vena cava filter implantation under DSA guidance in our center were retrospectively analyzed. The parameters for each individual case were measured to identify the safe distance of placement, which included the diameter of inferior vena cava, the distance between the bifurcation of the iliac veins and the opening of the low-side renal vein, the length of forward motion during release, and the length and width of the filter after release. In addition, the conversion time and intra-operative situation during filter conversion were collected, and the conversion skills in complicated cases were discussed.
Results: After measurement, the mean distance between the bifurcation of the iliac veins and the opening of the low-side renal vein was (116.4±13.2) mm, which was far much longer than (54.6±1.3) mm of the mean length of filter after release. The mean width of filter after release was (22.9±3.0) mm, which was slightly greater than (20.8±3.4) mm of the mean diameter of the inferior vena cava. Forward motion during release occurred in 19 patients (36.5%), and the mean length of forward motion was (6.5±1.8) mm. There was no filter tilt occurred in all cases after release. In the 48 patients planned to perform filter conversion, filter was successfully unlocked in one session in 42 cases (87.5%) with anaverage time of (4.5±0.8) min, of whom, 39 cases (81.3%) with unopened or in completely opened after removal of the retrieval hook, the filters were completely opened by the assistance of pigtail catheter stirring. In the 41 patients undergoing overdue conversion (>2 months), filter conversion was finished in 37 cases (90.2%) in one attempt, of whom, 4 cases (8.5%) underwent the conversion by assistance of gooseneck snare catheter combined with guidewire looping technique, because of the vessel wall attachment of the retrieval hook.
Conclusion: Convertible vena cava filter is a safe and easy-conversion filter option. Forward motion phenomenon should be considered during filter release. In patients exceeding the time limit of conversion, the conversion rate in one session is still high.