IVC filter devices aim to prevent pulmonary thromboembolism in patients with lower limb deep venous thrombosis. Literature demonstrates that many IVC filters that are placed may not be retrieved, thus increasing the likelihood of future complications. Ramakrishnan G, et al7 analysised that 1.8% and 3.1% developed immediate and delayed complications in 14,784 patients, and Thrombosis in filter was very common. A systematic review of retrievable IVC filters found that primary complication rates varied widely with thrombosis ranging from 6–30%8. Therefore, it brought with many challenges for retrieving filters. In terms of treatment for filter thrombosis, CDT could reduce thrombus burden in filter for those with acute or subacute thrombus9, but even someone had the high risk of bleeding and the thrombosis had not removed completely. Such as in our study, 4 patients had not assisted with CDT because of the high risk of bleeding, including 1 person along with abdominal hematoma, and the feature of thrombus tends to be chronic in other 3 persons. Comparing with CDT alone, Li WD, et al.10 found that CDT combined with aspiration thrombectomy had better performing thanks to a shorter thrombolysis time and a lower urokinase dose required. However, increasing the occurrence of complications, such as acute renal injury and hemoglobinuria. Therefore, it was still necessary to find an effective solution to avoid these risks for patients with IVC filters-mediated thrombosis.
In our study, we used suprarenal IVC filter to protect the patient and retrieval double filters successfully accompanied by thrombosis which was found no more than two weeks. The result of this method was satisfactory. Nevertheless, the indications and procedures with using double filters should been grasped.
First, how to place and remove the second filter is important. As for the suprarenal IVC filter, seeking a suitable situation for placement would be very important. Before placed the suprarenal IVC filter, we should comprehensively evaluate on imaging of IVC and clarify the situation between the filter and thrombosis. Traditionally, the suprarenal IVC filter placement is preferred by femoral vein access. However, if a free-floating thrombus above the infrarenal filter, jugular vein access is suitable. Sometime, the diameter of the IVC is related to venous return, blood volume, and the respiratory cycle. Compared with an infrarenal IVC, a suprarenal IVC is larger in diameter but shorter in length11. When the suprarenal IVC is too larger to deployed the filter, we will choosing in those position but not released completely in order to remove it convenient with the I stage. As for the time to remove the suprarenal IVC filter. In our study, 6 of 7 patients had retrieved at the I stage, only 1 person still had partial thrombosis in suprarenal IVC filter after removing the first filter through venography, 2 weeks later with adequate anticoagulation therapy, she was scheduled to imaging again and showed that the thrombus was significantly reduced, and then, the suprarenal IVC filter was removed out. In our study, the renal vein thrombosis had not encountered in those process. We thought the reasons of that the anticoagulant therapy was followed after placement of the suprarenal IVC filter. Besides, it was more attention to reduce the thrombus escaped into the renal vein. Especially for those thrombosis under the filter.
Second, the risk of bleeding for thrombolysis treatment should been evaluated. Especially, for the elderly patients or someone who has low hemochrome and combined with more underlying diseases. During the treatment of CDT, we suggest that the thrombolytic catheter should be inserted across the thrombus. Certainly, clotting function should be closely monitored to evaluate the risk of bleeding. As for whether to thrombolysis treatment or not, it depends on the sign of inferior vena cava angiography. For example, fresh thrombus is usually attached to the vascular wall and will not sway with the breath, however, the old thrombus was mostly located in the middle of the filter.
Additionally, it is a critical step on how to removal the thrombus maximize. We exchanged 9F guiding catheter to retrieve the filter and part thrombus adhered on the filter. In this process, the most important thing was keeping a negative pressure of 20 mL syringe to collect the residual thrombus remaining in the 9F catheter. If the suction was not smooth, the guide wire was reserved, and the 9F catheter was washed in vitro and reinserted again. And then, the IVC angiography was been done again to assess whether to remove the suprarenal IVC filter or not. For clear away of the thrombolysis in filter, some scholars12 have tried with long sheathed thrombectomy, but in fact, it is disadvantage for losing more blood during the process. For further to assess the value and safety of this technique requires additional studies in the future.
Furthermore, while the filters retrieval, it should be more attention to observe the patient's blood oxygen saturation and whether there was a transient chest shortness of breath and other symptoms or not. If the patients had those symptoms, venography of pulmonary artery should be taken action as soon as possible, and confirmed the degree of pulmonary embolism or not. Sometimes, thrombus fragmentation by pigtail catheter would helpful with the thrombus filled on the trunk of pulmonary artery. In our study, we not come across this circumstance.
Certainly, the present study has several limitations. First, the number of patients are small, further study and observation of large samples are still needed in the later period. In addition, there has many different filter types been used in IVC, so the generalizability of this study may be limited.