IVCF has been widely used in the daily clinical practice, although some studies have demonstrated that the application of retrievable IVCF did not prevent VTE recurrence or mortality compared with anticoagulation alone [6, 13]. In our medical center, the proportion of patients undergoing thrombolysis therapy accounted for a sizable part of patients with IVCF placement. Concerns regarding the long-term outcomes of filters have resulted in the application of retrievable IVCF, especially in patients with a long life expectancy. Actually, there were always some reasons why the filter cannot be retrieved from patient who no longer requires transient protection against PE.
To date, whether it is necessary to perform concomitant anticoagulation following non-retrieved IVCF insertion remains controversial. There are some published studies that advocate the application of post-filter anticoagulation therapy which reduced the occurrence of filter-related thrombosis or recurrent VTE and should be performed whenever possible [14, 15]. Conversely, several other studies evaluated the benefits of concomitant anticoagulation and found no evidence suggesting that such therapy was necessary [16, 17]. The incidence of VTE following filter insertion with concomitant anticoagulation was not statistically different from that in subjects who did not receive anticoagulation. Generally, the decision whether or not to perform concomitant anticoagulation depended on the preference of surgeon. There are many potential advantages of concomitant anticoagulation following filter insertion. Firstly, it may prevent the progress of thrombosis. Secondly, it may decrease the occurrence of filter thrombosis following insertion. Thirdly, it may further decrease the risk of recurrent VTE, especially in patients presenting with a first episode of unprovoked VTE. However, the adverse events of long-term anticoagulation include well-known risks of complications, particularly bleeding complications, in patients receiving anticoagulation. Balancing the competing risks of thrombosis and bleeding can be a difficult choice in these patients. In our study, probably due to the concomitant anticoagulation, the incidence of filter thrombosis was lower than that reported in the published studies [7].
The commonly available oral anticoagulation drugs in patients undergoing filter insertion were vitamin K antagonists which inhibit the synthesis of vitamin K-dependent coagulation factors. However, whether or not the patients receiving adequate anticoagulation or the duration was not presented in most studies. Currently, insufficient evidence exists to establish a standardized warfarin anticoagulation protocol for the prevention of filter thrombosis and recurrent VTE after filter insertion. In our medical center, some patients still chose warfarin as long-term anticoagulant therapy option. Unfortunately, severe complications or patient compliance with regular INR testing leaded to the cessation of warfarin administration. As for rivaroxaban, the EINSTEIN-DVT study demonstrated that rivaroxaban was not inferior to warfarin in the treatment of VTE. However, the study was based on the general VTE population and patients with IVCF insertion were excluded. Whether or not rivaroxaban is effective anticoagulant option for filter thrombosis is uncertain. In our study, the extended anticoagulant therapy was rivaroxaban 10 mg daily and the results showed that rivaroxaban did not reduce the incidence of filter thrombosis, but it could significantly reduce the incidence of bleeding events. This may be due to the fact that patients taking warfarin were unable to regularly monitor blood coagulation for long time. Unlike warfarin, rivaroxaban has clinical advantages of fixed dosage, require no coagulation monitoring and fewer drug-drug interaction. Considering the necessity of long-term anticoagulation for patients with non-retrieved IVCF, rivaroxaban should be a reasonable and valuable option.
According to our study, the observed difference in thrombosis incidence may be attributed to inherent filter design differences. Most symptomatic filter thrombosis occurred in the patients with TrapEase, OptEase or Aegisy IVC filters, which had the opposed biconical design. The structural style has been reported to have a higher incidence of filter thrombosis [18, 19]. Based on a vitro study investigating the hemodynamic effects of thrombosis entrapment by the TrapEase filter [20], the opposed biconical design made the thrombosis to be trapped between the filter and the vessel wall in the inferior region. The margination effect would generate a large region of flow stagnation that is considered to be the potential mechanism of flow-induced filter thrombosis. Alternatively, the design was intended to capture migrating thrombosis more effectively and limit the migration of filter. This margination effect did not appear in the single-cone design of the Greenfield, Günther Tulip and G2 filters [21, 22], which trapped the thrombosis to a central location where the blood flow was relatively high.
Moreover, two patients in each group with filter thrombosis were diagnosed with cancer, including lung adenocarcinoma, gastric cancer, ovarian cancer and pelvic cancer. It is well known that the hypercoagulable state has been recognized in patients with cancer. Patients with active cancer or those undergoing active treatment frequently experience thrombosis events [23]. Rivaroxaban 10 mg daily may indicate insufficient anticoagulant intensity for the prevention of filter thrombosis in those patients. These appears to be a need for further research to determine the optimal dose of extended thrombosis prophylaxis. Due to the high risks for VTE recurrence, patients with cancer might often be considered for IVCF placement in the real world. Therefore, the optimal long-term anticoagulation of these patients should be enough to arouse our attention.
This study also has several limitations. Firstly, the study was a retrospective cohort study, which can be influenced by the selection bias or unmeasured confounders. The filter placement and choice of filter type were determined by the physician. Secondly, although the time span was extended, the sample size in the study was insufficient because of few patients who need permanent IVCF insertion and low filter recovery failure rate in our urban medical center. Therefore, further and larger studies are needed to draw definite conclusions.