Thrombotic Complications

Unfortunately, thrombotic complications after IVC filter placement have not been studied thoroughly. The only prospective, randomized trial of IVC filter outcomes was performed by the PREPIC study group. Four hundred patients with proximal DVT at risk for PE were randomized to receive an IVC filter followed by anticoagulation or to

TABLE 47.2 Two-Year and Eight-Year Results of the PREPIC Trial of IVC Filter Use to Prevent Pulmonary Embolism15,16

anticoagulation alone (either unfractionated heparin or low-molecular weight heparin followed by vitamin K antagonists). Two reports addressing recurrent DVT, pulmonary embolism, IVC thrombosis, and post-thrombotic changes were published.15,16 There was no significant difference in the duration of anticoagulation between the two groups.16 At both two and eight years of follow-up there was a significantly increased risk of recurrent DVT in patients with an IVC filter compared to patients without filters (see Table 47.2). At two years there was no difference in the rate of symptomatic pulmonary embolism between the groups; however, by eight years of follow-up there was a 63% decrease in the risk of recurrent PE in patients receiving an IVC filter compared to patients without (see Table 47.2).15,16

Deep Venous Thrombosis

Recurrent deep venous thrombosis after IVC filter placement may include propagation of an existing thrombus into additional venous segments, involvement of a new venous segment including the contralateral limb, or insertion site thrombosis. A comprehensive review of IVC filters by Streiff in 2000 compiled the reported complications from available filters including the stainless steel Greenfield (SSG), titanium Greenfield (TG), Bird's Nest (BN), Simon Nitinol (SN), and VenaTech (VT).9 Most included studies were either retrospective reviews or prospective follow-up performed by chart review, questionnaires, or clinic visits as opposed to serial radiographic surveillance. In Streiff's review the SSG and the BN filters had the lowest rates of recurrent deep venous thrombosis, 5.9% and 6%, respectively.9 The highest rates of DVT have been seen with the TG (22.7%), the VT (32%), and the TrapEase (45.7%).9,10 However, these results were generated from small studies with very few enrolled patients.

Since there are no prospective comparative studies of IVC filters, it is difficult to determine whether the risk of recurrent venous thrombosis relates to the presence of a filter or if specific design issues are related to thrombogenesis. The PREPIC trial, which used the VenaTech and the Titanium Greenfield filters in 56% and 26.5% of patients, respectively, documented increased risk of recurrent symp tomatic DVT in patients with filters compared to patients without a filter.15 Although is unlikely that comparative studies of specific devices will be performed, further study of filter design and thrombosis may help clarify factors contributing to thrombosis.

Deep venous thrombosis at the insertion site has been documented following IVC filter placement. With routine surveillance, insertion site thrombosis has been identified in 14 to 64% of patients. Since IVC filters may be inserted by femoral, jugular, or brachial routes, insertion site thrombosis may occur in an unprotected venous bed.9 The newer low-profile delivery systems being developed may decrease the risk for insertion site thrombosis. To document the actual frequency of this complication, however, studies will need to incorporate routine surveillance of the insertion site into protocols.

Post-Thrombotic Syndrome

After a DVT, clinical symptoms of the post-thrombotic syndrome increase over time. At eight years follow-up, post-thrombotic symptoms are observed in approximately 70% of patients with or without IVC filter placement.15 Given the high rate of post-thrombotic complications in patients with VTE, recurrent symptoms of discomfort, erythema, edema, and increased warmth are not uncommon. If recurrent deep venous thrombosis is suspected, patients should undergo further evaluation. Imaging with venous duplex ultrasound or venogram may be used to determine whether the patient has had proximal or distal propagation of existing thrombus or recurrent DVT in a new venous segment. In some cases determining the age or chronicity of the thrombus is difficult. In this setting D-dimer measurement may assist in making this determination. Compression stockings are recommended following a DVT with or without IVC filter placement to decrease the risk of post-thrombotic syndrome symptoms.

Pulmonary Embolism

IVC filter placement is one method of managing DVT and preventing PE in patients unable to be anticoagulated. However, despite IVC interruption, pulmonary embolism may occur. The origin of pulmonary emboli in this setting includes propagation of thrombus proximal to the IVC filter (see Figure 47.1), small emboli that pass through the filter, emboli from unprotected venous beds including the upper extremity, or embolism through developed pelvic or abdominal veins or collaterals such as the azygous or ovarian vein. Cumulative rates of recurrent symptomatic PE in the PREPIC trial were 1.1%, 3.4%, and 6.2% at 12 days, two years, and eight years follow-up, respectively. Two patients (1%) suffered fatal PE.15,16 From the reviews by Streiff and Kinney, 40 studies of the SSG filter demonstrated a

Recurrent DVT" Symptomatic PEb

TABLE 47.2 Two-Year and Eight-Year Results of the PREPIC Trial of IVC Filter Use to Prevent Pulmonary Embolism15,16

Recurrent DVT" Symptomatic PEb

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