Cath Lab Digest

Abstract

The role of anticoagulants in the treatment of venous thrombo-embolic disease is well established. The use of inferior vena cava filters as a second line treatment is increasing, most recently with the popularity of of retrievable filters. However, the indications and evidence for their safety and efficacy are not clear-cut. There are few absolute indications. The majority of evidence originates from single-center series studying a preferred few genres of filters. Generalizability and meta-analysis are difficult. Important questions remain to be answered, particularly regarding extended indications for insertion, the long-term safety of retrievable devices, and the relative efficacy and safety of different genres of devices. Thus, filter insertion should be a careful and considered process in a multi-disciplinary environment.

Introduction

Venous thromboembolism (VTE) and its sequelae are an important problem. VTE occurs at a rate of 1/1000 in the general population, rising to 1/100 in the high-risk subpopulations.¹ Without treatment, patients with VTE are at high risk of developing pulmonary embolism (PE), which can be fatal in as many as 25% of patients.² There are now multiple agents available for treating VTE, from unfractionated heparin to low-molecular-weight heparins and fondaparinux. However, oral vitamin K antagonists remain the mainstay of long-term treatment.³

There are a number of situations where such forms of anticoagulation are not sufficient or possible. Anticoagulation can fail with breakthrough PE while on “therapeutic” anticoagulation therapy quoted at 4%.⁴ Anticoagulation may also result in serious complications, and may need to be discontinued. It is associated with death in up to 5% of patients. Heparin-induced thrombocytopenia (HIT) can occur in up to 3% of patients, 25% of whom will develop new venous and some arterial thrombosis, including PE.5–7 When anticoagulation is contraindicated or otherwise ineffective, interruption of the inferior vena cava (IVC) with a filter device may need to be considered.

In the past, mechanical interruption of caval flow had been surgical. Around 80% of all VTE results from lower-limb thrombosis⁸ and ligation of the femoral veins to prevent clots from reaching the pulmonary arteries. This was first suggested by Hunter as far back as 1874. Later, ligation of the IVC was performed, which had a high operative mortality rate of up to 15%, with recurrence of PE in 6% of patiand chronic venous insufficiency in 33%.⁹

In the 1960s, newer methods of partially interrupting the IVC were developed to reduce the effects of venous stasis using suture application and caval clips. Operative mortality and recurrent PE were still similar to those of caval ligation, and the rate for limb edema was reduced, but IVC occlusion rates remained high.

Such problems inspired the development of the Mobin-Uddin umbrella, an endovascular device developed in 1967 to partially interrupt the flow in the IVC and to prevent PE. This was followed by the Greenfield filter in 1971, both of which still required a surgical venotomy. The first widely available, truly percutaneous device was launched in 1981 by Greenfield and quickly replaced all open surgical procedures.

Since then, there has been rapid evolution in technology with smaller devices and flexible delivery systems, allowing delivery from multiple venous access sites under fluoroscopic guidance. There is now also the option of cases being performed under ultrasound guidance in an intensive care setting.¹⁰ These devices, however, are not without their long-term risks; this has driven the development of retrievable IVC filters, providing an option for short-term caval interruption. Today in our institutions, the majority of filters used are temporary.¹¹

Such developments in technology have encouraged a shift in “indications” for filter placement with increasing trends to utilize prophylactic filter placement and retrievable IVC filters. This has resulted in an explosion of the number of IVC filters placed. In the United States, this has increased almost 25-fold, from an estimated 2,000 placed in 1979, to an estimated 49,000 placed in 1999.¹²

Indications

There are limited robust data on the precise and correct indications for filter placement. Thus far, there has only been one randomized, controlled trial, the Prevention du Risque d’Embolie Pulmonaire par Interruption Cave (PRECIP) study.⁴ The majority of the available data are from case series or retrospective case reports. Following a systematic review of comparable data, the Cochrane group concluded that no firm recommendations could be made for filter placement and data from the PRECIP study could not be extrapolated to general use. The Cochrane group supported the use of IVC filters only in patients in whom anticoagulation was not feasible or where there was breakthrough PE. No recommendations could be made for many of the other indications that are widely practiced.¹³

Similar guidelines have been produced independently by the American College of Chest Physicians (ACCP) who recommend IVC filter placement only in those patients with proven VTE and with (i) a contraindication for anticoagulation; (ii) a complication of anticoagulation treatment; or (iii) recurrent VTE, despite adequate anticoagulation (Table 1).