There is much debate over certain aspects of the prevention and treatment of venous thromboembolism. However, most physicians agree that pulmonary embolism is a serious and potentially fatal condition, with approximately 300,000 patient deaths nationwide each year. Most of these deaths occur in hospitalized patients, and pulmonary embolism is considered the leading cause of preventable in-hospital mortality in the United States.
More than 12 million patients admitted to hospitals across the country are known to be at high risk of pulmonary embolism and need prophylaxis (Am. J. Hematol. 2007;82:777-82). The most recommended therapy, based on the American College of Chest Physicians guidelines, is the use of heparin or low-molecular-weight heparin as prophylactic anticoagulation (Chest 2008;133:454S-545S). An overwhelming number of patients receive this kind of therapy.
By Dr. Louis F. Angel
According to the guidelines, the use of filters is listed as an alternative for patients who are critically ill, are at high risk for pulmonary embolism, or have a contraindication to anticoagulation. These patients represent the minority of patients with VTE, but they are still in need of effective prophylactic therapy.
Anticoagulation has been shown to be a very safe therapy in most patients; however, for those patients who can’t have anticoagulation, inferior vena cava (IVC) filters are an effective alternative for preventing pulmonary embolism. The incidence of PE in patients who have vena cava filters in multiple clinical trials is about 1.3%, which is similar to the incidence reported in the PREPIC (Prevention of Recurrent Pulmonary Embolism by Vena Cava Interruption) study, a trial that randomized patients to anticoagulation plus a vena cava filter or to anticoagulation alone. In this study, the rates of PE during the first 12 days in patients with filters was 1.1%, and lower than in patients receiving anticoagulation alone (N. Engl. J. Med. 1998;338:409-16).
The research on IVC filters has not kept pace with the increasing clinical application of these devices. Why is there is no randomized, clinical trial studying the use of filters? In my opinion, it is because trials are extremely complicated to do in this population of patients. These are patients who have a high risk of venous thromboembolism, who already have a VTE or pulmonary embolism, and who can’t safely receive anticoagulation for many reasons, such as multiple trauma with bleeding, multiple operations, or intracerebral hemorrhage. These patients are at high risk for developing a PE and something must be done for them. If we can’t give anticoagulation, we can protect them with the use of IVC filters.
Only about 250,000 of the 12 million at-risk patients are receiving vena cava filters, and complications, even if considered severe, occur in fewer than 3% of the patients who receive filters as prophylaxis. The complications from vena cava filters are related to the period of time for which we use these devices, with few reported complications during the first 30 days of use. In some cases, the filters are used for a short period of time and are removed when the patient can go on anticoagulation therapy, or when he or she no longer has significant risk of VTE. In my opinion, the IVC filters are effective for preventing a pulmonary embolism and are safe for most of these high-risk patients.
In conclusion, the significant alarm about filter use is mostly related to the long-term complications and the lack of randomized studies evaluating their effectiveness. Although these devices are complicated, that is not to say that they are not useful in a selected group of patients, most of whom are in critical care or have contraindications to anticoagulation.
If we monitor these patients closely, follow them with prophylactic anticoagulation, and improve the rates of IVC filter retrieval, we can balance the risk-benefit profile of these devices, and they will continue to be considered a good alternative for high-risk patients.
Dr. Angel is the director of the lung transplantation program in the department of medicine and CT surgery at the University of Texas Health Science Center in San Antonio, and works with a company developing products for critically ill patients, including a vena cava filter.