July 2011

Laser Removal
Radiology Today
Vol. 12 No. 7 P. 28

Delivering laser energy through a catheter can help interventionalists remove embedded IVC filters.

In the classic science fiction film Fantastic Voyage, scientists from the Cold War era Combined Miniature Defense Force shrink a submarine, a medical team—including a young Raquel Welch—and a laser to 1 µm in size. The tiny team is then injected into the bloodstream of a Soviet bloc defector so they can use the tiny laser to treat an otherwise inaccessible blood clot in his brain.

Sometimes science fiction does not become science fact because, except for the opportunity to dress Welch in a white cat suit, delivering laser energy through a catheter seems a better option all the way around. To that end, interventional radiologists are investigating using an excimer laser sheath to ablate adhesions restricting the removal of inferior vena cava (IVC) filters.

Interventionalists place cagelike IVC filters to trap blood clots before travel though the heart and cause pulmonary embolism (PE) by lodging in the lungs. Some IVC filters are designed to be permanent; others are meant to temporary. These filters are placed in patients at risk of PE when anticoagulant drug therapy cannot be used or is ineffective, according to an August 9, 2010, initial communication from the FDA describing some adverse events with IVC filters.

The use of these filters has grown significantly, particularly since the advent of retrievable filters in 2003. A report by Smouse and Johar published in Endovascular Today in February 2010 estimated that 259,000 IVC filters of all types will be deployed in 2012.

While a short-term survival benefit has been demonstrated in patients receiving IVC filters, the long-term risks and benefits are not clear.1 The FDA initial communication suggests that embedded filters increase the risk of IVC occlusion, chronic deep venous thrombosis (DVT), postthrombotic syndrome, filter fracture with component migration, and caval perforation with pain and organ injury, but data from larger cohorts are not available. In addition to the direct filter complication risk, many patients with permanent filters receive lifelong anticoagulation therapy to reduce thrombotic risks related to prolonged filter implantation, according to the researchers. Anticoagulation therapy brings its own inherent bleeding risks.

Retrievable IVC filters can usually be removed by guiding a catheter from a patient’s neck or groin to the filter and then grabbing and retrieving the filter by removing the catheter. The physician uses fluoroscopy and/or Doppler ultrasound to visualize the catheter as he or she moves it toward the filter. But in about 15%2 of the cases where temporary IVC filters are used, physicians have difficulty retrieving filters, often because of adhesions that develop between the filters and the walls of the vena cava.

William Kuo, MD, an interventional radiologist at Stanford University Medical Center, and colleagues recently published results of a study using an excimer laser sheath technique to photoablate these adhesions and ease the removal of the IVC filters. The paper was published in the June issue of the Journal of Vascular and Interventional Radiology (JVIR).

The FDA communication mentioned 921 device adverse event reports involving IVC filters. Those events included cases of device migration, detachment of device components, perforation of the vena cava, DVT, and filter fracture. One of the FDA’s concerns was that the retrievable filters were being left in patients.

“In short, our interest in filter research has been coincident with rising filter use over the past decade,” Kuo said in a podcast on the JVIR website discussing the paper. “Indeed, we’ve seen more and more patients now who have developed filter complications, and these patients have been inspiring us to develop new ways to help relieve their morbidity by removing their filter and also to relieve their anxiety and reduce further risks associated with long-term filter implantation.”

Pursuing Filters
In the hopes of ultimately increasing the number of IVC filters that can be removed successfully, Kuo and colleagues set out to study the safety and effectiveness of controlled photothermal tissue ablation of adhesions in embedded filters—both permanent and retrievable filters—using an excimer laser sheath technique. Their initial JVIR report looked at 25 prospectively enrolled patients who were scheduled to have their IVC filters removed. Seven different filter models from four manufacturers were included in the study. The study population included 10 men and 15 women between the ages of 20 and 76 (mean age of 50). Prospective patients were evaluated and counseled before the procedure, including an extensive informed consent process describing the risks and benefits of undergoing alternative retrieval maneuvers, including laser tissue ablation vs. the risks and benefits of having a permanent filter.

Prior to retrieval attempts, researchers assessed acute or recurrent DVT in each patient using Doppler ultrasound, CT venography, or conventional venography. When necessary, interventionalists performed thrombolysis of acute IVC thrombus one day before attempting to retrieve the filter using overnight infusion of alteplase.

Doctors in the study performed the retrieval procedures using moderate sedation in all cases except one that required general anesthesia because of severe nerve pain from filter leg penetration that had been identified during a previous retrieval attempt. Moderate sedation helped the physicians monitor acute pain, which could be a warning sign of impending caval injury. Nineteen patients were accessed through the right internal jugular vein while four were accessed via a common femoral vein. Two cases used simultaneous right internal jugular vein and common femoral vein access.

Researchers obtained a cavogram before all procedures, and all 25 patients were given therapeutic anticoagulation medication before or during procedures using high-risk retrieval protocol to minimize thrombotic risk during the procedure, according to the JVIR report. All patients received therapeutic anticoagulation during the procedure.

After previous retrieval attempts using standard methods had failed, researchers selected specific alternative removal techniques individualized to each patient. In patients with tilted, tip-embedded filters, the physicians used a snare-over-guide wire loop technique or endobronchial forceps3,4 to capture the filter tip before attempts to retrieve the filter over a standard snare or using a wire-loop technique.4

If the cephalad region of the filter or the main filter legs could not be sheathed and collapsed by the physician using aggressive force, the filter was considered a refractory embedded filter. At that point, physicians turned to the laser sheath technique. The aggressive force was originally subjectively determined but was measured using a digital tension force gauge in the final 10 cases in the series.

A 14-F, 16-F, or 18-F vascular sheath was first inserted to accommodate a corresponding inner 12-F, 14-F, or 16-F laser sheath. The laser sheath was connected to a Spectranetics CVX-300 Excimer XeCl laser system, and the laser tip was calibrated to 60 mJ/mm2 per protocol. When the vascular sheath was in place, the physician inserted the laser sheath into the vascular sheath and used it to manually collapse as much of the filter as possible before using the laser energy.

When the physician encountered resistance to the laser sheath, the laser was activated to attempt a controlled photothermal ablation of the adhesions. In some cases, adjunctive blunt dissection maneuvers using a to-and-fro motion of the outer coaxial sheath were used in addition to the laser energy.5 The researchers also performed a postprocedure cavogram on all patients in the study.

Results, Follow-Up, and Limitations
The researchers reported that the laser-assisted retrieval procedure was successful in 24 of 25 (96%) patients. Successful removal produced symptom improvement in all nine patients with filter-related morbidity. Among 21 patients with no underlying thrombophilia, successful filter retrieval allowed complete discontinuation of anticoagulation therapies in 18 (86%) patients. The other three patients in the group were in the process of completing an anticoagulation regimen when the journal issue containing the study went to press.

Lifelong anticoagulation was continued in three patients, two because of underlying thrombophilia and one because of a permanently embedded filter that could not be retrieved. (A complete summary of the cases can be viewed in the full article online at www.jvir.org/article/S1051-0443(11)00671-3/fulltext.)

Kuo and colleagues noted several significant limitations of their study. First, the work represented a small number of cases, and larger studies are needed to verify the safety and efficacy shown in the study. Second, the skills and techniques developed to retrieve filters at the medical center in the study may not be easily replicated in all facilities. Still, both of these limitations could be minimized over time, and Kuo and colleagues believe further work using the excimer laser to help retrieve IVC filters is warranted.

“Laser-assisted retrieval has the potential not only to abolish further risks from filter implantation but also to provide definitive treatment for patients experiencing embedded filter complications,” they wrote. “Our preliminary data suggest that careful use of this technique can allow removal of various embedded filters, including permanent types, with implantation lengths ranging from [a few] months to greater than 18 years. For all of these reasons, laser-assisted filter retrieval has the potential to impact the filter management algorithm by giving many patients new hope for preventing and alleviating morbidity related to prolonged filter placement.”

The excimer laser sheath technique also sidesteps Medicare billing and coding issues; there is still no code modifier for “submarine miniaturization, complex.”

— A Radiology Today staff report

 

References
1. PREPIC Study Group. Eight-year follow-up of patients with permanent vena cava filters in the prevention of pulmonary embolism: The PREPIC (Prevention du Risque d’Embolie Pulmonaire par Interruption Cave) randomized study. Circulation. 2005;112(3):416-422.

2. Ray CE Jr, Mitchell E, Zipser S, Kao EY, Brown CF, Moneta GL. Outcomes with retrievable inferior vena cava filters: A multicenter study. J Vasc Interv Radiol. 2006;17(10):1595-1604.

3. Stavropoulos SW, Dixon RG, Burke CT, et al. Embedded inferior vena cava filter removal: Use of endobronchial forceps. J Vasc Interv Radiol. 2008;19(9):1297-1301.

4. Kuo WT, Bostaph AS, Loh CT, Frisoli JK, Kee ST. Retrieval of trapped Günther Tulip inferior vena cava filters: Snare-over-guide wire loop technique. J Vasc Interv Radiol. 2006;17(11 Pt 1):1845-1849.

5. Kuo WT, Tong RT, Hwang GL, et al. High-risk retrieval of adherent and chronically implanted IVC filters: Techniques for removal and management of thrombotic complications. J Vasc Interv Radiol. 2009;20(12):1548-1556.