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IVUS-Guided Vena Cava Filter Placement: Technique and Clinical Decision Algorithm
Although contrast venography is the standard imaging method for vena cava filter insertion, intravascular ultrasound (IVUS) is a safe and effective alternative that allows for bedside placement options, and is especially advantageous for critically ill patients.1–9 Depending on the clinical situation and the filter type used, either a single- or dual-puncture technique can be used. Feasibility of one technique over the other depends on understanding filter design and delivery catheter features. The following will describe the essential steps for IVUS-guided vena cava filter placement including preprocedural imaging, single access and dual-access techniques. A proposed clinical decision algorithm for IVUS-guided vena cava placement established according to evidence-based guidelines will be reviewed.
IVUS System and Filter Choice
Although smaller-profile IVUS probes can be used, the image size produced with the increased megahertz (MHz) probe is usually too large for adequate visualization of adjacent anatomic landmarks. Depending on the IVUS system used, usually an 8 Fr or greater sheath will be needed for IVUS imaging. For the Volcano s5™ or s5i™ system (Volcano Corp., San Diego, California), the company’s Visions® PV8.2F (8 Fr/8.3 MHz) IVUS probe is preferred over its Eagle Eye® Gold (5 Fr/20 MHz); for Boston Scientific systems (Boston Scientific Corp., Natick, Massachusetts), the cart version of the iLab® Ultrasound System with Sonicath® Ultra-9™ (9 Fr/9 MHz) or the Atlantis® PV Peripheral Imaging Catheter (8 Fr/15 MHz) are preferred for imaging the entire vena cava and surrounding landmarks. Because of IVUS probe size requirements, the single-puncture technique is limited to those filter delivery systems that use an access sheath size large enough to allow passage of the IVUS probe (≥ 8 Fr), while the dual-puncture technique can be performed with any of the currently U.S. Food and Drug Administration (FDA)-approved permanent and optional filter designs independent of filter delivery catheter size (Table 1).
Pre-Procedure Imaging
Prior to filter placement, venous ultrasound is obtained to evaluate the patency of the intended femoral access site(s) and to measure vena caval diameter. In most critically ill patients, especially the trauma population, a computed tomographic (CT) scan of the abdomen is usually available and should also be reviewed to determine vena caval anatomy, especially the position and location of the renal veins and iliac vein confluence, and to confirm the presence or absence of any venous anomalies. For IVUS imaging, following adequate local anesthesia, percutaneous femoral venous access is obtained. The IVUS probe is inserted into the sheath over the guidewire and directed into the inferior vena cava to the level of the right atrium of the heart. Using a pull-back technique, the venous anatomic landmarks are sequentially identified, including the right atrium, hepatic veins, renal veins and confluence of the iliac veins (Figure 1). If the location of the iliac vein confluence is unclear, additional contralateral femoral venous access is obtained for passage of a second guidewire, allowing precise identification of the iliac confluence at the level where this second contralateral wire is visualized in the inferior vena cava. The IVUS probe is directed just below the level of the lowest-most renal vein and inferior vena caval diameter measurements are made prior to proceeding with IVC filter deployment.
Single-Puncture Technique
A single venous access technique can be used if the filter delivery kit sheath exceeds 8 Fr. Sheath exchange is performed over the guidewire and the sheath is advanced to the predetermined level of the renal veins. The IVUS probe is used to precisely direct the end of the sheath to the level of the lowest-most renal vein. In this regard, IVUS is guiding sheath positioning, which, because of the measured length of the different filter delivery systems, indirectly guides the intended filter position. For filter systems with predetermined marks (such as Günther Tulip and Celect filters; Cook Medical, Bloomington, Indiana), the filter delivery catheter is advanced to the mark, aligning the tip of the filter with the end of the sheath, and then the sheath is withdrawn in a “pin-pull” fashion to allow deployment of the filter at the infrarenal level.10 For filter systems without predetermined marks (such as the Greenfield filter), the sheath is first pulled back over the intravascular probe for a distance equivalent to the length that the filter delivery catheter extends beyond the sheath (for the Greenfield filter, this distance is approximately 7 cm), so when the filter delivery catheter is loaded into the sheath, the tip of the filter will precisely align with the lowest-most renal vein upon deployment.11,12
Dual-Puncture Technique
If filter placement is not feasible with the single-puncture technique, and/or for lower-profile filter systems (Post-procedure Imaging The IVUS probe can be carefully advanced to confirm apposition of the filter legs to the inferior vena caval wall, but care should be taken in advancing the IVUS tip to avoid filter dislodgement (Figure 3). Post-procedure plain abdominal radiographs are obtained to verify filter position and alignment.
Clinical Decision Algorithm — IVUS Filter Placement
A clinical decision algorithm for IVUS-guided filter placement following current evidence-based guidelines is proposed (Figure 4)./sup>13–18 Indications for placement include standard indications (documented DVT or pulmonary embolism [PE] with contraindication or complication of anticoagulation), and prophylactic indications (high risk for venous thromboembolism [VTE] and an increased bleeding risk precluding anticoagulation-based prophylaxis). Choice of filter type is based on predetermination of permanent or optional needs using the following criteria: a permanent filter should be used when the anticipated risk of VTE extends beyond an acceptable retrieval window based on injury type or severity; an optional filter should be used if there is a defined retrievable endpoint within 6 months. Patients with retrievable filters are evaluated for removal 6 months after placement and the decision to proceed with removal is based on current medical status applied to accepted indications for retrieval.19 Preprocedural lower extremity venous duplex ultrasound is performed to evaluate the presence of lower-extremity DVT. If available, any preexisting CT scans are reviewed for vena caval and renal vein anatomic detail, thrombosis or anomalies. The decision to place the filter at the bedside is based on critical illness in the intensive care unit setting, injury type and severity and the potential risk of transportation. Placement of the filter in the endovascular suite is reserved for the following: non-critically ill patients when the transportation risk is low; if femoral access is not possible (bilateral lower extremity DVT); in the presence of IVC thrombosis; and/or vena caval anomalies that would preclude safe placement. Additional venographic guidance is also required for failure of bedside techniques due to inadequate imaging or access, or if a bedside-placed filter is malpositioned. In our published experience,20 successful placement of IVC filters using IVUS at the bedside in critically ill patients was established via this prospectively implemented evidence-based algorithm. In this series, 109 patients met criteria for IVUS-directed IVC filter placement. Technical feasibility was 98.1%. Only 2 patients had inadequate IVUS visualization for bedside filter placement and required subsequent placement in the endovascular suite. Of the remaining 107 patients, technical success defined as proper deployment in an infrarenal position was 97.2% (104/107). A permanent filter was used in 21 patients (19.6%), and a retrievable filter in 86 (80.3%). A single-puncture technique was utilized in 101 patients (94.4%), with additional dual access required in 6 (5.6%). Periprocedural complications were rare, but included malpositioning requiring retrieval and repositioning (n = 3), filter tilt ≥ 15º (n = 2) and arteriovenous fistula (n = 1). Thirty-day mortality for the bedside group was 5.5%, with no filter-related deaths.
Discussion
Technical feasibility of IVUS-guided filter placement based on adequate imaging is high, approaching 98–100%, while the potential for malpositioned filters is low, approximately 1–3% in most series. Malpositioned filters can be managed with percutaneous retrieval and repositioning techniques when optional filter designs are used, and even for some of the permanent filter designs, allowing for an effective rescue technique without significant additional morbidity or mortality.21 Understanding filter device component relationships in order to achieve technical accuracy for filter delivery using IVUS is critical. As bedside IVUS filter techniques continue to evolve, the single and dual techniques described above highlight the feasibility and safety of filter placement using IVUS. Although contrast venography remains the “gold standard,” bedside IVUS filter techniques offer some advantages when implemented through a decision algorithm, especially in the immobilized or critically ill patient in whom transportation may carry some risk, and must be weighed against the advantages of venography.
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From the Section of Vascular Surgery and Endovascular Therapy, University of Alabama at Birmingham, Birmingham, Alabama. The author reports no conflicts of interest regarding the content herein. Address for correspondence: Marc A. Passman, MD, Associate Professor Surgery, University of Alabama at Birmingham, Section of Vascular Surgery and Endovascular Therapy, BDB 503 1808, 7th Avenue South, Birmingham, AL 35294-0012. E-mail: Marc.Passman@ccc.uab.edu
