Vena cava filters

Nonpharmacologic methods improve venous blood flow by mechanical means and include early ambulation, electrical stimulation of calf muscles during prolonged surgery, graduated compression stockings, intermittent pneumatic compression devices, and inferior vena cava filters. 

The variety of medical applications for shape memory alloys is impressively hroad. These alloys are already used as stents inserted into blocked arteries, as vena-cava filters, as orthodontic devices, and in eyeglasses. 

SMAs are also used in another application related to cardiac health problems, as vena-cava filters. In some instances, it is desirable to protect a patient against the possibility that a blood clot formed elsewhere in the body will travel through the circulatory system into the heart, where it may cause a heart attack or stroke. Tiny, umbrella-shaped devices made of SMA materials have proven to he effective in such cases. In these devices, called vena-cava filters, the umbrella portion of the device consists of a mesh of tiny wires made of an SMA material. The device is inserted into the circulatory system in the form of a reduced-size (martensite phase), folded-up umbrella. Once in place, it is opened in such a way that the umbrella fills the vessel leading into the heart. The mesh design allows blood to flow through normally but filters out any blood clots that are carried along with the blood. 

Dewald CL, Jensen CC, Park YH, Hanks SE, Harrell DS, Peters GL, Katz MD. Vena cavography with CO(2) versus with iodinated contrast material for inferior vena cava filter placement a prospective evaluation. Radiology 2000 216(3) 752-7. 

White RH, Zhou H, Kim J, Romano PS. A population-based study of the effectiveness of inferior vena cava filter use among patients with venous thrombosis. Arch Intern Med 2000 160 2033-2041. 

DESIGNING VENA CAVA FILTERS WITH TEXTILE STRUCTURES... 

Delivery of an inferior vena cava filter requires the filter structure to be collapsedand loaded into a sheath that fits inside a 6-9 French (2-3 mm diameter) size catheter. A guidewire is first inserted into the vein and its position tracked by radiological imaging. 

At this time all commercial vena cava filters are fabricated firan ehber nitinol (nickel, cobalt, and titanium alloy), phynox (nidcel, cobalt, chromium, iron, and molybdenum alloy), or stainless steel wire in various catfaeter sheath sizes raiigii fiom 7-14 French (23 - 4.7 mm diameter). These metals were chosen because fiiey are biostable and have low thrombogenicity. This means that blood is less likely to form clots cm the surfiice, and cells are not encouraged to grow around the device. Moreover, nitinol is a thermal shape memory alloy that is self-expanding afier deployment and exposed to txxfy temperature(l]. 

Figure 3. Permanent vena cava filters (left to right) Simon nitinol filter (Bard), Over-the-wire stainless steel Greenfield filter (Boston Scientific), TrapEase filter (Cordis Endovascular), and Bird s nest filter (Cook)... 

Figure S. Temporary vena cava filters Qeft to right) TenqtofiUer II (B. BraunX Gunther filter (Cook), Neuhaus protect filter (TorayX Andieor filter (Boston Scientific)...

Although vena cava filters have been in clinical use since fiie 1960 s, they have not always been safe and effective due to late complications. A number of complications have hem reported in the literature, including recurrent pulmonary embolism (2-5%), inferior vena cava thrombosis (6-30%), access site thrombosis (2-28%X filter migration (3-69%X tilting (15-20%) (Figure 6), penetration of the voia cava wall (9-24%), structural fracture of the filter (1%), and guidewire entrapment (<1%) (Figure 7) [9]. 

Siskin, Inferior vena cava filters , eMedicine , 2005,... 

A Chiou et al., Vena cava filters vdiy, vdien, what, how , Vase Surg Endovasc Ther, 2005 17,329-339. 

Vena cava filter device update . Endovascular TodcQ>, January 2005,68-69... 

H Lorch et al., Efficacy ofpermanent and retrievable vena cava filters Experimental studies and evaluation of a new device , Cardiovasc Intervent Radiol, 2002 25,193-199. 

G Bovyn et al., Long-duration temporary vena cava filter A prospective 104-case multicenter study , J Vase Surg, 2006 43,1222-1229,... 

B Matthews et al., Inferior vena cava filter placement Pre-insertion inferior vena cava imaging , The Annual Meeting Southeastern Surgical Congress, Savannah, Georgia, 2003. 

T Kinney, Update on inferior vena cava filters , Vase Interv Radiol, 2003 14, (4) 425-440. 

D Imberti, Retrievable vena cava filters a review , Current Opinion in Hematology, 200613,351-356. 

H Lorch et al., Current practice of temporary vena cava filter insertion A multi-center registry , JVIR, 2000 11,83-88. 

The standard site for the placement of a vena cava filter is below the renal veins in the IVC. However, due to sizing limitations or when there is a high risk of releasing emboli from the kidneys, vena cava filters can also be placed in the suprarenal position (Fig. 17.1). There are three approaches to their percutaneous insertion and delivery. Generally, noninvasive access through a femoral vein is most frequently used (82%),but alternatively, jugular,subclavian, and antecubital approaches have also been found to be clinically successful (Fig. 17.1). ... 

Retrievable vena cava filters (a, b) GuntherTulip filter (Cook Medical), (c) Recovery filter (Bard), (d) Optease filter (Cordis Corporation). 

Complications with current vena cava filters... 

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