Other Vascular Interventions

Transcatheter Biopsy

In its simplest form, transcatheter biopsy is merely the sampling of venous blood directly from an organ as described in a previous section. Tissue samples may also be obtained by transcatheter techniques. The overwhelming majority of these procedures are performed in the liver for diffuse hepatic disease. Using a right internal or external jugular approach, a guiding catheter is taken through the right atrium and into the right or middle hepatic vein. A blunt metal cannula is passed through the catheter and an 18 or 19 ga. slotted biopsy needle is introduced through the cannula. The biopsy is then performed through the vein wall. This technique is generally reserved for patients who are not candidates for percutaneous biopsy because of coagulopathy or ascites. This technique is also used in patients for whom percutaneous biopsy is not contraindicated, but who also need a hemodynamic evaluation of the hepatic venous system and measurement of portal to systemic pressure gradients. The transvenous biopsy technique is not appropriate for focal liver disease, such as hepatoma or metastatic disease, where imaging guidance into the lesion is necessary.

Transcatheter biopsy has also been useful in differentiating portal vein thrombosis from portal vein invasion by hepatoma. The procedure is similar to that described above except that a sharp metal cannula is used and puncture is made into a portal vein. Once portal venous entry has been gained, a catheter and guide wire are maneuvered into the tumor/thrombus. The guide wire is removed and aspiration biopsy is performed through the catheter.

Transjugular Intrahepatic Portosystemic Shunts

The transjugular intrahepatic portosystemic shunt (TIPS) procedure is an interventional radiology alternative to conventional portocaval shunting in patients with advanced liver disease and portal hypertension. TIPS was originally described by Rösch in 1968, and developed as a technique in humans by Colapinto in the early 1980's. Although these early TIPS were technically successful, these shunts suffered early failure because of elastic recoil of the liver parenchyma. Consequently, after an initial burst of enthusiasm, the TIPS procedure was practically abandoned. The recent introduction of vascular stents capable of opposing parenchymal recoil and maintaining shunt patency has led to a marked resurgence of interest in this procedure. That interest has been reinforced by the dissemination of liver transplantation programs and the important role of TIPS as a temporizing measure in patients awaiting transplantation.

Liver transplantation is now the treatment of choice for suitable patients with end stage liver disease. Many patients considered for transplantation have chronic portal venous hypertension and variceal bleeding, yet continue to have adequate liver function. Surgical portosystemic shunts have been used for years in such patients to control variceal hemorrhage. However, alterations in the extrahepatic vascular attendant to surgical shunts may add considerably to the technical difficulty of liver transplantation. TIPS, being entirely intrahepatic, avoids that problem and is thus ideally suited for patients who are potential liver transplant candidates. Because of its minimally invasive nature (compared to open surgical shunts), TIPS may also be the procedure of choice for portal decompression in patients who are not transplant candidates.

Many patients referred for TIPS are poor surgical risks for portocaval shunting. The majority of these patients have had recurrent variceal hemorrhage and multiple sclerotherapy sessions. Other patients have severe ascites or hepatic hydrothorax which is refractory to medical therapy. TIPS is also indicated as an emergency procedure in patients with active variceal hemorrhage that cannot be controlled by pharmacological or endoscopic means. However, these patients are often critically ill. Many are receiving a variety of drips including vasopressin, dopamine, etc. in addition to plasma expanders, crystalloid and blood products. The mortality rate in such patients is extremely high.

The TIPS procedure is technically demanding. It consists of creating a passage between an hepatic vein and an intrahepatic portal vein, entirely within the liver parenchyma. In the typical procedure a guiding catheter is introduced via the right jugular vein and, after traversing the right atrium, positioned in the right or middle hepatic vein. A puncture is then made through the hepatic vein wall and into an intrahepatic portal vein branch using a Colapinto or Rösch-Uchida transjugular portal venous access needle. Once portal vein entry is achieved, a guide wire is introduced and the communication is established by balloon dilatation of the parenchymal tract. Metallic vascular stents are then implanted throughout the tract and extending into both the portal and hepatic veins. Finally, the stented tract is redilated with an angioplasty balloon of appropriate size to achieve the desired reduction in portal venous pressure.

The most common complication during a TIPS procedure is puncture through the liver capsule. Capsule perforations are generally innocuous and may be quickly sealed with gelfoam and/or coil embolization. Rarely, the puncture will enter the portal vein in an extra-hepatic location. If this is not recognized, balloon dilatation of the tract will result in portal vein laceration with significant intra-abdominal hemorrhage. This is a potentially fatal complication that requires urgent completion of an intrahepatic TIPS to reduce portal venous pressure. Extending the stent across the site will seal the laceration but may complicate subsequent liver transplantation. This complication is avoided by careful evaluation of the patient's anatomy prior to the procedure. Cardiac rhythm disturbances are not uncommon during TIPS since the entire procedure is done through the right atrium. Forceful manipulations, such as when the balloon is first passed through the parenchymal tract, may cause the catheter to buckle in the atrium and prolapse into the right ventricle. Irritation of the conduction system due to catheter prolapse may produce ectopy, ventricular tachycardia or even ventricular fibrillation. Consequently, close monitoring of the EKG is important during these manipulations. The other significant complication is fluid overload which potentially can progress to pulmonary edema. For the most part, this will not occur acutely during the procedure. However, once the shunt is established, the portal system quickly decompresses into the systemic venous system and central venous pressures can rise dramatically. Diuretics, morphine, and oxygen constitute the mainstay of treatment. Ionotropic medications such as digoxin may be required. Hepatic encephalopathy is a relatively common early post-procedure complication, seen in 10-30% of patients. Approximately 20% of patients receiving TIPS will develop new onset or exacerbation of hepatic encephalopathy that, in most cases, responds favorably to lactulose and dietary measures.

Following completion of a TIPS, a vascular sheath is left in place to maintain jugular venous access. An abdominal ultrasound with Doppler is done as a baseline examination, and the patient is sent to ICU for overnight monitoring. If the patient remains stable and repeat ultrasound the following morning shows shunt patency, the sheath may be removed and the patient transferred to the floor. Most patients can be discharged from the hospital within 48 hours of an elective TIPS procedure.

Recent experience suggests that TIPS and endoscopic sclerotherapy and banding are complementary procedures for the management of patients with bleeding from esophageal varices. Sclerotherapy is readily available in most hospitals and usually effective in achieving immediate control of hemorrhage. However, sclerotherapy does not address the underlying problem of portal hypertension, and recurrent hemorrhage is relatively common. Consequently, sclerotherapy should be the first line of treatment in these patients. However, once the acute bleeding has been stabilized, the patient should be referred to a center for a TIPS procedure to decompress the portal venous system. Attempting to manage recurrent variceal hemorrhage by repeated sclerotherapy often results in recruitment of new collaterals for portal outflow. These may include gastric and duodenal varices from which hemorrhage may be impossible to control by endoscopic techniques. In such cases, emergency portal decompression, either by TIPS or by surgical shunting, is associated with a very high (>50%) mortality rate. The 30 day mortality rate for elective TIPS is less than 2%.

In a review of 100 TIPS procedures performed at the University of Kansas Medical Center, TIPS was shown to be highly effective in reducing elevated portal venous pressure and controlling the complications of ascites and variceal hemorrhage. However, TIPS are prone to intimal hyperplasia and hepatic vein outflow stenosis, and at least 40% of TIPS will require one or more revisions within one year of the initial procedure (overall revision rate of 0.8). Consequently, surveillance is a crucial element of post TIPS patient management. We currently recommend duplex Doppler evaluation of TIPS at 7 and 30 days, and at 3 to 6 month intervals thereafter. Surveillance ultrasound studies must be performed by operators experienced in evaluating TIPS, with careful attention to technique so that valid comparisons with baseline and earlier studies can be made. Sonographic findings suggestive of impending TIPS malfunction should be confirmed by TIPS catheterization with measurement of pressure gradients. If necessary, revision (angioplasty and/or additional stenting) can be done at the time of diagnostic catheterization, usually as an outpatient procedure.

With good surveillance, TIPS has an assisted patency rate of >90%. Unfortunately, TIPS does nothing to alter the underlying hepatic pathology in patients with progressive liver disease. The one exception to this in our experience was a patient with acute hepatic veno-occlusive disease. That patient received a TIPS early in the course of her disease and experienced immediate improvement in hepatic synthetic function. Within 21 days her hepatic venules had recannalized through endogenous fibrinolysis. The TIPS went on to thrombose due to insufficient flow through the shunt, leaving the patient with normal portal venous pressure and a normal liver by all clinical measurements.

Inferior Vena Cava Filters

Pulmonary embolism (PE) is a major cause of death in hospitalized patients. The usual treatment of PE is immediate anticoagulation with heparin followed by coumadin which should be maintained at therapeutic levels for at least six months. The purpose of anticoagulation is to inhibit propagation of thrombus. Anticoagulants are not thrombolytic agents and thus do not treat the embolus that has already occurred.

Many hospitalized patients fail anticoagulant therapy for one reason or another. Some patients continue to have embolic events despite an adequate level of anticoagulation, while others experience complications such as bleeding or heparin induced thrombocytopenia. Anticoagulation may be contraindicated due to a patients underlying disease. Heparin may be ineffective in patients with protein C or protein S deficiency, or other hypercoagulable states, and may actually precipitate a state of intravascular thrombosis due to platelet aggregation (white clot syndrome) in patients with anti-heparin antibodies. Cases such as these represent the major indications for placement of an IVC filter.

In addition to the indications discussed above in patients with PE, IVC filter placement may also be appropriate in certain patients who have not had a documented embolic event. Patients with septic thrombophlebitis, nonadherent thrombus in the common femoral and/or iliac veins and/or IVC, and patients with documented DVT who, because of minimal pulmonary reserve, would not survive a PE, should all be considered for IVC filter placement.

There are currently five different filters available in the U.S., and several others under investigation here and in Europe. No filter has shown clear superiority in either efficacy or complications. The most widely used filter until recently was the stainless steel Greenfield device, which required a 24 Fr. (8 mm) sheath for placement. The large size of the venous entry required for this filter was responsible for a high incidence of entry site complications. Newer filter designs use 9 to 12 Fr. entry systems and appear to have a much lower incidence of entry site problems such as hematoma and venous thrombosis. All of the available filters have a trapping efficiency of about 85%, and an incidence of symptomatic recurrent PE of 1-5%. The incidence of IVC occlusion is less then 5% in most reported series.

In the past, IVC filters were placed through an internal jugular venous cut-down, generally in the operating room using poor quality portable fluoroscopy and often without adequate evaluation of the IVC and its tributaries. This technique occasionally resulted in malpositioned filters or filter migration subsequent to placement in an oversized IVC. Correctly positioned, the cephalic end of the filter should be at the level of renal vein inflow. The rationale for this is that the filter may trap a large thrombus resulting in caval occlusion. Aberrant positioning below the level of the renal veins leaves a potential dead space which, in turn, becomes a site of thrombus propagation within the unprotected portion of the IVC. Aberrant positioning across or above the renal veins places the patient at risk for renal vein thrombosis. Occasionally, thrombus will extend into the IVC for a variable distance. If the degree of caval thrombosis is such that there is inadequate space below the renal veins, the filter can be placed in a suprarenal location with its tip at the level of the hepatic vein inflow. Other potential filter misplacements occur when one or more of the struts enter an hepatic or renal vein. In this situation the filter is both malpositioned and tilted in the cava. In vitro studies have shown a significant reduction in clot trapping efficiency when Greenfield-type filters are tilted in excess of 15 degrees.

The Bird's Nest Filter can accommodate caval diameters up to 40mm. All of the remaining IVC filters available are limited to caval diameters of 28mm or less. An estimated 85-90% of all individuals will have an IVC diameter within that range. Placement into an oversized cava places the patient at risk for filter migration or embolization into the right heart with attendant risks of arrhythmias and perforation with cardiac tamponade. There have been a number of cases reported where thoracotomy was necessary to remove an embolized filter. In a few such cases the filters were removed using catheter based retrieval techniques. There have also been a few reported cases of filter embolization in patients undergoing abdominal surgery within 72 hours of filter placement. These patients all had IVC diameters approaching the 28mm limit. It is believed that fluid loading and positive pressure ventilation during anesthesia resulted in distention of the IVC with release of a poorly attached filter. Because of this, some authorities recommend the Bird's Nest device in patients scheduled for surgery following filter placement.

Radiological placement of IVC filters began in the mid 1980's using the 28 Fr. Greenfield device. Lower profile devices became available in 1988. Radiological placement begins with an IVC-gram to measure the caval diameter, assess for the presence of caval thrombus, and accurately identify the position of the renal vein inflow. Following the cavagram, the filter is introduced, positioned, and deployed under high resolution fluoroscopy. Aberrant positioning under radiological guidance is extremely unusual, and inappropriate matching of filter to caval size does not occur.

Temporary IVC filters are now in use in Europe and Canada. One such device has recently been approved by the FDA and is available for patients requiring short term (<28 day) protection following trauma or surgery.

Central Venous Access

Widespread use of central venous catheters (CVC) began in 1968 with the introduction of total parenteral nutrition. Since that time, CVC have grown in importance, particularly in patients requiring central venous access for chemotherapy, chronic antibiotic administration, infusion of blood products, nutritional support, and in patients who require frequent blood draws but have poor venous access. Large bore, double lumen temporary and "permanent" catheters are used for plasmapheresis and hemodialysis. However, patients requiring these procedures on a chronic basis are generally better served by creation of an arteriovenous fistula or shunt.

Until recently, central venous access services have not been centralized in most institutions. Temporary catheters usually have been inserted at bedside by a treating physician with no formal training in catheterization techniques, while long term tunneled catheters have been referred to surgeons for operative placement. In both circumstances the catheter is inserted blindly and most often without prior evaluation of the central venous system. Moreover, the majority of catheters placed operatively are large bore catheters that are inappropriate to the needs of the patient. Consequently, the incidence of CVC complications is relatively high with thrombotic complications occurring in 30 to 48% of patients.

Because interventional radiologists have extensive training and experience in image guided vascular catheterization techniques, central venous access services have become an integral part of interventional radiology practice at many major medical centers. Tunneled long term catheters, short term catheters (PIC lines), and subcutaneous central venous access ports can all be inserted in the interventional radiology suite with fewer complications and significantly lower overall cost compared to operative placement. CVC insertion by interventional radiologists begins with extremity and central venography to assess for aberrant anatomy or pre-existing central venous thrombosis. This study eliminates the more common causes of failure during surgical CVC insertion procedures. The information provided by venography is also used in determining the appropriate catheter size based on the diameter of the vein.

Selection of a particular type of CVC should be based on the intended purpose of the catheter, the frequency and expected duration of use, and the size of the vein at the proposed site of entry. Hickman catheters, for many years the mainstay of "permanent" central venous access, are an inappropriate choice for the vast majority of patients. Most patients receiving chemotherapy, antibiotics, blood products or nutritional supplements require neither a double lumen catheter, nor a large bore catheter such as a Hickman. Smaller, single lumen catheters result in much less venous endothelial damage and significantly reduce the incidence of catheter-related central venous thrombosis. For short term and frequent use, such as intravenous antibiotic therapy, PIC lines of 4-6 Fr. size are generally recommended. For longer term or intermittent therapy, peripheral or chest wall subcutaneous access ports have both cosmetic advantages and require less maintenance (flushing) while imparting a somewhat lower risk of infection. Temporary large bore tunneled hemodialysis and plasmapheresis catheters can also be placed in the interventional radiology suite. As with the small lumen catheters and ports discussed above, preliminary evaluation of the venous system and image guided positioning of the catheter tip result in fewer complications and a lower incidence of catheter malfunction.

Endovascular Foreign Body Retrieval

Transcatheter retrieval of intravascular foreign bodies has become a relatively common procedure at large centers where invasive hemodynamic monitoring, total parenteral nutrition, infusion chemotherapy and other techniques requiring prolonged vascular catheterization are extensively used. Interest in these techniques among interventional radiologists was initially spurred by the rising complexity of interventions both in and out of the vascular system, and the attendant risk that many of these procedures could result in catheter fragmentation and embolization. Today, interventional radiologists have at their disposal a wide variety of tools and techniques for transcatheter retrieval and manipulation.

Retrieval procedures are most commonly employed in the setting of patients having Hickman or Infusaport type central venous catheters. These catheters are a particular problem in younger and more active patients with catheters placed via a subclavian vein. The belief that shoulder and arm movements result in catheter fatigue and eventual fracture is supported by the observation that the most common site of catheter fracture is in the subclavian vein as it passes between the first rib and the clavicle.

Following fracture, the catheter fragment usually will embolize to the right heart or pulmonary artery. When the catheter is entirely in the right ventricle, cardiac irritation and arrhythmia often occur and will be exacerbated by the retrieval procedure. The rhythm disturbances have the potential to degenerate into ventricular tachycardia or fibrillation. While a lidocaine bolus and drip may be protective, the best course of action in these cases is to gently manipulate the fragment with a catheter until it embolizes into the pulmonary artery. There, the fragment can be captured easily in a loop snare or basket, with little risk of severe cardiac complications. Once captured, the fragment is brought out through the venous entry site. Care must be exercised during removal as the catheter fragment can be transected by the retrieval device, resulting in embolization of small fragments that can be extremely difficult to recapture.

Occasionally, central venous access catheters become malpositioned. Techniques analogous to those used in retrieval procedures may be employed to capture and relocate the catheter tip. Typically, the tip of the central venous catheter somehow ascends the internal jugular vein. Using a femoral vein approach, a pigtail catheter is taken through the right atrium, SVC, and into the brachiocephalic vein. The pigtail shape at the catheter tip is controlled by a guide wire, and the loop of the pigtail is made to form around the shaft of the malpositioned catheter. The pigtail shape of the catheter is then maintained by a special guide wire, called a deflecting wire, which coils tightly at its tip when engaged. The pigtail and deflecting wire are pulled down as a unit, dragging the central venous catheter into the SVC.

A variety of other objects such as guide wires and wire fragments, stents, and embolization coils may require retrieval techniques. In one unusual case, an inmate of a local psychiatric hospital with a penchant for self inflicted wounds managed to insert a broken safety pin into her jugular vein. The pin embolized to her right ventricle and was subsequently retrieved using a looped snare from a femoral vein approach

Many complex interventional procedures employ retrieval techniques in order to obtain necessary access. The common denominator in these procedures is that a guide wire is introduced via one access (arteriotomy, nephrostomy, etc.), then captured and retrieved via a second access. With both ends of the guide wire controlled, passage of catheters and other over-the-wire devices is greatly facilitated.