BBI Contributing Writer

SCOTTSDALE, Arizona Endovascular specialists from around the globe gathered here in early February for the 16th annual International Congress for Endovascular Interventions. The program, which attracted 628 interventionalists, featured updates on cardiovascular surgical techniques such as autologous myoblast transplantation. Outcomes studies and recommendations for endovascular aortic aneurysm replacement also were presented. Companies (attendance included 210 representatives from industry) and their technologies for treatment of varicose veins, thrombolysis and deep vein thrombosis were evaluated.

Myocardial infarction (heart muscle death) occurs when coronary arteries become blocked and the surrounding heart muscle doesn't get the blood and oxygen necessary for survival. In many situations the blockage can be opened by angioplasty. In some instances open repair of the blocked arteries is necessary that procedure is coronary artery bypass grafting (CABG). When a CABG procedure is in process, the heart is in the surgical field. Cardiovascular surgeons are beginning to repair myocardial infarction with the implant of new cells autologous myoblast transplantation (AMT).

Nabil Dib, MD, of the Arizona Heart Institute (Phoenix, Arizona), spoke about the safety and feasibility of AMT in patients undergoing CABG procedures. These patients were enrolled in a U.S. multi-center trial over a one-year period. Patients were eligible for the study if they had experienced a previous myocardial infarction and had a left ventricular ejection fraction of less than 30%. Fractions less than 55% indicate a heart with weakened contraction capability.

To accomplish AMT, surgeons removed a skeletal muscle biopsy of about 2 grams from each patient. The muscle biopsy cells (myoblasts) were isolated and expanded over a period of two to three weeks. Between three and 30 direct injections of myoblasts were delivered into the area of infarction at the time of surgery using one of four escalating cell doses ranging from 10 million cells to 300 million cells. Twelve patients underwent AMT combined with CABG in Dib's study, with a mean age of 57. Myoblast cells were successfully delivered in all subjects with no injection-related complications. At nine months' follow-up, echocardiography, positron emission tomography and magnetic resonance imaging scans showed evidence of viability of the new cells in the area of grafted scar. The mean improvement in ejection fraction was from 22.7% to 35.9 %. Dib concluded that improvement in viability of the transplanted myoblasts and improvement in the heart wall thickness is encouraging and more clinical trials are warranted.

Endovascular aortic aneurysm repair (EVAR) is a relatively new procedure, first performed in 1995 at the Arizona Heart Institute. The procedure involves placing a cloth-covered stent-graft within the aneurysm using a femoral artery access site. Standard open repair involves a major abdominal incision, clamping of the aorta and sewing in a graft. White males over age 55 are at greatest risk for abdominal aortic aneurysms (AAAs), which are among the top 10 causes of death among this group. By age 80, more than 5% of white males will have developed an aneurysm. AAAs occur less frequently in white females and they are relatively uncommon in both African American sexes. Now that the first-generation graft devices have eight years of history, endovascular interventionalists are able to look back at outcomes and suggest improvements in techniques and testing.

At the Miami Cardiac and Vascular Institute (Miami, Florida), Barry Katzen, MD, and his colleagues reviewed charts of 455 patients who had undergone EVAR. The patients were nonrandomized, but consecutive. The patient population was 87% male and 13% female. Epidural anesthesia was used on 78% of the cases. The others were a mix of local anesthesia and a general anesthesia. Successful EVAR was achieved in 96.26% of the procedures. Some 2.2% had to be aborted and 1.5% were converted to open surgical repair.

For those patients where the EVAR was successful, their length of stay (LOS) at the hospital was less than one day. Patients with higher overall risk factors had extended LOS. Perhaps Katzen's most interesting finding involved the female patients in this retrospective study. He found that women get some benefit from EVAR, as do men, but that there may not be a significant difference in survival for these women vs. watchful waiting.

Preclinical device testing needs improvement

Current aortic stent-grafts rely on mechanical fixation because biological incorporation is poor. Late failure of the stent-grafts is usually attributable to mechanical stress. Stent-grafts migrate due to inadequate fixation or as a result of material fatigue. According to Martin Malina, MD, PhD, of Malmo University Hospital (Malmo, Sweden), stents also may break at circumferential or longitudinal "backbone" wires and the graft fabric may tear. He expressed concern that the physical properties of stent-grafts are rarely disclosed and mechanical requirements are not sufficiently considered during preclinical device testing.

According to Malina, aortic stent-grafts must withstand the full longitudinal force of blood flow about 10 Newtons. Fixation competence can be assessed in cadaveric or animal models. Columnar support can be tested in bench models. The safety of a telescopic anastamosis in a modular stent-graft depends on the graft diameter, the length of overlap and friction between the graft components. Other forces work against the successful EVAR. There is both radial and longitudinal motion of the aortic stent-graft. The pulsatile motion is usually in the range of 1 mm in the abdominal aorta and 2 mm in the aortic arch. The pulsatile motion varies greatly between different parts of the stent-graft. The graft fabric moves in relation to the stent skeleton and friction may erode the fabric.

Malina challenged physicians, engineers and manufacturers to consider the mechanical demands on aortic stent-grafts in order to improve fixation and avoid late material failures. He called for standardized testing and reporting. Data regarding proximal and distal fixation, pulsatile motion, material durability and ability to comply with angulation ought to be provided to surgeons who are choosing which stent-graft to implant, he said.

Lucien Castellani, MD, of Trousseau Hospital (Tours, France), believes that in coming years, when the complications related to aortic stent-grafts (migration, endoleaks, etc.) are resolved, the biggest risk post-EVAR will be the heart. That is currently true of open abdominal aortic aneurysm repairs. Cardiac events represent the most common cause of significant morbidity and mortality after aortic surgery, with up to 60% of postoperative deaths attributable to coronary artery disease. In single-center experiences and meta-analysis, the average mortality of EVAR in 101 centers including 3,414 patients was reported to be 2.8 % in 2001, similar to open repair.

Adverse cardiac events after open surgery were attributed to excessive stress on the myocardium caused by the combined effects of anesthesia induction, aortic clamping/declamping and operative blood loss with its associated hemodynamic and metabolic changes. Castellani said that hemodynamic alterations associated with EVAR are less severe. Myocardial performance was less compromised and the repair was better tolerated by the heart during EVAR. This may be due to the reduced duration of aortic occlusion. The type of anesthesia also may influence cardiac complications. It seems that the use of local anesthesia for EVAR provides a particular advantage in patients at high risk of cardiovascular complications.

New approaches to dealing with thrombolysis

In recent years, thrombolytic drugs have been used as the primary treatment for acute thromboembolic arterial occlusions. Catheter-directed therapy has been the gold standard. The technique requires several hours and involves systemic dispersal of drugs used to lyse the thrombus. Bacchus Vascular (Santa Clara, California) has introduced a new method for thrombolysis the Trellis Reserve.

This two-balloon device allows the interventionalist to locate, treat and remove the target thrombus by isolating the treatment area. A percutaneous interventional system, Trellis includes an Integral Aspiration Catheter that is inserted over a guidewire into the thrombus. The balloons' radiopaque markers are positioned on either side of the treatment area under fluoroscopy. The distal balloon is then inflated and a dispersion wire is inserted. The proximal balloon is inflated and thrombolytic drugs are infused. The dispersion wire is oscillated to distribute the infused fluid into the treatment area which has been isolated between the two inflated balloons. After 15 minutes of oscillation and aspiration, the balloons are deflated and the wires removed. Trellis is a single-use product that does not require additional drive units, pumps or power injectors. The procedure is covered with existing CPT reimbursement codes.

Bacchus Vascular, which was founded in 1999 by Thomas Fogarty, MD, a noted inventor and cardiovascular surgeon, also is involved in treatment of deep vein thrombosis (DVT). Approximately 300,000 to 600,000 people are diagnosed with DVT in the U.S. annually. The problem initiates in many people as a result of stasis of blood flow, such as that occurring during very long airplane rides. Each year 100,000 people die from complications of DVT. Those complications include pulmonary embolism (PE).

The standard treatment for DVT has remained unchanged for more than 50 years. Anticoagulation therapy is prescribed in 90% of cases to stop thrombus propagation and reduce the risk of PE and recurrent DVT. This therapy involves supportive measures including bed rest, leg elevation and compression stockings combined with a heparin drip that is administered over an average of two to five days in the hospital and is followed by a three- to six-month regimen of oral anticoagulants. Anticoagulation therapy does not, however, dissolve the existing thrombus or immediately restore blood flow.

The Fino mechanical thrombectomy device from Bacchus Vascular provides a minimally invasive approach for rapid disruption and removal of acute and chronic thrombus using a catheter-based device. The product is currently under an approved investigational device exemption study for DVT in the U.S. Unlike existing thrombectomy devices, the Fino design includes a stationary protective basket that scaffolds the vessel wall and valves, allowing the rotating clot-busting element and integrated aspiration to thoroughly remove thrombus debris while preventing pulmonary embolism. Once positioned inside the deep vein at the site of the thrombus, the catheter supplies a basket. Within the basket a rotating coil disrupts the clot and pulls it apart. This direct approach quickly restores venous blood flow without the need for thrombolytic drugs. Fino mitigates damage to venous valves caused by adherent thrombus.

The AngioJet rheolytic thrombectomy system from Possis Medical (Minneapolis, Minnesota), provides another choice for effective and rapid thrombus removal and rapid vessel reperfusion. The AngioJet is useful in removing thrombus in vessels ranging from 2 mm to 12 mm. Water jet technology is used by AngioJet catheters to create a low-pressure zone at the catheter tip drawing in and removing vessel thrombus. There is a choice of catheters to address vessel size and thrombus burden. Using this system, the surgeon can eliminate or reduce dosage and duration of thrombolytic agents.

The AngioJet uses cross-stream technology where saline jets travel backward in the catheter at 360 mph to create a low-pressure zone that, in turn, causes a vacuum effect. The catheter's Cross-Stream windows optimize the drawing action for more effective thrombus removal. Then the thrombus is drawn into the catheter where it is fragmented by the jets and evacuated from the body.

Minimally invasive varicose vein treatment

Fully 50% of those over the age of 49 and 15% to 20% of all adults are affected by varicose veins. The condition develops when venous valves that usually keep blood flowing up toward the heart become damaged or diseased. No treatment currently exists to repair these valves. The only alternative is to re-route blood flow through healthy veins. Traditionally, this has been done by surgically removing stripping the troublesome vein from the leg.

During the endovascular congress, new therapies for varicose veins were displayed. These included products from VNUS Medical Technologies (San Jose, California) and Diomed (Andover, Massachusetts). Not only do these products allow better cosmetic results, but the reimbursement also is better than with surgical stripping of the veins. Representatives of the companies suggested the minimally invasive techniques are reimbursed in the $1,800 to $2,000 range, while traditional vein stripping provides only $300 to $400 in revenue to the surgeon.

The Closure procedure from VNUS Medical is a minimally invasive treatment for superficial venous reflux, which causes pain, swelling and eventually varicose veins in the legs. Closure is done in physicians' offices, surgical centers and hospitals as an outpatient procedure. Local or regional anesthesia is used to numb the treatment area. A thin catheter is then inserted into the vein through an incision near the back of the knee. The catheter delivers radiofrequency energy to the vein wall, causing it to heat, collapse and seal shut. Once the diseased vein is closed, other healthy veins take over. Most patients can resume normal activity immediately.

The Closure system consists of a family of intravascular catheters with temperature sensing ability and specialized bi-polar electrode designs, as well as the software-controlled VNUS RF Generator.

Diomed's EndoVenous Laser Treatment (EVLT) is another technique approved by the FDA for treatment of varicose veins. The physician first uses duplex ultrasound to map out the greater saphenous vein. Then a laser fiber is placed through the vein to the groin following the ultrasound map of the venous system. On activation, the Diomed 810 nm diode laser emits highly targeted energy to seal faulty vein valves shut.

This technique takes 45 minutes on average. Local anesthetic is used at the site of insertion of the laser. There are no scars, no hospitalization and patients return to normal activity immediately, with little or no pain. The company says that 97% of the first-time EVLT treatments are successful.