A Medical Device Daily

Combining ultrasound energy and thrombolytic drugs appears to dissolve blood clots in leg veins and arteries faster and more often than use of fibrinolytic agents alone, researchers said during the 18th annual International Symposium on Endovascular Therapy (ISET), ongoing this week in Miami Beach, Florida.

The ultrasound technology is that of Ekos (Bothell, Washington), with the study report made by Thomas McNamara, MD, chief of vascular and interventional radiology at UCLA Medical Center (Westwood, California).

The study detailed 99 attempts to dissolve clots in the legs of patients; 66 of the clots were peripheral artery occlusions, and 33 were deep vein thromboses. After 17.5 hours of therapy, 88% of the artery clots were dissolved by the combination approach. In comparative studies, 68% of clots were dissolved after 24.4 hours of therapy with fibrinolytic agents alone.

The Ekos device is a catheter lined with tiny transducers smaller than grains of rice situated on a hair-thin wire. The ultrasound energy helps push the drug also introduced through the catheter away from the device and into the clot, which is altered by the ultrasound as well.

Each device has from six to 30 transducers, depending on the size of the clot. When the drug is delivered, the transducers emit high-frequency, low-energy ultrasound waves to both loosen up the fibers and force the drug throughout the clot. The more fibrin the drug touches, the better and faster the clot dissolves.

Blood clots that form in the legs or pelvis may result in amputation of the feet or legs, and can be fatal.

“The ultrasound energy actually changes the structure of the clot,“ said McNamara. “It widens the fibrin mesh allowing recombinant clot-busting drugs to enter the clot and dissolve it.“

There was only one major bleeding incident with the combination treatment, while historically there can be as much as 18% of bleeding incidents, he noted.

He called the studies “preliminary,“ and because the study did not employ control groups there was no calculation of statistical significance. “However,“ McNamara said, “I've been working in this field for a long time, and I think these differences are real. This appears to be a better treatment for these potentially deadly clots.“

Among the patients with vein clots, 23 of the 33 patients about 70% achieved complete elimination of the blockages in about 23 hours. Conventional treatment results in about 31% to 38% lysing of the clots, although it takes up to 53 hours to achieve those results. Major bleeding was also more than halved when compared to conventional treatment studies, McNamara said.

Overall, ultrasound-enhanced delivery showed a 28% improvement in dissolution of clots and a 92% reduction in bleeding, compared to conventional treatment.

“High-frequency ultrasound enhances the ability of the drugs to break up these clots,“ said Keith Sterling, MD, chief of cardiovascular and interventional radiology at Inova Alexandria Hospital (Alexandria, Virginia). “It really does speed up the process.“

“This device is exciting because it enhances the ability to dissolve clots and may lead to a procedure with fewer complications,“ said James Benenati, MD, medical director of the peripheral vascular laboratory at Baptist Cardiac & Vascular Institute (Miami), one of the sites in the ongoing study. “It also may have the advantage of allowing the procedure to be done much more quickly, which will save physicians and hospitals time, and lower the cost of the procedure.“

The current infusion process can take up to 48 hours, and the longer the infusion, the greater the risk of limb- or life-threatening bleeding elsewhere in the body, particularly the brain. Also, patients are immobilized and must be treated in monitored care beds.

In other ISET news, Boston Scientific (Natick, Massachusetts) reported positive results from its Renaissance trial, designed to study the safety and effectiveness of the Express SD Renal stent in the treatment of renal artery disease.

Renaissance is a prospective, single-arm, multi-center study involving 100 patients in 14 U.S. sites, with the primary endpoint restenosis at nine months. The restenosis rate was compared to a benchmark of 40% determined by a literature review of similar endpoints in patients undergoing balloon angioplasty of the renal artery.

Krishna Rocha-Singh, MD, of Prairie Cardiovascular Heart Institute (Springfield, Illinois) and the study's principal investigator, reported a restenosis rate of 21.3%, significantly lower than the 40% benchmark.

“The Renaissance study provides critical insight into the occurrence and treatment of renal artery disease,“ said Rocha-Singh. “Physicians have seen poor results treating this disease with a balloon alone, so it's gratifying to see an improved outcome when incorporating the Express SD Renal stent.“

John Pedersen, president of Boston Scientific's Peripheral Interventions business, said the results would support a regulatory application with the FDA. “It will be the first low-profile stent specifically approved for use in the renal arteries, which should allow physicians to deliver the stent in more complex cases.“

Rocha-Singh also reported excellent safety results, with a major adverse event (MAE) rate of 10.5%, including no in-hospital events and no reported stent thromboses. In addition, he reported a low target lesion revascularization or repeat procedures due to re-narrowing of the vessel rate of 8.4%. The trial also demonstrated excellent follow-up success with 93 of the 100 patients having ultrasound performed at nine months post implantation of the stent.

“A 93% follow-up rate demonstrates excellent execution and integrity of a clinical trial,“ said Rocha-Singh. “We will continue to carefully monitor the progress of these patients with follow-up at two years and yearly out to five years. This will help us gain a better understanding of the long-term effects of the Express Renal SD stent in treating renal artery disease.“

Renal artery disease is the narrowing of the blood supply to the kidneys due to atherosclerosis, or the formation of plaque within the arteries. When the kidneys have a normal blood supply, they filter toxins from the blood and help to keep blood pressure in the normal range. Renal artery disease may lead to high blood pressure, poor kidney function or even kidney failure and dialysis.

Renal artery disease can be treated surgically or less invasively via angioplasty, or the placement of a balloon at the site of the lesion.

The balloon is inflated, compressing the plaque against the walls of the artery, and then removed. Renarrowing of the arteries is common with this treatment method, however, leading to the study of stenting as a treatment option. A stent is an expandable metal mesh tube that remains in the artery after the removal of the balloon that supports the vessel wall to maintain blood flow through the newly opened vessel.

ISET, presented by the Baptist Cardiac & Vascular Institute, is attended by more than 2,000 physicians, scientists and industry professionals from around the world. It focuses on multidisciplinary approaches and demonstrations of procedures and devices for the diagnosis, treatment and prevention of cardiac and vascular disease.

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