Intravascular 'sonic lysis' busts peripheral thrombi

For years, interventional radiologists have seen vascular disease management slip through their fingers and into the hands of cardiologists and surgeons. A new ultrasound-based technique, however, may help them reclaim lost turf.

Untreated thrombi causing peripheral arterial occlusive disease (PAOD) or deep vein thrombosis (DVT) may lead to limb amputations, pulmonary embolism, and death. The Lysus infusion system could revolutionize thrombolysis by allowing heparin, alteplase, or urokinase infusions in half the time usually required for recanalization, said Dr. Thomas McNamara, chief of vascular and interventional radiology at the University of California, Los Angeles Medical Center.

The technique seems a natural fit for image-guided therapists who know their way around thrombolytics. It may also help IRs wanting to build a practice to enhance their reputation as experts in treating vascular disease, especially when vascular surgeons and cardiologists appear to be less interested in dealing with these complex, risky procedures, McNamara said.

"You are not going to get everything back," he said. "But you can build on it."

McNamara and colleagues presented in January results from 13 U.S. institutions assessing the device at the 2006 International Symposium on Endovascular Therapy in Miami Beach. Data on 62 patients with PAOD and 33 patients with DVT showed that sonic lysis dissolved 87% and 70% of their clots, respectively, in less than 24 hours. Both patient groups also showed a 92% and 56% reduction in bleeding complications, respectively, compared with conventional treatment.

"This is a big step forward," McNamara said. "When you don't have overnight infusion, you almost never have bleeding."

Conventional thrombolysis entails infusion at the site of the clot that, depending on thrombus size, can take up to two days to complete. The procedure can be expensive and risky. Infusion times correlate heavily with potential limb- or life-threatening hemorrhage.

The study lacks the weight of a randomized controlled study comparing other thrombolysis techniques. Sonic lysis, however, seems to get the job done quicker, saving physician and hospital time and lowering the overall cost of the procedure, said Dr. Suresh Vedantham, an assistant professor of radiology and surgery at Washington University's Mallinckrodt Institute of Radiology in St. Louis.

VALUABLE STEP

Several other mechanically assisted techniques are designed to macerate blood clots and speed up lysis, but they are lengthier and require larger doses of lytic drugs. These devices may toss broken clots deep into the bloodstream, potentially worsening a patient's condition. Their moving parts can potentially damage blood vessels beyond repair. The ultrasound-assisted Lysus system's design seems to overcome these shortcomings, Vedantham said.

"This type of treatment is a valuable step," he said.

The Lysus infusion system comprises a thin wire, beaded with up to 30 tiny ultrasound transducers, sheathed in a conventional catheter. Once it has been inserted in the affected area, the wire emits high-frequency, low-intensity waves, breaking thrombi's fibrin matrix apart as the catheter delivers the thrombolytic. Its manufacturer (EKOS, Bothell, WA) began testing with patients in Sweden six years ago and secured FDA 510(k) market clearance in 2004.