Membrane adds heat to angioplasty

Miami, FL--In-vitro, animal, and clinical testing have demonstrated that the concept of a thermal angioplasty balloon offers several improvements over conventional angioplasty. Now an angioplasty system based on a convective heat-transfer flexible membrane circuit promises additional advantages over current heated-balloon designs.

Percutaneous transluminal coronary angioplasty opens blocked arteries of the heart. The procedure pressurizes the balloon with a radiopaque fluid to compress and stretch arterial debris and natural arterial wall. Treatment, however, is not without drawbacks:

Because natural collagen in the artery wall and certain lipids contained within the arterial plaque are known to soften at about 48C, heated angioplasty can open debris-laden arteries at lower-than-typical pressures and promote thermal reformation. This reformation, in turn, can reduce the incidence of recoil and restenosis.

A new method for heating the balloon fluid, developed by Michael Fine and Jeff Wilkinson of Cordis Corp., a Johnson & Johnson Company, improves upon current heated-balloon technology. Instead of using radio frequency or laser energy, the Cordis technique relies on a thin, flexible heater. This flexible-circuit heater wraps around the inner shaft within the balloon, its spiral shape facilitating vessel navigation.

A custom-extruded, flat electrical cable transfers energy to the heater. The PTFE-insulated cable consists of two flat 7.5 x 2.5-mil conductors and two 2.5-mil "K"-type thermocouple wires. Inside the balloon, a welded thermocouple provides active temperature feedback.

Purely convective heat transfer from the membrane, Fine says, produces a much more uniform heat distribution to the vessel wall than comparable designs that rely on radio frequency energy. Additionally, the flexible heater is fully activated by less than 9V dc. Typical power requirements are about 2.25W compared to 25 to 45W for RF and laser power sources.

"Since the membrane heater is powered by dc," Fine explains, "the system control unit can run off rechargeable batteries." A portable control box also reduces UL and IEC-601 requirements for hospital use.

Additional details...Contact Stephen Rowland, Cordis Corp., Box 025700, Miami, FL 33102, (305) 824-2000.