Making clot-resistant coronary grafts.

Last year, almost 20 percent of the 300,000 coronary bypass operations in the United States were performed to replace earlier bypass grafts fashioned from plastic or from patients' veins, notes surgeon Michael R. Phillips of the Mayo Clinic in Rochester, Minn. Phillips reports a new procedure for preparing synthetic grafts that may not only extend the useful life of such plastic tubes but even make them preferable to grafted veins.

Most grafted veins tend to clog up within 10 years, Phillips says, probably because they harbor the same fatty deposits that had clogged the original artery. Surprisingly, life-threatening fatty blockages also can develop in plastic grafts.

In an effort to get around these problems, Phillips is adapting for use in the heart a hybrid graft now being tested in human leg arteries. Unlike all-plastic grafts, the inside of this semipermeable tube is "sodded" during surgery with a uniform covering of epithelial cells, which occur in a range of tissues, including the inner surface of natural blood vessels, and seem to inhibit plaque formation.

Phillips harvests the cells from nonvascular tissue at the beginning of the operation. After bathing the interior of the plastic with blood serum, he injects these cells into the tubing. "The trick," he says, "is to apply pressure-some 3 to 5 pounds per s quare inch for about 7 minutes." The cells then adhere and begin secreting chemicals that maintain their health.

To further inhibit plaque deposits, Phillips bridges segments of dog hearts with his graft in a way that promotes unusually high volume and high velocity flow. He's shown in nine dogs that their epithelial lining remains healthy for at least 5 weeks.