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Places in the Heart: Porcine Valve Factory : Assembly of Pig Valve Is Series of Delicate Operations--Touched and Retouched

May 19, 1987|DICK RORABACK | Times Staff Writer

Consider the pig. He toils not, neither does he spin.

He totes no barge, lifts no bale. He counts no calories, and in the end he pays the price, his worth measured in sausages.

To most, the pig is the point man for the BLT; to others, Eric Dickerson's running mate. To hundreds of thousands, though, the pig is a hero (or heroine, as the case may be). A lot closer to the heart than the spouse, the child, the lover. A donor of the aortic valve that quite literally keeps them alive.

The pig's heart closely approximates that of the human, both in size and conformation. Possibly in temperament; who can tell?

Its aortic valve is the piece de resistance, again quite literally.

The valve opens with each pump of the heart, then closes momentarily to prevent blood from seeping back into the left ventricle, opens again to enable the blood to rocket into all those bodily crannies that need it. Like, everywhere.

Humans--pigs too, for that matter--are susceptible to diseases of the valve: calcification; stenosis, or narrowing; congenital malformation. Blood begins to leak back into the ventricle.

Instead of the normal "ka-THUMP, ka-THUMP," the heart, as heard through a stethoscope, now goes, "ka-THUMP, shhhh; ka-THUMP, shhhh." Sometimes even, "ka-THUMP, wibbledy-wibbledy phew." It's time for Porky.

Or time for a mechanical valve. About 50% of some 800,000 aortic-valve recipients--hereafter known as valvees--opt for the man-made prosthesis. There are advantages and disadvantages to each choice.

The mechanical valve is built to last; the porcine valve (bioprosthesis), developed within the last 15 years, wears out after 10, give or take, and must be replaced.

On the other hand, the plastic valve leaves the bloodstream susceptible to clotting. Consequently, the valvee must take blood thinner each day. Blood thinners produce side effects, usually more annoying than debilitating. Real or imagined, they include sensitivity to cold, hair loss, excessive wind. . . . Most irritating, perhaps: the mechanical valve clicks, audibly.

The pig valve runs silent, runs deep. One can fall asleep counting sows, not clicks.

Behind a glass partition on the second floor of American Edwards Laboratories in Irvine, four dozen women in white gowns and blue shower caps are sewing their hearts out. Intent and absorbed, they are bent over their work, make intricate stitches that would be the envy of Balenciaga.

They are not sewing pigs' valves--another contingent downstairs handles that end. Rather, they are fashioning "stents"--or frames, or cradles, if you will--into which the valve itself will be sewn.

The porcine valve cannot be stitched directly into the aorta. It is too delicate. "It would get floppy and not open and close correctly," says Anne Whitehair, American Edwards market manager. "The frame provides support," and the silicon rubber ring sewn into the frame "gives a foamy, spongy place for the surgeon's suture to bite."

Skeleton of the stent is a thin wire twisted into the outline of a shark's molar. (The wire, incidentally, shows up on X-rays, and on airport metal detectors. Explain that to the security guard.)

The wire is strong but flexible, with a "memory" that makes it spring back after yielding to the powerful surge of blood from the heart.

"The wire is designed to outlast the valve," Whitehair says. A visiting valvee takes small comfort.

Next, a thin sheet of Mylar, precision-cut by laser, is added to the wire, reinforcing the stent and bearing the serial number of the valve.

Like the ducks served at Claude Terrail's Tour d'Argent in Paris, each valve bears a number.

When the valve is worn out, it is "explanted" (Whitehair's marvelous euphemism) and returned to American Edwards Laboratories, which learns from its history and helps the lab to pursue its quest for the "perfect valve."

"A bit like tagging a fish," suggests the visiting valvee. "Exactly," says Whitehair, "or banding a bird."

The rest of the stent-making process consists of incredibly painstaking stitchery. Equally incredibly, it is all done with a single monofilament thread, after the fashion of a bald man combing his last hair into a dainty pompadour.

"It's all done by hand," Whitehair marvels. "Look at the handiwork! No creases, no bunching. A work of art."

Indeed it is. And on to the pigs.

"I was afraid they kept the hogs in a pen out behind the hospital," writes valvee Lewis Grizzard in the hilarious account of his surgery: "They Tore Out My Heart and Stomped That Sucker Flat."

"I've been prepared for surgery and the doctor says to an orderly, 'Leon, go out to the hog pen and get me a valve.' "

In an area popularly known at American Edwards Laboratories as "the tunnel," the pigs' hearts are prepared for mounting on the stent.

"The hearts come from a variety of slaughterhouses all over the U.S. and abroad," says Cuong Ton-That, manager of manufacturing.

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