Places in the Heart: Porcine Valve Factory : Assembly of Pig Valve Is Series of Delicate Operations--Touched and Retouched
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.
“It’s not a haphazard process. We send technicians to the slaughterhouses to train the people there how to cut out what we need without damage. Naturally, they cull out the bad hearts too.”
“Pigs have a lot of the same diseases humans do,” says Suzanne Latimer, marketing communications manager. “After all, they overeat and get no exercise. . . . “
The pertinent parts of the heart, then, are air-freighted within 48 hours of slaughter, “packed in chests with ice and saline solution,” says Whitehair--”Igloo chests, just like you carry your beer in.”
Behind another glass partition, a tray of newly arrived hearts sits on a lab table, looking like the makings of the world’s largest haggis. The hearts await trimming, another fastidious, demanding series of steps that whittle them down to the thin valve itself.
Trimmed, the valves are immersed for 14 days in a liquid solution consisting mainly of gluteraldehyde--the “fixation” process.
“The process insures against the human body’s rejection response,” Whitehair explains. “The tissue is ‘tanned,’ or ‘fixed’--rendered biologically inert.
“No,” she assures the visiting valvee, “it doesn’t matter how long a pig lives, because we’ve chemically altered the valve.
“An analogy would be your belt. A cow may live, say, 20 years, but a leather belt, having been tanned, will last a lot longer.”
The final stages of assembly take place in another glassed-in area, where several dozen more women fit, then sew, the “fixed” valves into the stents.
If possible, the operation here is more meticulous, more precise than the making of the frames. And more frustrating.
“If you watch long enough, you’ll see some ladies crying in there,” says Ton-That. “It’s like tuning your car. They trim delicately, then trim some more, always trying to get a valve of a particular size to fit perfectly into the stent.
“Maybe you work two, three hours on it. Then, by a slight slip of the hand, you make a tiny hole in it, and it has to be scrapped.”
What with trimming, fixing, sewing, visual inspections and an exacting series of leak and flow tests, American Edwards rejects 80% of the valves it receives from the slaughterhouses.
Nevertheless, as the world’s largest supplier of porcine valves, AEL ships 30,000 a year to hospitals all over the world (at a cost of “in excess of $2,000”)--valves so delicate that even in the stent they weigh but four grams, or one-seventh of an ounce.
Delicate too are the women who construct the precious devices--the antithesis of the assembly line. AEL’s is an intensely personal operation, so personal that the visiting valvee is treated to a meeting with the women responsible for his particular valve--for his life.
Around a boardroom table, on their own time, sit Young A. Oh, Cam Quy Ton, Thong Lu, Hiroe Stratham, Tung Lam, Jacklyn Bui, Abby Pimienta, Tina Nguyen and Adeline Kilongan.
“They’ve been so excited about meeting you,” says Latimer. “They don’t get many chances to see the--the finished product.
“It’s very rewarding to us to see you here, and well,” says Ton-That.
“We feel our responsibility,” says Tung Lam. “We take a real pride in our work.”
“It’s a very exciting environment,” says Rob Michiels, vice president of sales and marketing. “Once you get into it, you find it difficult to step away from.
“We’re constantly experimenting, improving, working toward--sure, the ‘perfect valve.’ ”
“Oh yes,” says Ton-That to the honored valvee, “just in case you were wondering, your valve came from a pig in Warren, N.J.”
The Valvee, a native New Yorker, considers the pig and decides to forgive him his origins.
From the back of his mind, a ditty, penned by author/valvee Grizzard, struggles to get out:
I love you, baby, sorta
Deep down in my aorta.
