Here's one way to give a dog heart block: Anesthetize it, flip it over, and make an incision along the midline of its chest. Crack open the sternum and pull apart the bone and muscle. It's best to use a dog of medium size, with short hair and a long torso—like a Dalmatian. You won't be able to accomplish very much while the dog's heart is full of blood, so tie off the venae cavae with a tourniquet to block the flow into the right atrium. Remember to move quickly, as the dog can endure only a few minutes in this predicament. (You can buy some extra time by presoaking the animal in a basin of ice water.) Disrupt the heart's conduction mechanism by sewing a single, black silk suture between the tricuspid valve—which separates the right atrium from the right ventricle—and the coronary sinus. Now untie the tourniquet to restore the flow of blood, and you're done. If all goes well, the dog will have lost the ability to pace its own heart.
Every year, 200,000 Americans, and more than 500,000 people worldwide, receive a permanent cardiac pacemaker as a treatment for heart block, bradycardia, or another heart-rhythm disorder. The ubiquity of the pacemaker has a lot to do with the elegance of the procedure now used to implant it: The whole operation takes just an hour or two, it can be performed under local anesthetic, and patients are sent home the next morning. The safe and simple technique—in which doctors make a small incision near the collarbone, open a vein, and slide the pacing leads directly into the heart—was invented more than 50 years ago by Seymour Furman, a young resident at Montefiore Hospital who was spending his afternoons in the dog lab.
Early versions of the pacemaker were crude devices that attached to the external surface of the heart or the front of the patient's chest. A Boston physician named Paul Zoll installed one of the first modern devices in 1952. He wired up a pair of hypodermic needles and plunged them directly into a patient's skin. The pulse generator was a large, external box plugged into the wall. In 1957, an open-heart surgeon at the University of Minnesota started attaching the pacemaker leads directly to the cardiac muscle. This allowed the device to work at a much lower voltage—jolts from the earlier machine had sometimes blistered the patients' skin—but the electrodes were unstable, and it took major surgery to implant them.
Seymour Furman's great insight was to combine the new field of cardiac pacing with a medical procedure that had only recently become mainstream, cardiac catheterization, in which a thin tube is inserted into a blood vessel and advanced into the heart for diagnostic testing. The cardiac catheter had earned its inventers a Nobel Prize in 1956, and one of its early practitioners—Doris Escher—was Furman's mentor at Montefiore. With her guidance, he hoped to pass an electrode through the venous system to the right atrium, where he could pace the heart with more stability and less current than ever before. This would also eliminate the need for chest-cracking, open-heart surgery.
In the fall of 1957, Furman set to figuring out the details of his new procedure in the dog lab. The canine anatomy turned out to be perfect for the experiment: The dog's external jugular vein was large and easily accessible, and provided the catheter with a straight shot into the right ventricle. But before Furman could test the dogs with his new catheter leads, he'd have to open their hearts and induce an artificial block. That procedure proved to be dangerous: Of the 16 dogs assigned to Furman, only four survived.
Bill Miller arrived with his truck at Montefiore Hospital on Thursday, July 1. He'd spent several days carting two goats and 18 dogs across Pennsylvania and New Jersey, and had already sold most of the live cargo to medical centers in Manhattan. He unloaded the remaining animals that afternoon in the Bronx and set off for home.
One of the animals carted into the clinic that day would later be identified as Pepper, the adult, female Dalmatian who had recently disappeared from the Lakavage family's 82-acre farm near Slatington, Pa. While her former owners searched for her in vain, it's likely that Pepper was being stowed in a kennel on the roof of the hospital. It's also likely that her vocal cords were severed when she arrived, leaving her unable to bark and howl in her final hours.
Pepper spent just one night in the Montefiore kennels. Sometime on July 2, she was brought down to the dog lab, anesthetized, and prepped for surgery. A hospital spokesman later told the newspapers that she'd been scheduled to receive an experimental pacemaker.
Click on the player below to listen to Seymour Furman explain the advantages of using dogs for cardiac pacemaker experiments:
By the summer of 1965, Seymour Furman had already worked out the basics of transvenous pacing. His technique enjoyed a significant following overseas, and the American medical device company Medtronic had just introduced its first commercial pacemaker with catheter leads. But there were plenty of problems still to be solved. Batteries died, pulse generators would fail, and patients had to make frequent return visits for follow-up surgeries. That year, the Atomic Energy Commission would start work on a durable, nuclear-powered pacemaker. (The first of these was implanted in a dog in 1969.) When Pepper arrived at Montefiore, Furman was hard at work developing his own, more permanent device, and he needed animals for testing.
On that Friday, Pepper's chest would have been opened like the other dogs, her sternum separated, and her venae cavae tied off to empty her heart of blood. It's not clear when or how the procedure went wrong. Perhaps the surgeons couldn't finish the operation in time to restore her circulation. Or maybe the induced heart block was too severe. Whatever happened, the experiment was a failure: Pepper died on the table.
Warning: This video may be disturbing for some viewers.
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