Many Paths To The Pacemaker
UNTIL THE AGE OF SEVENTY -six Frank Henefelt of Buffalo, New York, had led an active life. He had been a parts inspector for an optical firm and before that the chief tester for the old Fierce-Arrow automobile company. In retirement he could still mow his lawn or climb a ladder to install screens. “I was one hundred percent,” he said—until the day in 1959 when he began having blackouts. “I had one while I was in the bank, another down in the cellar,” he later told an interviewer. “I’d fall without warning, and I bumped my head so hard a few times—actually fractured my skull once—that I got a football helmet to wear.”
Henefelt had developed a disorder known as complete heart block, in which the heart’s own electrical pulse fails to reach the ventricles, its main pumping chambers. Heart block is a progressive disease and carries a grim prognosis. Deprived of their usual signal, Henefelt’s ventricles beat on their own thirtytwo times per minute. When they failed to deliver enough oxygen-rich blood to the brain, he would collapse. These incidents were not ordinary fainting spells but what heart specialists call Stokes-Adams attacks. Their onset indicated that Henefelt’s heartbeat was defaulting more and more often. Over a period of months Stokes-Adams attacks typically grow more prolonged and more frequent. The ventricles sometimes stop beating entirely. Eventually a sustained episode of ventricular standstill would probably have killed Frank Henefelt.
Fortunately there is a remedy for Henefelt’s condition. If you attach a pair of wires to the heart and connect them to an electrical source for a fraction of a second, the cells of the heart will be depolarized, and the heart will contract. Repeat this stimulation about once a second, and the most dangerous symptoms of heart block may disappear. Today half a million men and women in the United States, most of them over the age of sixty, carry implanted cardiac pacemakers that take over the duties of the natural conduction system (the network of specialized cells that transmit electrical impulses to all parts of the heart) by artificially stimulating the ventricles to beat on schedule. Tens of thousands of the devices are implanted each year in this country alone. Frank Henefelt, back in 1960, became the first recipient of a successful implanted pacemaker.
BECAUSE OF ADVANCES IN microcircuitry, today’s pacemakers can do much more than merely deliver stimulating impulses. As manufacturers emphasize in their advertisements, the pacemaker has become an implanted computer that medical personnel can interrogate and reprogram from outside the patient’s body. Yet at bottom all pacemakers consist of two components: a pulse generator, which includes electronic circuitry and a power source, and a lead—one or more insulated wires connected to the pulse generator that terminate in an electrode, through which electrical current enters or leaves the heart.
Forty years ago, before Frank Henefelt had developed heart block, pacemakers looked completely different from the miniature implanted devices of today. At that time the term cardiac pacemaker referred to a large piece of electrical equipment that resuscitated people in the hospital. Medical electronics had not yet entered the transistor era, so the pulse generator of the mid-1950s was a plug-in device the size of an old tabletop radio. The leads were thick wires, and the electrodes were strapped to the patient’s chest.
Paul M. Zoll, a cardiologist at Beth Israel Hospital in Boston, had invented this external pacemaker in 1952. Hospital staffers could wheel in the pacemaker, plug it into the nearest electrical socket, and keep a patient alive through a severe Stokes-Adams attack in hopes that the heart would eventually carry on for itself. One hospital pacemaker could serve many patients.
Between 1957 and 1960 research physicians and engineers redefined and miniaturized ZoIPs original pacemaker. By using transistors, they were able to shrink the pulse generator to the size of a pocket watch. They unplugged it from the hospital’s electrical system and gave it a battery, encapsulated the circuitry in rubber, implanted the unit inside the patient’s body, and attached the pacing electrode to the outer wall of the heart itself.
As the hardware of pacing abruptly changed, the pacemaker’s therapeutic uses changed as well. Physicians began to think of the device as something that belonged not to the hospital but to the patient, who might carry it indefinitely. They redefined pacing as a therapy for chronic heart block, not just for the acute crisis of a Stokes-Adams attack.
Back in 1952 Zoll had demonstrated that it was possible to pace the heart safely and effectively for hours at a time. A few years later heart surgeons at the University of Minnesota’s medical school unintentionally assisted in the pacemaker’s transition from a hospital-bound piece of emergency equipment to a permanently implanted device. C. Walton Lillehei, a pioneer open-heart surgeon at Minnesota, began to stimulate the hearts of children whose conduction cells had been damaged during surgery to correct congenital heart defects. Heart block was appearing in about 10 percent of his surgical cases, and it was invariably fatal. Lillehei tried stimulating his patients’ heartbeats with drugs and had only limited success. He knew of ZoIPs cardiac pacemaker—but ZoIPs system, because it was entirely external, required fifty volts or more. Many adults could tolerate external pacing for only brief intervals, and Lillehei’s patients were children who needed continual pacing for up to three weeks as their conduction cells healed.
In 1957 Lillehei began to sew the bare tip of a Tefloncoated stainless-steel wire into the myocardium—the heart wall—during open-heart surgery. He would then bring the myocardial wire out through the surgical wound, connect it to an external pulse generator, and bury a second wire under the patient’s skin to complete an electrical circuit. Since the electrode made direct contact with the heart, instead of the outside of the chest, less than five volts was required for successful pacing. Weeks later, when the heart’s own conduction system had mended, the surgeon would gently tug on the myocardial wire and pull it from the child’s body. With this improvised procedure, Lillehei greatly reduced the postsurgical mortality rate for his patients.
Lillehei still relied on a large external pulse generator plugged into a wall socket. But he wanted his patients to be mobile, and for this, the electrical cord was a huge nuisance. “They wanted to wander around and get active,” Lillehei says. “They couldn’t go any farther than the cord. We had to string wires down the hall. And then, if they needed an X ray or something that couldn’t be done in the room, you couldn’t get on the elevator so you had to string them down the stairwells. It seemed that almost everything you wanted was on a different floor. We needed something battery-operated.’
He asked Earl Bakken, a young electrical engineer who repaired equipment for the department of surgery, to build a battery-powered external pulse generator that patients could carry with them. Early in 1958 Bakken presented Lillehei with a small device that ran on flashlight batteries. The patient could wear it in a belt holster or on a cord around the neck. Soon heart surgeons from around the country, many of whom had trained with Lillehei at Minnesota, began to order battery-powered pulse generators from Bakken’s tiny company, Medtronic.
Lillehei and his colleagues had thoroughly changed ZoIPs design and put the pacemaker to a new use. Ten years earlier the idea of connecting an electrical source to a wire inserted into the wall of the heart would have been inconceivable to the medical community. But by the late 1950s surgeons were developing a sense of confidence about working around the heart and even opening it. The pacemaker designed in Minneapolis was a child of the revolution in heart surgery as well as of the solidstate revolution.
THIS NEW VERSION of cardiac pacing had some puzzling problems, however. Surgeons were baffled to find that in the days following an operation, the pacemaker’s output had to be raised higher and higher or it would fail to stimulate the heart. They later discovered that scar tissue was forming around the tip of the pacing wire. Sometimes, too, the myocardial wire would break—and no wonder, for at sixty impulses per minute, the motion of the beating heart caused the wire to flex 86,400 times daily.
For Lillehei’s purposes, an external pulse generator with a myocardial wire was usually satisfactory, since he needed to pace his heart patients for only a few days. But by 1957 a number of research groups in the United States and Europe were beginning to think about pacing elderly people whose conduction systems were permanently impaired. In Boston Zoll had decided that resuscitating patients was just a stopgap: “After the initial excitement of saving the patient from the initial episode of standstill, everybody relaxes and you come back later … and find the patient had another episode. … You can resuscitate a patient … if you are ready all the time for the rest of the patient’s life, and that is a big order.” Zoll, the inventor of the external pacemaker, began to contemplate miniaturized pacemakers that would be fully implanted and would function for years.
Lillehei and others at Minnesota were thinking along the same lines. “When we saw how effective the wire and the pacemaker were, in these blocks that we were creating through surgery, we looked around and … started to realize that this thing must be much more common than the experts said. A lot of the sudden deaths … must have been Stokes-Adams, heart block. So we started treating some patients with heart block not associated with surgery.”
William M. Chardack, chief of thoracic surgery at the Veterans Administration hospital in Buffalo, and his colleague Wilson Greatbatch, an electrical engineer, were intrigued by Zoll’s and Lillehei’s reports. They canvassed heart specialists about the idea of permanent pacing but found that most considered heart block to be a rare condition. “Obviously, the disorder with its ominous prognosis had taken its toll well before the patient was referred to the specialist,” Chardack commented later. “Since no effective therapy was available, the level of diagnostic suspicion was low.” Lillehei had thought the same: Many people who could use a pacemaker died before being examined by a physician competent to diagnose heart block. Chardack “came away with the feeling that the need for a permanently implantable pacemaker was greater than it appeared to be.”
Working together, Chardack and Greatbatch invented and tested an implantable pacemaker. By the fall of 1959 they judged that it was ready to use with a human patient. (Surgeons at the Karolinska Institute in Stockholm had implanted a somewhat similar device in October 1958, but it failed after a few days, and they did not try again.)
In designing an implantable pulse generator, Greatbatch drew on numerous technologies of World War II and the Cold War. To create the electrical pulses, he employed a circuit developed at MIT’s famous wartime Radiation Laboratory. The hand-soldered circuitry contained two junction transistors among its eight components. For the battery he used ten tiny mercury-zinc cells that had been invented in 1947 for Army walkie-talkies. He tried to protect the assembly from shorting out because of seepage of bodily fluids by potting the cells and the circuitry in epoxy resin, the substance he had recently used to protect biomédical amplifiers that would monitor the vital signs of monkeys fired into space. On advice from an engineer at Medtronic, he encapsulated the pulse generator in a thin shell of DowCorning silicone rubber.
The problem that proved most difficult was finding a stable lead to get the stimulus to the heart. In their early trials using dogs, the Buffalo group relied on the technique developed at Minnesota: Open the chest and affix a Teflon-coated stainless-steel wire to the myocardium. They encountered the same problems with scar tissue that Lillehei and his associates had described. The group designed various new electrode structures, none of which proved effective for long. Eventually Chardack and Greatbatch adopted a new kind of lead invented at Medtronic. It resembled a tiny electrical plug—two stainless-steel pins mounted on a silicone platform—and it plugged directly into the wall of the heart. When connected to an external pulse generator, this design had proved effective in a few patients.
DURING THE 1950S LIFE-SUSTAINING DEVICES did not have to undergo the lengthy, rigorous clinical trials that are required today. After about a year of testing in the animal lab, Greatbatch recalled, “we had worked our [pacemaker] survival time up from four hours to four months and felt ready to start looking for a suitable patient.” In September 1959 Chardack implanted the new electrode in a sixty-five-year-old man and paced him for five weeks on the Greatbatch pulse generator, without implanting the generator. Two days before it was scheduled to go into his body, the patient unexpectedly died. Chardack later commented, “If the event had occurred two days following rather than before the [implantation], the patient’s demise no doubt would have raised all sorts of questions.” Chardack waited five months before finding a second suitable patient. On April 18, 1960, he implanted his pacemaker in another elderly man with complete heart block—Frank Henefelt, the former Fierce-Arrow inspector from Buffalo.
At first Chardack kept the pulse generator outside Henefelt’s body, as he had done with the earlier patient. On June 6, after it was clear that Henefelt had recovered his strength and was tolerating pacing well, Chardack implanted the generator in the left side of his abdomen. Henefelt made a normal recovery and lived for two and a half more years. A journalist wrote that he “raked the leaves in his yard last fall and can putter around the house or walk to the neighborhood stores. He has had no more fainting spells, and his wife says she is no longer on edge all the time for fear he’ll fall.”
Chardack and Greatbatch had already been in touch with Medtronic about using the company’s platform electrode. In October 1960 the two inventors signed a licensing agreement. Medtronic, which at the time had fewer than forty employees, would manufacture and distribute the pacemaker and successor models under the brand name Chardack-Greatbatch Implantable Cardiac Pacemaker. These devices remained the most widely used pacemakers in the world throughout the 1960s. Medtronic’s association with the two inventors propelled it to world leadership in the pacemaker industry, a position it still holds. Today the company has 12,000 employees. Its pacing division reported net sales of $1.5 billion in fiscal year 1996.
Since a run of pacing failures would surely doom the technology in the eyes of physicians, Chardack and Greatbatch emphasized safety above all else. The pacemaker’s unloaded output was roughly five to eight volts, several times what was necessary to stimulate the heart. “The objective was simply to drive the heart,” Greatbatch later wrote, “without much regard for economy of battery life” or other refinements.
AS OFTEN HAPPENS WITH A NEW MEDICAL device, the pacemaker was given its initial trials on patients close to death, men and women with such extreme symptoms that they severely tested the effectiveness of the device. Nearly all of Chardack’s first patients were experiencing frequent Stokes-Adams attacks, and seven of the first fifteen had had periods of complete unconsciousness lasting more than twenty-four hours. Most were unable to engage in the mildest forms of exercise.
Physicians who implanted pacemakers in these patients reported numerous serious failures that required new operations: broken or dislodged leads, premature battery depletion, leakage of body fluids into the pulse generator. Yet despite the problems, pacemakers proved effective at giving people months or years of life that they would not otherwise have enjoyed. Most of Chardack’s early patients were elderly (though two were children and one was a young adult). What particularly gratified Greatbatch was seeing how cardiac pacing could restore an elderly person’s mental alertness. “When in [heart] block, these people generally didn’t have enough blood supply to their brain. The kids would say, ‘Well, grandpa’s dottery.’ With a pacemaker, grandpa could snap back at the kids and be in the mainstream again.”
Implanting a pacemaker in the ChardackGreatbatch era meant putting the elderly patient under general anesthesia, opening the abdomen and the chest, placing an artificial device inside the body, and exposing the surface of the heart. Surgeons performed the procedure, which put sick, elderly patients under considerable stress.
TODAY DOCTORS WHO IMPLANT pacemakers almost never expose the patient’s heart. Instead, using local anesthesia, they make a small incision just below the left or right collarbone. They then cut into one of the prominent veins running across the upper chest toward the heart, either the cephalic or the subclavian vein. The pacing wire is contained within a venous catheter. While observing the process on a fluoroscope screen, the doctor advances the catheter down the venous system, through the right atrium of the heart, and into the right ventricle.
Once the lead is positioned securely against the wall of the ventricle and tested for its electrical characteristics, the physician plugs it into the pulse generator and buries the generator beneath the chest muscles at the site of the incision. An experienced implanter can carry out this procedure in forty-five minutes or less, though complex cases take longer. Tines at the tip of the lead hold it securely in position against the endocardium, the inner lining of the heart. Over a period of a week or two, fibrous tissue grows around the electrode and binds it tightly to the endocardium.
This transvenous path to the ventricle antedates the Chardack-Greatbatch implantable pacemaker. A twenty-six-year-old surgical resident in New York City first used a catheter lead in a human patient in 1958. At Montefiore Hospital in the Bronx, Seymour Furman was helping set up the openheart surgery program. One of the senior surgeons asked Furman to learn the Minnesota technique of pacing the heart through a wire connected to an external pulse generator. Using dogs, he set to work on this task.
Unlike most thoracic surgeons of that era, Furman was also learning cardiac catheterization. This is a procedure in which the physician—usually a cardiologist, not a surgeon—inserts a thin catheter into a vein and advances it into the heart. By the 1950s heart specialists had learned to push catheters through the right atrium and down into the right ventricle. Using the catheter, they were able to measure pressures within the heart and assess the pumping efficiency of the chambers. Catheterization contributed to improved diagnosis of heart problems, an important aspect of the revolution in cardiac care.
Furman saw a possible new use for the heart catheter. Why not try putting the pacing lead inside the ventricle instead of attaching it to the outside? He passed a copper wire down a polyethylene catheter and wrapped the exposed tip around a small piece of tinfoil to create a crude electrode. In March 1958 he inserted this primitive lead down the jugular vein of a dog into the right ventricle and attached the other end to an external pulse generator. With this setup Furman was able to capture the dog’s heartbeat and pace the animal artificially.
Furman soon discarded the copper wire and tinfoil in favor of a standard catheter that cardiologists employed to take electrical readings within the chambers of the heart. After pacing several dogs, he showed the new system to his seniors at Montefiore. One of them was the chief of cardiology, John B. Schwedel, a man who, according to Furman, “felt that new things should be tried.” As a cardiologist Schwedel was particularly receptive to the idea of a catheter lead. Furman recalls that Schwedel “grasped the importance of the technique instantly, became extremely excited, and assured me that a clinical trial was mandatory and that he would help me.” Schwedel also assured Furman that “he would bear responsibility for the disasters, if any, but that if the technique [proved] successful the credit would be mine.”
IN JULY 1958 FURMAN SUCCESSFULLY PACED AN ELDERLY man with heart block for two hours during colon surgery by inserting his catheter lead in the vein at the crook of the patient’s arm and threading it up the arm to the heart. The patient tolerated the surgery well but died a few weeks later following a second operation, during which no pacemaker was used. Furman recalls that Schwedel “by this time was beside himself with the possibilities here.” He called the catheter lead “a phenomenal technique” and said, “Push on. It’s yours.”
“Every doctor has one case,” an old saying reminds us—one astonishing case worth reporting to the profession. The story of Furman’s second patient, Pincus Shapiro, has become a classic in the medical lore on cardiac pacing. Shapiro was a severity-eight-year-old man, a private patient of Schwedel who suffered from chronic congestive heart failure. When Furman began on the case, in August 1958, Shapiro had developed heart block with occasional Stokes-Adams seizures. The team at Montefiore Hospital maintained him on a Zoll external pacemaker while they tried drug therapy to stimulate the heart, but his condition deteriorated, and he remained under sedation most of the time.
In mid-August 1958 Furman pushed the catheter from Shapiro’s left arm into his right ventricle and embedded the second electrode under the skin in his chest. The Zoll external pacemaker immediately achieved capture of the heartbeat. With a steadier heart rhythm, Shapiro gradually improved. In October he was allowed to sit in a chair in his hospital room. Soon he was reading and writing, and Furman decided to get him up and about. Furman put the external pulse generator on a hospital cart that Shapiro could push. He had a long extension cord made up so that his patient had “a range of almost 100 feet down the hospital corridor. We’d have cords at one outlet in the corridor, cords at another outlet. He’d walk the full extent of one cord, then Fd come by, the nurse would hold him tightly, and I’d switch plugs. Off he’d go again.”
Shapiro would remain an invalid for the rest of his life, but he was alert and responsive, his condition stabilized, and his heart appeared ready for the burden of sustaining its own rhythm. On November 18 Furman withdrew the catheter. The pacemaker had managed this patient’s heart, most of the time, for ninety-six days.
Furman’s technique required no surgical opening of the chest, certainly a great advantage in treating the sick, elderly patients who typically suffered from heart block. Furman and Schwedel emphasized that with an endocardial electrode it was not necessary to raise the voltage as the days passed. The case demonstrated “the maintenance of sensitivity of the endocardium to stimulation after many weeks of application of electric current.” Shapiro’s pacing threshold on day ninety-six remained what it had been on day one, just 1.5 volts.
THE STORY OF FURMAN’S SECOND CASE IS FAMOUS among pacemaker specialists because the transvenous approach it demonstrated has since become universal and because Furman later emerged as one of the most important figures in the field of cardiac pacing. He still implants pacemakers at Montefiore Medical Center and edits the medical journal PACE . He was honored with a lifetime achievement award at a recent meeting of the North American Society of Pacing and Electrophysiology. Yet when the case of “P.S.” was first described in print in 1959, it caused few ripples. No American manufacturer commercialized Furman’s invention until 1964, and the catheter lead did not come into general use in the United States until the late 1960s. In a fast-moving field like cardiac pacing, why did physicians neglect it for years?
Part of the reason is that Furman was young and unknown. He had his supporters, but the best-known pioneers of cardiac pacemaker work—Zoll, Lillehei, and Chardack—were initially unenthusiastic about endocardial pacing. Indeed, there were some problems with Furman’s method. Starting with his fifth patient, Furman began inserting the lead through the right external jugular vein at the base of the neck and attaching it to a battery-powered Medtronic external pulse generator. This was an important advance over inserting the lead at the elbow, but it still left the patient with a partly external pacing system. Many patients had multiple episodes of infection from bacteria that gained access to their bodies via the pacing lead. In addition, during the crucial years of 1960-64, when cardiacpacemaker implantation was gaining a foothold in American medicine, Furman was absent from Montefiore, first in military service and then on a residency year at Baylor University.
In contrast, the Chardack-Greatbatch system was available from the leading company, Medtronic, and William Chardack served as a vigorous champion of the invention. In presentations at medical conventions and published papers, he meticulously analyzed his case outcomes. Then in 1962 Medtronic introduced a new coiled-spring myocardial lead that Chardack had devised. It proved more reliable than the earlier platform lead, with stable electrical properties and much less breakage in the body. As surgeons gained experience with myocardial pacing, there seemed little reason to switch to a radically different technology.
Most important, inserting a catheter into the heart was a technique that cardiologists generally performed, while implantation of a pulse generator required the skills and credentials of a surgeon. The invention of the pacemaker had come as part of an advancing front in treatment for heart disease, and at the center of that front stood the heroic figure of the cardiothoracic surgeon. The field of pacing was the surgeon’s property, and surgeons felt comfortable with the myocardial lead.
In the early 1960s Furman’s invention began to win a small following, particularly in Sweden and Britain. A pacemaker manufacturer in Stockholm, Elema-Sch’f6nander, introduced a catheter lead in 1962. Around the same time, a handful of American surgeons began to use the catheter lead with an external pulse generator to maintain and strengthen the patient for a few days before performing a myocardial implant. This experience with temporary transvenous pacing helped acquaint surgeons with the virtues of the catheter lead.
BY 1965 GROWING REPORTS OF SUCCESSFUL long-term transvenous pacing in Sweden, the United States, and Britain had led Medtronic to introduce a transvenous catheter lead. Meanwhile, as manufacturers down-sized the pulse generator, surgeons began to implant it in the patient’s chest or side above the diaphragm. It then became possible to introduce the transvenous lead through a vein in the upper chest, connect the lead to the pulse generator, and bury the entire system. Statistical data also revealed that the transvenous procedure was less risky for patients. Hospital mortality rates ranged from O to 3 percent, considerably below the rates with myocardial implantation.
Enactment of the Medicare program in 1965 also encouraged transvenous pacing. Heart block chiefly afflicted older people, and now the federal government would be paying most of the cost of their health care. It is no surprise that as the number of potential patients grew, the number of physicians interested in pacemaker work began to grow too. By opening the field of pacing to cardiologists as well as surgeons, the transvenous catheter lead enabled the health-care system to keep up with the surge of patients suffering from disorders of the heartbeat. Today more than half the implanting physicians in the United States are specialists in cardiology.
Within a decade after the invention of the ChardackGreatbatch implantable pacemaker, physicians and manufacturers had settled on the main features of a standard pacemaker design. One thing had been obvious since the case of Frank Henefelt in 1960: The pacemaker would be a fully implanted, battery-powered device that would manage the heartbeat continuously and routinely. This meant that patients could leave the hospital and resume their normal daily routine with occasional visits to an outpatient clinic.
Twenty years earlier few doctors dreamed of long-term pacing for permanent heart block. The idea emerged only at the end of the 1950s. Even some of the leading inventors in the field, such as Lillehei and Furman, came to it after inventing their new pacing systems. Chardack’s implantable pacemaker opened up the medical practice of cardiac pacing, but its lead—essentially an insulated wire sewn down on the outside of the heart—proved a byway, not the main route of development. Furman’s catheter lead did not emerge out of clinical experience with myocardial pacing or as a reaction to it, but rather as a separate stream of inventive activity.
Physicians accepted the Chardack-Greatbatch method at first, then switched to Furman’s endocardial transvenous lead. The original myocardial pacing system of 1960 fitted poorly with broader developments in the field of pacing, especially the growing numbers of patients and the desire of nonsurgeons to implant pacemakers. The story of the cardiac pacemaker reminds us that the evolutionary path of a new invention often does not resemble a broad, wellmarked highway so much as a complex, branching road system with twists and turns, blind alleys, and more than one possible destination.
