Cynaburst
03-14-2009, 12:30 AM
http://www.economist.com/science/tq/displaystory.cfm?story_id=13174305
Case history
The rhythm of life
Mar 5th 2009
From The Economist print edition
Medical technology: Devices that maintain and restore a normal heartbeat date back to the 1950s. Now they are becoming far more widely used
In 1889 John Alexander MacWilliam, a brilliant young Scottish physiologist, made a shocking discovery. Using little more than a metronome and a needle electrode inserted into the hearts of cats, he found that he could speed up and restore normal heart rhythms by applying periodic electrical shocks. His findings led to the artificial pacemaker and, in the 1980s, the implantable defibrillator, spawning the multibillion dollar “heart-rhythm management” industry.
In the half-century after the first pacemaker was implanted, the principles behind the technology changed very little from MacWilliam’s first demonstration. But the industry is now undergoing a technological revolution. A new generation of smaller, smarter devices promises to administer fewer unnecessary shocks and to reduce the size of the characteristic bulge in patients’ chests. As the technology improves and the list of treatable conditions grows, larger numbers of ever-younger patients are being fitted with these devices. More than half a million pacemakers and defibrillators are now implanted each year, each of which will see out its battery life supervising and regulating tens of millions of heartbeats.
The first patient to receive a fully implantable artificial pacemaker was a 43-year-old Swede called Arne Larsson. He had his wife, Else-Marie, to thank for it. Not willing to accept her husband’s seemingly inevitable death from a heart condition, she decided that he might benefit from the kind of cardiac pacing that she had heard was being tested on animals. Using her formidable powers of persuasion she convinced Ake Senning, a surgeon at the Karolinska University Hospital in Stockholm, and Rune Elmqvist, a medically trained engineer, to build a device especially for her husband.
The first prototype was constructed in Dr Elmqvist’s kitchen and was implanted in Mr Larsson on October 8th 1958. It lasted just three hours. The next morning Mr Larsson received a second, identical device that lasted two days. Undeterred, he went on to receive 26 further devices. Mr Larsson became a prominent campaigner for the technology until his death at the age of 85—from causes unrelated to his heart condition.
Electrical pulses
An artificial pacemaker works by restoring the function of a faulty sinoatrial node, the heart’s natural pacemaker. Normally the sinoatrial node generates regular electrical pulses that spread across the chambers of the heart, causing the cells to contract in synchrony. When the sinoatrial node starts to malfunction it can cause dangerously slow or erratic rhythms to develop. By inserting electrodes into one or more of the chambers of the heart, via a large vein, it is possible to mimic its function by applying small electrical shocks at regular intervals. Power leads link the electrodes to a small hermetically sealed metal box, called the generator, that contains the battery and electronics.
Today’s generators are not much bigger than a matchbox. Mr Larsson’s first devices were the size of a tin of shoe polish. Indeed, that is precisely what Dr Elmqvist used to create moulds for his epoxy-resin generators. But most of the pacemakers that followed were considerably larger. The reason was, quite simply, power. Dr Elmqvist was able to make his devices relatively small because they were designed to be recharged regularly from outside the body, using an induction loop. As other pacemakers were developed, this approach was quickly deemed imprudent. Because patients tended to be elderly, cardiologists were concerned that they would find the recharging process difficult, or might forget to do it, says David Steinhaus, medical director of Medtronic—one of the three companies, along with Boston Scientific and St Jude, that dominate the field.
Switching to non-rechargeable designs meant that generators needed enough power to run for years at a time. This meant using big mercury-zinc batteries, making the generators up to five times bigger than modern devices. Unfortunately the batteries also gave off hydrogen gas as a chemical by-product, which diffused into the body. This was less than ideal. But Arjun Sharma, chief patient-safety officer at Boston Scientific, points out that at the time it was the best technology available. Despite these drawbacks, the first implantable pacemakers were an improvement over what had come before. Before Mr Larsson received his implantable device, patients had received pacing from huge external devices. “These were the size of car batteries,” says Dr Sharma. “They were so big they were having to roll them around on carts.”
Before the first implantable device, pacemakers were so big they were pushed around on trolleys.In the mid-1960s the search for better power supplies prompted a company called Nuclear Materials and Equipment Corporation in Apollo, Pennsylvania, to take the radical step of developing an atomic pacemaker. Powered by a tiny piece of radioactive plutonium-238, the device was designed to last ten years—five times longer than mercury-zinc batteries. To protect the patient, the battery was sealed in three layers of casing designed to withstand a rifle shot. The first radioactive pacemaker was put into a patient in France in 1970.
The lifespan of these devices was a lot longer than that of their predecessors. Sometimes they even outlasted their patients, says Dr Steinhaus. (“I took one out that had been in for 19 years,” says Dr Sharma.) But there were problems beyond the risk of radiation poisoning to the patient. Removed devices were, by definition, nuclear waste and had to be disposed of accordingly. Eventually the new lithium-iodine battery offered a radiation-free eight-to-ten year lifespan, and no exhaust gases to worry about.
Improved batteries also led to a beefed-up version of a pacemaker that could restart the heart, and correct irregular or dangerously fast heartbeats, when necessary. These devices, known also as implantable cardioverter defibrillators (ICDs), work by zapping the heart with a large jolt of electricity. The first ICD was implanted in 1980 at Johns Hopkins Hospital by Levi Watkins, after more than 20 years' work by a pioneering team at Sinai Hospital, in Baltimore.
ICDs are considerably more advanced and complex than pacemakers and use small computers to sense electrical activity, monitor the heart and determine when and how to apply a therapeutic shock. The latest models are equipped with remote-telemetry features that allow doctors to monitor their operation. After a series of trials they have been found to be more effective at preventing some forms of sudden cardiac death than drug treatments are. As a result, they have become popular in recent years, and implantation has become a routine outpatient procedure that can take less than 30 minutes.
The life-saving benefits of this technology are irrefutable. But some cardiologists think there is still plenty of room for improvement. One of the problems is with the power leads, which can fail for a variety of reasons. Manufacturing problems have resulted in large-scale recalls in some cases, and the leads can develop faults while within the body due to the mechanical stresses caused by movement or impact. According to Andrew Grace, a cardiologist at the Papworth Hospital in Cambridge, Britain, patients with ICDs have a 20% chance of lead failure within ten years.
Modern devices are often able to detect the early signs of lead failure, so the patient is not in danger. The trouble is that replacing leads is itself risky. The ends of leads are barbed to encourage them to stay in place within the heart, so removing them can be tricky. If they fail to come out with a simple tug, which happens in about one in every 50 cases, then the only option is open heart surgery. Lead replacements have a morbidity rate of 2-5%, says Warren Smith at the Auckland City Hospital and Green Lane Hospital in New Zealand. (Replacing the generator, by contrast, is relatively straightforward, involving a small incision in the chest, and carries only a 1% risk of complications.)
This has led to several efforts to look for new ways to pace and defibrillate the heart. The one closest to market is a device developed by Cameron Health, a company based in San Clemente, California, called the “subcutaneous ICD” or S-ICD. It works like a normal ICD but has a crucial difference: instead of placing the electrodes inside the heart and threading the power leads along veins, the electrodes and leads sit outside the heart, just under the patient’s skin. This should make the device easier and safer to implant. “Historically, lead-related problems have presented some of the most significant challenges to clinicians,” says Jay Warren, the boss of Cameron Health.
Case history
The rhythm of life
Mar 5th 2009
From The Economist print edition
Medical technology: Devices that maintain and restore a normal heartbeat date back to the 1950s. Now they are becoming far more widely used
In 1889 John Alexander MacWilliam, a brilliant young Scottish physiologist, made a shocking discovery. Using little more than a metronome and a needle electrode inserted into the hearts of cats, he found that he could speed up and restore normal heart rhythms by applying periodic electrical shocks. His findings led to the artificial pacemaker and, in the 1980s, the implantable defibrillator, spawning the multibillion dollar “heart-rhythm management” industry.
In the half-century after the first pacemaker was implanted, the principles behind the technology changed very little from MacWilliam’s first demonstration. But the industry is now undergoing a technological revolution. A new generation of smaller, smarter devices promises to administer fewer unnecessary shocks and to reduce the size of the characteristic bulge in patients’ chests. As the technology improves and the list of treatable conditions grows, larger numbers of ever-younger patients are being fitted with these devices. More than half a million pacemakers and defibrillators are now implanted each year, each of which will see out its battery life supervising and regulating tens of millions of heartbeats.
The first patient to receive a fully implantable artificial pacemaker was a 43-year-old Swede called Arne Larsson. He had his wife, Else-Marie, to thank for it. Not willing to accept her husband’s seemingly inevitable death from a heart condition, she decided that he might benefit from the kind of cardiac pacing that she had heard was being tested on animals. Using her formidable powers of persuasion she convinced Ake Senning, a surgeon at the Karolinska University Hospital in Stockholm, and Rune Elmqvist, a medically trained engineer, to build a device especially for her husband.
The first prototype was constructed in Dr Elmqvist’s kitchen and was implanted in Mr Larsson on October 8th 1958. It lasted just three hours. The next morning Mr Larsson received a second, identical device that lasted two days. Undeterred, he went on to receive 26 further devices. Mr Larsson became a prominent campaigner for the technology until his death at the age of 85—from causes unrelated to his heart condition.
Electrical pulses
An artificial pacemaker works by restoring the function of a faulty sinoatrial node, the heart’s natural pacemaker. Normally the sinoatrial node generates regular electrical pulses that spread across the chambers of the heart, causing the cells to contract in synchrony. When the sinoatrial node starts to malfunction it can cause dangerously slow or erratic rhythms to develop. By inserting electrodes into one or more of the chambers of the heart, via a large vein, it is possible to mimic its function by applying small electrical shocks at regular intervals. Power leads link the electrodes to a small hermetically sealed metal box, called the generator, that contains the battery and electronics.
Today’s generators are not much bigger than a matchbox. Mr Larsson’s first devices were the size of a tin of shoe polish. Indeed, that is precisely what Dr Elmqvist used to create moulds for his epoxy-resin generators. But most of the pacemakers that followed were considerably larger. The reason was, quite simply, power. Dr Elmqvist was able to make his devices relatively small because they were designed to be recharged regularly from outside the body, using an induction loop. As other pacemakers were developed, this approach was quickly deemed imprudent. Because patients tended to be elderly, cardiologists were concerned that they would find the recharging process difficult, or might forget to do it, says David Steinhaus, medical director of Medtronic—one of the three companies, along with Boston Scientific and St Jude, that dominate the field.
Switching to non-rechargeable designs meant that generators needed enough power to run for years at a time. This meant using big mercury-zinc batteries, making the generators up to five times bigger than modern devices. Unfortunately the batteries also gave off hydrogen gas as a chemical by-product, which diffused into the body. This was less than ideal. But Arjun Sharma, chief patient-safety officer at Boston Scientific, points out that at the time it was the best technology available. Despite these drawbacks, the first implantable pacemakers were an improvement over what had come before. Before Mr Larsson received his implantable device, patients had received pacing from huge external devices. “These were the size of car batteries,” says Dr Sharma. “They were so big they were having to roll them around on carts.”
Before the first implantable device, pacemakers were so big they were pushed around on trolleys.In the mid-1960s the search for better power supplies prompted a company called Nuclear Materials and Equipment Corporation in Apollo, Pennsylvania, to take the radical step of developing an atomic pacemaker. Powered by a tiny piece of radioactive plutonium-238, the device was designed to last ten years—five times longer than mercury-zinc batteries. To protect the patient, the battery was sealed in three layers of casing designed to withstand a rifle shot. The first radioactive pacemaker was put into a patient in France in 1970.
The lifespan of these devices was a lot longer than that of their predecessors. Sometimes they even outlasted their patients, says Dr Steinhaus. (“I took one out that had been in for 19 years,” says Dr Sharma.) But there were problems beyond the risk of radiation poisoning to the patient. Removed devices were, by definition, nuclear waste and had to be disposed of accordingly. Eventually the new lithium-iodine battery offered a radiation-free eight-to-ten year lifespan, and no exhaust gases to worry about.
Improved batteries also led to a beefed-up version of a pacemaker that could restart the heart, and correct irregular or dangerously fast heartbeats, when necessary. These devices, known also as implantable cardioverter defibrillators (ICDs), work by zapping the heart with a large jolt of electricity. The first ICD was implanted in 1980 at Johns Hopkins Hospital by Levi Watkins, after more than 20 years' work by a pioneering team at Sinai Hospital, in Baltimore.
ICDs are considerably more advanced and complex than pacemakers and use small computers to sense electrical activity, monitor the heart and determine when and how to apply a therapeutic shock. The latest models are equipped with remote-telemetry features that allow doctors to monitor their operation. After a series of trials they have been found to be more effective at preventing some forms of sudden cardiac death than drug treatments are. As a result, they have become popular in recent years, and implantation has become a routine outpatient procedure that can take less than 30 minutes.
The life-saving benefits of this technology are irrefutable. But some cardiologists think there is still plenty of room for improvement. One of the problems is with the power leads, which can fail for a variety of reasons. Manufacturing problems have resulted in large-scale recalls in some cases, and the leads can develop faults while within the body due to the mechanical stresses caused by movement or impact. According to Andrew Grace, a cardiologist at the Papworth Hospital in Cambridge, Britain, patients with ICDs have a 20% chance of lead failure within ten years.
Modern devices are often able to detect the early signs of lead failure, so the patient is not in danger. The trouble is that replacing leads is itself risky. The ends of leads are barbed to encourage them to stay in place within the heart, so removing them can be tricky. If they fail to come out with a simple tug, which happens in about one in every 50 cases, then the only option is open heart surgery. Lead replacements have a morbidity rate of 2-5%, says Warren Smith at the Auckland City Hospital and Green Lane Hospital in New Zealand. (Replacing the generator, by contrast, is relatively straightforward, involving a small incision in the chest, and carries only a 1% risk of complications.)
This has led to several efforts to look for new ways to pace and defibrillate the heart. The one closest to market is a device developed by Cameron Health, a company based in San Clemente, California, called the “subcutaneous ICD” or S-ICD. It works like a normal ICD but has a crucial difference: instead of placing the electrodes inside the heart and threading the power leads along veins, the electrodes and leads sit outside the heart, just under the patient’s skin. This should make the device easier and safer to implant. “Historically, lead-related problems have presented some of the most significant challenges to clinicians,” says Jay Warren, the boss of Cameron Health.