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Since its invention more than 60 years ago, the heart pacemaker has improved the lives of millions of people, including the Canadian engineer who invented it.
It’s hard to believe that the invention of the pacemaker, which has helped millions worldwide, was unintentional. It came out of research into “cold heart surgery” in the 1940s by Canadian surgeons Dr. Wilfred G. Bigelow and Dr. John C. Callaghan at the Banting Institute in Toronto.
John Hopps, the Canadian engineer who built the first pacemaker, is considered the father of bioengineering. In 1984, Hopps received a pacemaker himself, as did Dr. Wilfred Bigelow many years later.
Dr. Bigelow believed that the only way cardiovascular medicine could advance was by enabling open-heart surgery. Based on his experience as a field medic during World War II, he was convinced that cooling the body and slowing the heart rate was the way to go.
One of the challenges the two surgeons faced was keeping the heart beating while the body was hypothermic. During an experimental surgery on a dog, they noticed that stimulating a stopped heart with an electrical probe could restart it, and that sending pulses of electrical current could actually change the heart’s rate. It was “a tremendous bit of good fortune,” said Dr. Bigelow in an interview about the discovery with the Canadian Medical Hall of Fame.
To turn this discovery into a clinical device, they recruited John Hopps, an electrical engineer from the National Research Council of Canada.
From vacuum tubes to transistors
The first pacemaker, built by Hopps in 1949, was a bulky device that used vacuum tubes to generate electrical pulses. An insulated wire inserted through the jugular vein delivered the electric shocks to the right atrium of the heart. These shocks provided the artificial pacing.
It would be another 10 years before developments in technology would make the implantable pacemaker a reality. The critical turning point was the introduction of small silicon transistors to replace vacuum tubes. This technology allowed pacemakers to become small enough to be implanted in the body.
The first recipient of an implantable pacemaker was Arne Larsson in 1958. The prototype was about the size of a tin of shoe polish. It was built in the kitchen of Dr. Rune Elmqvist, and implanted by Dr. Åke Senning, a cardiac surgeon at Karolinska University Hospital in Solna, Sweden. The device lasted three hours. Over his lifetime, Mr. Larsson received 28 devices and lived to the age of 86.
The pacemaker designed by Dr. Elmqvist required regular recharging. Doctors were concerned that patients would forget to recharge their pacemaker, or find the process difficult. The next generation of devices was made with mercury-zinc batteries, which were designed to last up to five years. However, most failed within two years.
Pacemakers go atomic
In 1970, the first nuclear-powered pacemaker was implanted into a patient in France. (The first in Canada was implanted in 1973.) Designed to last at least 10 years, it resembled a 35-mm film canister and used the isotope plutonium-238, which was encased in three layers of metal to protect the patient from radioactivity.
Eventually, modern lithium-ion batteries replaced the plutonium ones. Lithium-ion batteries are still used to power pacemakers today.
The modern pacemaker
Today’s pacemakers are about the size of a USB stick. Pacemaker surgery is usually performed in less than an hour under a local anesthetic. Most people return to normal activities within a few days.
An early experiment
The first record of an electrical current being used to stimulate the heart was in 1889. The Scottish physiologist John Alexander MacWilliam discovered that he could start and control the heartbeat of a cat by applying periodic electric shocks through needle electrodes inserted in the heart.
In addition to being smaller, modern pacemakers are far more complex. Programmable pacemakers were introduced in the 1970s that allowed doctors to choose different pulse speeds and durations.
Modern pacemakers include microprocessors that collect data about how well the heart and pacemaker are working. These microprocessors can also monitor the patient’s physical activity and adjust the heartbeat as needed. As well, pacemakers can now regulate and synchronize contractions between the multiple chambers of the heart. These dual-chamber models help the heart beat more efficiently and can reduce the symptoms of heart failure.
Some pacemakers can even restart the heart if it stops. However, since these implantable cardioverter defibrillators (ICDs) must be able to deliver a large zap of electricity, they have fairly powerful batteries and are more bulky — about the size of a hockey puck.
Looking to the future
One of the biggest risks for patients with pacemakers is deterioration of the wires, called leads, that connect the pacemaker to the heart. Because the wires heal into the heart and create scar tissue, removing defective ones can be tricky.
One solution being investigated is a wireless cardiac stimulation device. Instead of electrical currents, this pacemaker uses ultrasound to stimulate a receiver (about the size of a grain of rice) that has been placed on the heart.
Another possibility involves using magnetic fields to stimulate a receiver placed on the heart. Even more futuristic are biological replacements for mechanical pacemakers, such as those based on gene and stem cell technology. The hope is that these “biological pacemakers” could reduce dependence on external pacemakers, and perhaps one day eliminate them altogether.