The interesting aspect of this project is that it is what is called a "spin-off" from the research in hypothermia.
You asked me to describe research that led to the development of the electrical cardiac pacemaker. The interesting aspect of this project is that it is what is called a "spin-off" from the research in hypothermia.
Our Banting Institute research team had no particular interest in the pacemaker mechanism of the heart. However, during one hypothermia experiment a dog had been anaesthetized, cooled to about a temperature of 22° centigrade, and the heart surgically exposed to study its reaction to cold. The heart unaccountably stopped. In a reaction of frustration the heart was poked with a probe. Lo and behold this produced a strong heart contraction. Poking it regularly produced a normal blood pressure. We quickly substituted an electrode with a mild electric shock with the same results.
Subsequent experiments were disappointing. Electrically stimulating the heart did not improve or increase the safety of hypothermia. But why not, as a separate project, explore the stimulation of the heart at normal body temperature.
I contacted Dr. Ballard of the National Research Council in Ottawa and asked him for bioengineering help with this and other projects in the laboratory. He kindly assigned a brilliant young electrical engineer, John C. Hopps, who would come from Ottawa to work with us for two or three days, then return to his specialized laboratory at the National Research Council with all the refinements in electronics of 1948.
The project was to create a repetitive electrical impulse that did not injure the heart muscle, and most closely resembled the impulse that travels down the special nerves of the heart from the body's natural pacemaker – a three millimetre node lying in the right atrium.
After extensive study, Hopps finally developed an electrical pacemaker circuit that would supply this type of gentle stimulation neatly encased in a metal cabinet 10x8x6 inches. The rate of stimulation was controlled by a dial.
The first problem we encountered was the difficulty in stopping a heart from beating at normal body temperature. With this solved, the ensuing experiments were conducted principally by Dr. John C. Callaghan, research fellow, and John C. Hopps and surgical assistants Donald Hughes and Kenneth Burley.
After reviewing the literature, we were amazed to discover that only one purposeful pacemaker had ever been developed, by Dr. A.S. Hyman of New York in 1932. It was a large contraption with a crank. When this was wound up, it would produce an intermittent electrical discharge of unknown current for 8 minutes through an electrode. He reported experiments with asphyxiated hearts of guinea pigs with no statistics. So 18 years later, the field was obviously still wide open.
The results of these experiments were exciting. They were recorded statistically and by motion pictures. The report by Dr. Callaghan and myself was presented to the American College of Surgeons in 1951.
This Canadian discovery demonstrated that:
- The pacemaker produced controlled rate heartbeats in a stopped heart.
- It dominated the natural pacemaker when applied to a normal beating heart and it was possible by turning a dial, to increase or decrease the rate of the heart (never before observed).
- A long cardiac catheter containing two electrode wires (bipolar stimulation) could be passed down a vein in the neck muscle into the heart. This allowed stimulation of the heart muscle without surgically exposing the heart (the current technique).
The report to the American College of Surgeons was dramatic and newsworthy. There was no discussion. Newspapers in the U.S. and Canada carried large headlines with outlandish claims of its potential use.
The original research was financed by a grant from the Defence Research Board and the National Research Council of Canada. More recent research has been supported by Medtronics of Canada. This original pacemaker console was too large to carry about, although several American universities ordered copies of the model for hospital use. P. Zoll and W. Lillehei in the U.S. reported successful use of the pacemaker in a small number of hospital patients. Because of its size it was of limited value.
For eight years, the pacemaker literally sat on the shelf until aeronautical research perfected transistor circuitry. This breakthrough allowed construction of a similar pacemaker so small that it could be implanted under the skin. Dr. Ake Senning of Stockholm was the first to accomplish this in 1959, eight years after our original report.
The evolution of the small, implantable modern pacemaker is unique in the annals of medical technology. It is a story of remarkable collaboration from the beginning between medicine and bioengineering with increasing sophistication in performance and increased battery durability. J.A. Hopps, the designer, is regarded as the father of bioengineering in Canada and remains active with his own pacemaker.
In Canada in 1989, there were 7,500 new pacemakers implanted into patients and 1,200 had their old battery pack replaced. There is a huge number of persons in Canada who have received pacemakers in the last thirty years. The total number is not known. In terms of health benefit it has been lifesaving and the recipients have been restored to an active productive life with freedom from fear.
*Deceased March 27, 2005