At the Heart of the Invention: The development of the Holter Monitor


You probably know someone with a heart condition, someone who had a heart attack or even heart surgery. I know I do. According to the Centers for Disease Control, heart disease is the leading cause of death for both men and women in the United States and the most common type of heart disease is coronary artery disease (CAD), which can lead to a heart attack. Sobering data.

There are ways to prevent heart disease such as embracing a healthy lifestyle and there are diagnostic tools to monitor our hearts too, thanks to the work of two creative and persistent men, Norman “Jeff” Holter (1914-1983) and Bruce Del Mar (b. 1913-).

Norman "Jeff" Holter

Their collaboration, which spanned two decades, produced a commercially viable heart monitor known as the Holter Monitor Test. The Holter Monitor is a portable device for continuously monitoring heart activity for an extended period of time, typically 24 hours. The monitor records electrical signals from the heart that are sent via a series of electrodes attached to the chest. The data is then analyzed for different sorts of heart beats and rhythms.

Heart monitor
Model 445 Mini-Holter Recorder, illustration from a brochure, 1976

Norman “Jeff” Holter, a native of Helena, Montana, was a biophysicist and inventor whose interests were not confined solely to physics. Holter’s interest in studying electrical activity in humans during their daily activities without touching them spawned his lifelong pursuit to develop the Holter Monitor. Holter’s goal was to radio broadcast and record the more obvious electrophysiological phenomena occurring in humans while carrying on their normal activities, rather than having them be inactive.

Patient attached to heart monitoring equipment: slide of a cartoon, undated

Holter’s first broadcast of a radioelectrocardiogram (RECG) took place circa 1947 and required 80 to 85 pounds of equipment, which Holter wore on his back while riding a stationary bicycle. Holter noted in 1982 that “The 85 lb. RECG, while not practical, represented a major breakthrough since before that time a patient had to lie quietly. Our greatest contribution was a radical one and was the beginning of an era where one could take ECG’s on skiers, parachute jumpers, runners, and just about any other type of vigorous physical activity.”

Advertisement for Del Mar Engineering Laboratories, 1965

Holter’s other contribution was to bring the overall size down to less than cigarette package size to be worn inside a man’s jacket handkerchief pocket. With the development of transistors, radioelectrocardiography was made obsolete and it became possible for all of the components to be placed in a single unit small enough for a coat pocket or purse. Holter was issued US Patent 3,215,136 on November 2, 1965, for the Electrocardiographic Means, and The Holter Research Foundation ultimately sold exclusive rights to the patent to Del Mar Engineering Laboratories, who became the acknowledged leader in Holter monitoring technology for over 40 years.

As articles describing the foundation’s invention of these devices began to appear in the professional literature, there was considerable demand from doctors and hospitals for the equipment. Holter was seeking a partner to manufacture his monitor, and finally met a suitable candidate in Bruce Del Mar in 1962.

Bruce Del Mar’s role as an innovator and collaborator with Holter is especially important because his work spurred the development of an entire diagnostic industry. The Del Mar Avionics Holter Monitor Records, 1951-2011, held at the Archives Center, document through correspondence, engineering notebooks, operator’s manuals more than just the invention of a heart monitor. The records reflect the successful collaboration of an independent inventor and a manufacturing firm to problem-solve, develop a solution, and bring to market a diagnostic technology.

Del mar
Bruce Del Mar

Del Mar wrote in February of 1965, ”We have continually improved circuitry and mechanical details to obtain greater service fidelity, accuracy, response, and reliability. The instruments we are now delivering are performing very well in the field. We should, however, be thinking and actively working ahead on new model improvements for 1966. Can I have your suggestions in this respect? That would be very much appreciated.” The correspondence reveals a deep level of commitment and investment from both parties to work out technical details, successfully market the monitor, and in general keep the project moving forward.

The successful collaboration between the two men would prove to be invaluable for countless numbers of people. To learn more about the Holter Monitor story, see the collection finding aid at the Archives Center’s web site.

Alison Oswald is an archivist with the Lemelson Center and Archives Center at the National Museum of American History. This post originally appeared on the Smithsonian Collections blog.