Electricity Regulating Heartbeat:
The Pacemaker

Beth Israel Deaconess Medical Center 1952


Beth Israel Hospital's Dr. Paul Zoll forever changed medicine when he announced in 1952 that he had successfully used electrical stimulation to restart a patient's heart. A Boston native, Dr. Zoll's began at Harvard Medical School in 1932, which was followed by an internship at Beth Israel Hospital in Boston and a one-year residency in New York City. In 1939, Zoll returned to Boston as a junior member of a research group at Beth Israel.

When World War II broke out, Zoll was assigned to the 160th U.S. Army Station Hospital in England, where he was the cardiologist on Dr. Dwight Harken's surgical team. He assisted Dr. Harken in removing foreign bodies from the heart, and Zoll was struck by the irritability of the heart during these surgeries. He stated: "You just touch it and it gives you a run of extra beats-so why should the heart, that is so sensitive to any kind of manipulation, die because there's nothing to stimulate the chest? It wasn't sensible." Zoll's observations during World War II paved the way for his later discoveries.

Upon returning to Boston in 1945, Zoll resumed his research at Beth Israel and also entered the private practice. In the late 1940s, Dr. Zoll treated one of his private patients, a 60 year old woman, who had Stokes-Adams disease . She died three weeks after her first attack. Zoll was very frustrated because he believed her death was preventable, if only there was a method to stimulate the heart from standstill. This patient's death focused Dr. Zoll's attention on finding such a method.

Dr. Zoll was familiar with earlier work that showed the successful electrical stimulation of the heart in both rabbits and dogs. Thus, Zoll acquired a standard stimulator and set to work testing his ideas on dogs. Zoll realized that his pacemaker would have to stimulate the ventricles directly, unlike the earlier machines, which only stimulated the atria. After two years of testing his pacemaker in the laboratory, Dr. Zoll was able to resuscitate dogs whose hearts had been stopped for several minutes. The next step was testing his machine in humans.

In 1952, Zoll restarted the hearts of two patients. The first patient lived for 20 minutes, and the second one for 11 months. Zoll reported his results in the New England Journal of Medicine, and the reaction was celebratory by most. An electrical device had never before regulated a human heartbeat. However, Zoll did have some critics who believed his machine went against God's will. Zoll continued working on his model of the pacemaker, striving for a smaller and more portable device. Between 1960 and 1964, Zoll and his colleagues developed an implanted pacemaker.

However, the pacemaker had a limited applicability-it was able to save the lives of those with cardiac standstill or a slow heart rhythm, but it was not effective in reversing ventricular fibrillation. In his 1952 paper, Zoll suggested that is should be possible to disrupt ventricular fibrillation and stop cardiac arrest by applying an external electric countershock. In 1956, Zoll performed the first successful external cardiac defibrillation in a human. Today, cardiac defibrillators are found in every hospital, ambulance, and even commercial airlines.

Yet if these new techniques were to be successful, doctors needed a way to promptly recognize cardiac arrest in a hospitalized patient. Thus, in the early 1950s, Zoll and his technical collaborators developed cardiac monitors, which recorded each heart beat with an audible sign and sounded an alarm upon the start of cardiac arrest.

Dr. Zoll's research and inventions have saved millions of lives throughout the years, and the cardiac pacemaker, cardiac defibrillator, and cardiac monitor, all inventions of Dr. Zoll, are still three of the most important tools of cardiologists.