A History Of Pacemakers

The history behind the artificial pacemaker stretches back over 300 years. As a critical component of numerous scientific developments in medicine, specifically within cardiology, the pacemaker and its history have provided a foundation for basic electrophysiology, applied electrotherapy and various treatment technologies devoted to reducing both the mortality and morbidity of many diseases.

Connecting Electricity and Treatment

By the end of the 18^th century, publications by researchers like Luigi Galvani supported the consensus that electricity had powerful effects on organ tissues, specifically the heart. Galvani came to this conclusion after performing numerous frog experiments that demonstrated the electrical phenomenon that exists within the muscles and hearts of this organism. By making this connection between electricity and the heart, modern cardiac electrophysiology emerged.

Figure 1. Basic functional mechanisms to the Hyman pacemaker.

Introduction of the First Pacemaker

Dr. Albert Hyman engineered the first artificial pacemaker explicitly designed for cardiac purposes in 1932. Hyman’s device was designed to have a spring motor that was used to turn a magneto-generator and generate a source of electricity. Three centrifugal weights controlled the speed of the spring motor. The passing current would make intermittent contact with a series of rotating conductive surfaces. A neon lamp was also incorporated into the device to provide a light signal in response to when an electrical surge passed through the needle assembly to the heart.

To connect this type of pacemaker to the patient’s heart, a wire would be attached to the needle assembly that was plunged through the patient’s chest wall to provide access to a vein of the heart. The wire would carry the electrical impulse to the heart to help maintain a regular heartbeat. The spring motor was also responsible for propelling the interrupter disc; which was a mechanism involved in providing a voltage to the needle assembly electrode. The movement of the interrupter disc would subsequently stimulate a response of the right atrium. This disc was comprised of four conductors and an electrical insulator, each of which worked in conjunction with one another to generate an electrical impulse.

Unfortunately, as is true with any new invention, Hyman faced several problems as a result of the design of this pacemaker device. For example, the main issue of Hyman’s device involved the need to directly insert a needle into the right atrium of the patient’s heart, since this type of puncture would cause serious injury to the patient. A second limitation of Hyman’s pacemaker was the inability of the device to distinguish between fibrillation and defibrillation of the ventricles. Hyman’s pacemaker also exhibited a lack of efficacy concerning its low-voltage output of the electrical pulses generated.

In conclusion, the idea of a needle assembly connecting the heart to an external power pack was deemed an unsafe and ineffective measure to control rhythmic electrical stimulus to the heart muscles. Furthermore, since the action of the pacemaker excessively drained the power source of the pulse generator, it often caused the patient to experienced cardiac arrhythmias and even death.

Image Credits: Richman Photo/shutterstock.com

The First Implantable Pacemakers

Since Hyman, pacemaker technology has dramatically evolved to correct the limitations of his original device to develop a more practical and less painful implantable pacemaker. The first attempts to create an implantable pacemaker occurred in 1958 in Sweden by Ake Senning and Rune Elmqvist. In their design, silicon transistors were used to generate a pulse within a device that was small enough to be placed in the epigastrium under the skin. Arne Larsson, a 43-year-old man, was the first patient to have this device implanted. Since a nickel-cadmium battery powered this early pacemaker device, it had a limited lifespan. By the end of Larsson’s life at 86 years old, he had received a total of 26 different pacemakers.

In 1960, American scientist Wilson Greatbatch and cardiologist William Chardack developed a novel implantable pacemaker device that was instead powered by zinc-mercuric oxide battery cells. The lithium battery was encapsulated in epoxy to provide a 17-year long battery life, which significantly improved the longevity of the implantable pacemaker as compared to Senning and Elmqvist’s device. Figure 2 illustrates a surgical procedure whereby a pacemaker is inserted into the patient’s heart.

Greatbatch’s implantable pacemaker was designed to treat patients diagnosed with complete atria-ventricular heart block. The pacemaker circuit was designed to generate an electrical impulse with a repetition rate of 60 beats per minute, which mimicked the natural rhythmical heartbeat that typically ranges between 60 and 100 beats per minute. Their cardiac pacemaker was comprised of a blocking oscillator that created an electrical wave, whereas the transistor to the blocking oscillator is used throughout the pulse sent to the heart muscles. During the time in which a pulse is generated, a voltage is applied to switch on the oscillator, which then allows the pulse to make contact with the transistor and ultimately increase the electrical current of the heart.

Figure 2. Pacemaker implantation surgery.

The early 1960s made slow progress in the research and development of cardiac pacing technologies. The design by Greatbatch began to exhibit structural problems, such as broken leads, battery life depletion to only three years, dislodgements of the myocardial lead and a collection of fluid in the pulse generator, despite being coated with an epoxy resin. In addition, these types of early-pacing cardiac pulse generators were only capable of generating a fixed-rate pulse to the atria and ventricles, which posed issues by competing with the heart’s natural beat. The inability of these early devices to synchronize with the heart’s natural beat mechanisms increased the risk of patients to experience arrhythmias and ventricular fibrillation when these devices were implanted.

The Demand Pacemaker

In the mid-1960s, Berkovits designed a pacemaker built with a sense amplifier that could detect spontaneous heart activity. Figure 4 illustrates the basic principles of the functional pathway of the Demand pacemaker. With this pacing device, the sense amplifier receiving this impulse could amplify and normalize the signal, thereby preventing an artificial signal from arising as a result of intrinsic heart activity. The placement of additional electrodes within the myocardium also played a role in monitoring the intrinsic activity of the heart (i.e., ventricular depolarization [R-wave]).

Figure 4. Demand pacemaker – functional pathway. Credit: Sandro A.P. Haddad, Wouter A. Serdijn. (2009). Ultra-Low-Power Biomedical Signal Processing. An Analog Wavelet Filter Approach for Pacemakers. Springer Science and Business Media B.V.

Berkovits evolved his Demand pacemaker into a more sophisticated dual-chamber pacemaker. This latter development was designed to have two pacing leads that were placed in the right atrium and right ventricle. The main principle behind this design was to monitor electrical impulse activity in the atrium and anticipate whether pacing would be required to synchronize this electrical activity with the heart’s intrinsic impulse activity. This device would go on to benefit patients with a complete atria-ventricular block, a condition where there is very little heart activity and high demand for a pacemaker to mimic A-V electrical activity.

Modern Pacemakers

In addition to the development of Demand and dual-chamber pacemakers, various advancements in this field have expanded the life span and capabilities of modern pacemakers. For example, titanium has replaced previous casing materials that were composed of epoxy resin and silicon rubber. Additionally, during the 1980s, steroid-eluting leads were developed to decrease any inflammatory response that could result from the continual use of pacemakers. By reducing inflammation and the potential for scar tissue to form, the efficacy of pacemakers also improved. Recent design advancements in pacemaker technology have reduced the discomfort of these devices, as well as the need for patients to undergo additional surgeries and invasive procedures.

Conclusion

As discussed, early pacing devices were often crippled with problems associated with the device mimicking the intrinsic heartbeat without utilizing proper sensing tools capable of tracking spontaneous heart rhythm. In fact, one of the main issues of early pacing devices was attributed to the painful, invasive procedures that were required to power the heart pulse with an electronic device. However, throughout the late 1900s, research into the design of cardiac pacing devices allowed this technology to progress to the application of implantable devices that, with a transvenous lead, not only generate regular impulses to the heart muscle but are also capable of tracking and recording spontaneous intrinsic heartbeats.

References:

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This article was updated on 22^nd February, 2019.