The electric heart

Angeliki Asimaki was fifteen when, in 1997, she received a pacemaker after being diagnosed with intermittent atrioventricular block, which could cause her heart to stop for as long as thirteen seconds. The experience led her to become a researcher: today, she studies new ways of preventing sudden cardiac death in children. Miracle Santiago’s story, instead, begins at birth. A pacemaker saved her life after she was diagnosed with a rare heart defect. Forty years later, in 2025, she underwent a complex procedure to replace her pacing system, and came through it successfully. Then there is “Marco” (not his real name), a boy from Bergamo who suffered sudden episodes of asystole. In 2019, at the age of fourteen, he received a wireless micro-pacemaker, no larger than a coin.

There are thousands of stories like these: people of every age and background whose lives have been saved by a tiny device that monitors the heart’s rhythm and, when necessary, delivers the electrical impulse that keeps it beating. And if we were to connect all these stories with a single thread, to trace their origin, we could go back as far as late-eighteenth-century Bologna, when a doctor and scientist, Luigi Galvani conducted strange experiments using frog legs and electrostatic machines.

Animal electricity

“What Galvani was seeking was a comprehensive understanding of the phenomenon of life, building a bridge between the ancient science of anatomy and the new physics. His experiments were among the first to show that an electric current can pass through the body and produce a physiological response: they demonstrated that the body is a conductor, and that electricity can be received, transmitted and transformed into movement”, Eugenio Bertozzi explains. A professor at the Department of Physics and Astronomy - DIFA “Augusto Righi” and scientific advisor of the Physics Collection of the University Museum Network, he is responsible for the collection housed in the historic rooms of Bologna’s former Institute of Sciences, where the instruments used by Galvani and other scientists of his time are preserved.

A physician, anatomist and lecturer at the University’s Studium, as well as keeper of the Institute of Sciences’ anatomical chambers, Luigi Galvani worked in a scientific environment where anatomy and physics were beginning to converge. He began experimenting with frogs towards the end of the 1770s, dissecting them to study their nervous and muscular systems. 

His most famous experiments involved connecting the crural nerve to the leg muscle with metal arcs. When the two came into contact, the muscle contracted sharply, as if jolted by an electric shock. But Galvani went further. During thunderstorms, he hung frog legs from the railing of a terrace. On other occasions, he placed a frog in a room connected by a metal wire suspended from the ceiling to an electrical machine in the adjoining room.

“By moving the frog into another room and connecting it with a horizontal wire, Galvani and his collaborators were testing whether the effect could be transmitted over a distance,” Bertozzi explains. “They found that whenever a spark flew from the electrical machine, the frog in the other room contracted.”

A natural rhythm

“All the components of the cardiac muscle have electrical properties: the fibres of the conduction system are specialised, but even the working muscle tissue can spontaneously generate a rhythm,” explains Igor Diemberger, a professor at the Department of Medical and Surgical Sciences at the University of Bologna, director of the Specialisation School in Cardiovascular Diseases and a cardiologist at the Cardiology Unit of IRCCS Policlinico di Sant’Orsola.

One of the key structures is the sinus node, located where the superior vena cava enters the heart. It is where the normal heartbeat originates, which is why it is also known as the heart’s “natural pacemaker”. The electrical impulse that starts here spreads through the atria and reaches the atrioventricular node at the centre of the heart, where it slows down before travelling on to the ventricles. This delay is not a flaw but part of the heart’s natural rhythm: the atria contract first, helping the ventricles fill, and the ventricles then contract to pump blood around the body.

When the sinus node generates impulses too slowly, or the conduction system fails to transmit them to the ventricles, the heart rate can fall low enough to cause fatigue, dizziness or fainting. The tissues downstream of the problem may generate an emergency rhythm, but this is generally slow and less able to adapt to physical exertion. This condition is known as bradyarrhythmia, and this is where the pacemaker comes in.

“Bradyarrhythmias can result either from a problem with the generation of the electrical impulse, when the sinus node is affected, or with its transmission, when the problem involves the atrioventricular node or the conduction system,” Diemberger explains. “In the presence of an atrioventricular block, the underlying spontaneous rhythm can fall to as low as thirty beats per minute. In such cases, implanting a pacemaker ensures a heart rate compatible with everyday life.”

Pacing and sensing

In 1958, Swedish engineer Arne Larsson found himself in this situation. Following a viral infection, his heart rate fell as low as 28 beats per minute, and he would lose consciousness twenty to thirty times a day, with almost no chance of survival. He became the first patient to receive a pacemaker: at the time, the technology was still experimental, but it enabled him to leave hospital and go on to live for a long time. Over the years, he received more than twenty different devices, as the batteries initially had limited capacity. Yet he lived until 2001, dying at the age of 86 from melanoma.

Today, a conventional pacemaker consists of a generator placed under the skin, usually below the collarbone, and one or more leads, wires inserted through a vein and into the heart. The generator contains the battery, circuitry and software, while the lead delivers the electrical impulse to the myocardium, the muscle tissue that forms the heart’s central wall, and relays the heart’s spontaneous electrical signals back to the device. 

“The two fundamental functions of a pacemaker are pacing and sensing: the device detects the heart’s intrinsic rhythm and, according to its programmed settings, decides when an electrical impulse needs to be delivered,” Diemberger explains. “But the pacing circuit comprises more than just the pacemaker and the lead: it also includes the patient’s tissue. If the tissue at the site of the lead is damaged, the entire system may fail.”

The key word, then, is “sensing”. The device compares the signal it detects with its programmed settings and intervenes when a heartbeat is absent or occurs too late. This is also why pacemakers are equipped with motion and respiratory sensors, which can increase the heart rate during physical activity. The latest devices can also record arrhythmias, detect potential interference and monitor physiological parameters that can help track conditions such as heart failure.

Future and past

When the first pacemakers were introduced, battery life was the main challenge, making repeated replacements necessary. Today, however, thanks to new materials and algorithms that optimise power consumption, a pacemaker can last as long as fifteen or even twenty years. The focus has therefore shifted to the leads, which can fracture, become infected or become encased in fibrous tissue, sometimes requiring complex procedures to remove them. This has given rise to one of the most visible strands of recent innovation: the leadless pacemaker, a device no larger than a coin that is implanted directly in the heart, without transvenous leads or a subcutaneous pocket. But technological innovation is already looking further ahead.

“Solutions capable of self-recharging pacemakers are being developed, and systems have been developed in which a small electrode in the left ventricle is activated externally using ultrasound and piezoelectric crystals,” Diemberger says. “But every new technology has its advantages and limitations. In cardiac pacing, there must always be a balance between the energy delivered, safety, battery life, electrode stability and the patient’s needs, in order to provide increasingly personalised treatment.”

It is difficult to imagine that these extraordinary advances in medicine could have begun with little more than curious experiments involving prepared frogs and electrical machines. And yet, some of the credit for this revolution does belong to the young Bolognese doctor who sought to forge connections between physics and anatomy. Eugenio Bertozzi has no doubts on this point: “We certainly cannot credit Luigi Galvani with inventing the pacemaker, or with anticipating developments that his experiments could never have contained. But his work undoubtedly opened paths that, over the following two centuries, would lead to the study of cellular electricity and the therapeutic use of electrical impulses.”