How electricity learned to correct the rhythm of the human heart

For Hugo von Ziemssen, a German physician, it was a rare opportunity to mechanically and electrically stimulate a living heart; in this way, it became clear that electricity could act on the heart. Earlier researchers such as Aldini had believed that the only way to achieve this was through the nervous system.

During experiments on Serafin's heart, Ziemssen observed that when periodic pulses of direct current (the same current that Volta had generated with his battery) were applied at a frequency just above the natural heartbeat, the heart tried to follow the rhythm of that artificial metronome. This indicated that a defective heartbeat could be overridden, or a stopped one restarted, by sending artificial electrical impulses to the point at the top of the heart where the natural electrical signal originates. But the results were not significant. The method worked only when the electrode was placed directly on the exposed surface of the heart; applying the impulse to an intact chest was useless. And since nobody was rushing to have their body opened so that electrical shocks could be applied to the heart, the idea had no practical prospects.

It took another thirty years before the medical knowledge acquired led to practical applications. Progress came with the spread of the electrical grid in the United States, which had caused a sharp increase in accidents involving electric shocks; it was precisely the kind of «temporary death» that Aldini had tried to reverse more than a century earlier. The matter had become urgent. It was clear that the heartbeat could be restarted or corrected; the next question was how to maintain it. Work began on a device that could continuously override the heartbeat. And that device was truly terrifying.

It was about the size of a small suitcase, weighed 7.2 kilograms, and worked with a hand crank. A cable sent the generated electricity to a needle that penetrated the heart. The whole thing worked, but obtaining permission to conduct clinical studies was difficult. It was crucial to find the right place to insert the needle; a mistake caused fatal bleeding. In 1932, the American Medical Association openly condemned the device and Albert Hyman, who had created it, arguing that the supposed resuscitations through such injections into the heart should be «classified as miracles». The skepticism was due to the fact that, after years of experiments like Aldini's, widespread caution had taken hold, and no American industrialist wanted to risk their reputation by helping Hyman produce his device.

Nevertheless, by 1950 other doctors, who clearly felt the need for such a machine and could now rely on more advanced materials, had improved its design. What was achieved was not always a genuine improvement. The device had to be dragged around on a small cart together with its tangle of cables. Sometimes it had to be connected to the electrical grid (and all the worse if the power went out, which was not such an uncommon problem). The first attempts to understand how to make it implantable (the final frontier of portability) required a better source of energy than those available.

In 1958, Wilson Greatbatch found a long-lasting energy source that was less troubling than plutonium: he invented a pacemaker that used a lithium-ion battery, like most current models. Within twenty years, his invention had been refined into the small implantable gadget that corresponds to the modern idea of a pacemaker.

The most common use of a pacemaker is to speed up a heartbeat that is too slow (as in bradycardia). The tiny lightning bolt overrides the heart's own bioelectricity, regularly applying tiny electric shocks to make the heart function at the right rhythm.