The Long List of Inventions and Observations that Led to the Pacemaker

Pulse Theory and Observations that Bradycardia Leads to Syncope

Today physicians and athletes routinely measure the pulse. Although it is fairly simple to measure, especially compared to our now sophisticated imaging tools like magnetic resonance imaging, the pulse is still considered one of the "vital" signs. The knowledge that the pulse was a critical sign of health goes back to the ancient Egyptians. In 1875 George Ebers purchased an Egyptian scroll written in 1553 BC that described the relationship between the pulse in various locations and the heart beat.2

By 317 AD, the Chinese went further and developed a system of pulse analysis that was in some ways more complex than our own. They observed pulse at 11 locations and measured pulse rate variability (or lack of it) differences in pulses in different limbs. Wang Su-He observed that if the pulse became perfectly regular "the patient will be dead in four days."3'4 These were just two cultures that incorporated "pulse theory" as a key component of health care.

More recently, in 1580, Italian born Geronimo Mercuariale noted that a slow pulse was associated with syncope. In particular, he noted that patients that had either episodic or chronically low pulses while awake seemed more likely to have syncope. He did not, however, actually check the pulse during syncope, and thus could not show that the low pulse actually caused syncope.5 That observation would have to wait two centuries until in 1761 Giovanni Morgagni, another Italian, noted a patient during syncope had a slow pulse.

Shortly thereafter, Irish physicians Robert Adams and William Stokes described in separate publications patients who had low pulses and syncope. They also noted that bradycardia leads to dizziness, short pauses to more dizziness, and longer pauses to visual aura, then to complete syncope, convulsions, and finally death. In other words, longer pauses led to more symptoms. Although, Morgagni and Mercuariale had already made less detailed observations, Stokes and Adams are generally credited with the observation that syncope could have bradycardic instead of neurologic origin.6

However, it was not clear how one could increase the pulse. It was also unclear that electricity could be used to change the pulse.

In 1783 Luigi Galvani was dissecting frog legs on the same table where he had previously done work on static electricity. When an errant spark from a scalpel hit the sciatic nerve, the frog leg moved. Later observations, both with frog legs and later hearts, showed that electricity could stimulate muscle. He published these observations in 1791 as "Commentary on the Effect of Electricity on Muscular Motion."7 This may in part have served as an inspiration for Mary Shelley's novel Frankenstein..8

In 1800 Marie Bichat was able to stimulate the cardiac ventricles in patients soon after execution. Later in 1803 Pierre-Hubert Nysten observed that contractility of the left ventricle faded first and after death, while the right ventricle would contract with electrical stimulation 1 h after death. The atria would contract the longest. These observations were the first to show that direct electrical stimulation of the heart could lead to muscular contraction.

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