The science in heart beats and pacemakers
The Greek physician Aelius Galen (129AD-210) at the time of the Roman Empire was aware that a heart removed from the body continued to beat but was puzzled how this could be.
The purpose of the heart is to pump blood through the body since blood provides the oxygen and nutrients to sustain life – blood also transports metabolic waste for subsequent disposal. The human heart comprises four chambers. Looking down at your heart, the two adjacent top chambers are called the right atrium and the left atrium.
Directly below the atria are the right ventricle and left ventricle respectively. The atria fill with blood to the heart via veins and act as primers to the pumping action of the ventricles. The ventricles are pumping chambers that are connected to the arteries and send blood out of the heart.
The right atrium receives blood low in oxygen which is then passed (down) to the right ventricle and pumped from there to the lungs to be re-oxygenated and have carbon dioxide removed. The left atrium receives fresh oxygenated blood from the lungs which is then passed to the left ventricle and pumped into the circulation system to the body’s organs.
In 1839 Czech physician Jan Evangelista Purkinje discovered a series of branch-like fibres dispersed in the ventricles of the heart, now called the Purkinje fibres, but couldn’t establish their function. In the 1880s, Walter Gaskell was aware of the formation of heart electrical impulses and noted that electrical conduction proceeded as a wave from the atria to the ventricles.
In 1893 Swiss scientist, Wilhelm His, described a muscular bridge that connected the atria to the ventricles, but again, didn’t know its function.
The fog of ignorance on how the heart managed to beat, was lifted somewhat in 1903 by Japanese researcher Sunao Tawara. He discovered a group of specialist cells which electrically connects the right atrium and the right ventricle. This connection point is called the Atrio-Ventricular node (AVN). The AVN coordinates the electrical impulse passing through the top of the heart.
It wasn’t until 1907 when the puzzle of heart beat was solved. That was the year Martin Flack, a medical student, discovered that the heart had a natural pacemaker, another group of specialist cells called the Sino- Atrial Node (SA Node).
This is located in the wall of the right atrium. These cells have the ability to spontaneously generate an electrical impulse which surges through the heart’s electrical conduction system, this system includes, the AVN, the Bundle of His and the network of Purkinje fibres. The SA Node sets the rhythm of the heart, which is promoted by the other constituents of the heart’s electrical conduction system, and results in the contraction of the ventricles and the beating of the heart.
Martin Flack’s mentor, who shared the credit for the discovery, was Sir Arthur Keith. Sir Arthur Keith was something of a scoundrel, he had highly racist views and was heavily implicated in the Piltdown Man hoax of 1912.
Patients whose hearts cannot maintain an adequate heart beat or who have a block in the electrical conduction system can be assisted with an artificial pacemaker. The first pacemaker was produced in 1926 and involved a skin pad soaked in salt solution plus a needle inserted into the required heart chamber.
The power was supplied via a standard plug to the mains. By the 1950s a portable pacemaker had been developed in which two electrodes were attached to the heart, the power being supplied by a 45kg lead-acid battery. In the late 50s transistor technology made it possible for an implantable pacemaker to be manufactured.
The first patient was Swede, Arne Larsson, who was the beneficiary of 26 different pacemakers, each a step up in technology. He died at the age of 86 out living both his surgeon and the inventor of the implantable pacemaker device.
The latest pacemaker is so small, it can be inserted via a leg catheter. Many brands of modern pacemakers have a battery life of up to 15 years - a far cry from the first implanted pacemaker which had lasted for three hours before it experienced mechanical problems.