1. The Light of Stars
When we look at the visible stars in the sky at night what are we seeing? We see photons that have been released from the surface of a star and have travelled through space in a straight line until they reach the retina. For stars that are visible with the naked eye we are seeing photons that left those stars between 1000 and 10,000 years ago. During that time our understanding of the physical basis of the universe, the earth and of life (both visible and invisible) has gone from an amalgam of religion, magic, myth and ordinary observation to one based on scientific knowledge.
When we look at a electrocardiogram (ECG) what are we looking at? We see a line that has been traced on moving graph paper. We are taught that this line (in simple terms) is due to electrical activity in the heart.
Many introductions to the ECG begin with a drawing of a cell that has a potential difference across its cell membrane. The discussion then segues into topics such as resting membrane potential, action potential, depolarization, repolarization, channels in the cell membrane, vectors, leads and vectors. Then the discussion returns to the ECG tracing and the terminology of waves, intervals, points, shapes etc.
This approach focuses on a brief (recent) period of our knowledge about the heart and electrical phenomena, and ignores the several thousand years of speculation and observation that preceded what I will call the “Steam Punk” (nineteenth century) phase of cardiac electrophysiology. To use the analogy of photons, this is like focusing on the time taken for photons from the sun to reach the earth (8 minutes) and to be reflected off an ECG tracing into our retina, and ignoring the thousands of years it takes photons from visible stars in other galaxies to reach the earth.
The following sections provide anoverview of our understanding of the world and the heart in the “pre Steam Punk” era.
2. In the Beginning: Practical Knowledge of the Cardiovascular System
Persons who followed the trade of a butcher or a soldier (or a priest) knew that the bodies of all the higher animals contain a hot red fluid - the blood. They would have noted that underneath some parts of the skin there are pulsating tubes - the arteries. Bright red blood spurts out if the arteries are cut or divided. Under the surface of the skin there are other tubes which do not pulsate and are bluish in colour - these are the veins. If the veins are cut or divided darker blood flows out without pulsation. Anyone who has seen a recently killed animal opened knows that these two kinds of tubes join a midline structure in the lower chest, which in recently killed animals is still pulsating.
The pulsating heart within the chest was an enigma and mystery: it was linked to life and death, but different cultures also gave it spiritual, magical and symbolic qualities. The Egyptians made sure that a dead person had his heart with him when entering the afterlife, and the Aztecs in Mesoamerica cut the heart out of the the chest of living people and offered it (still beating) to their gods.
3. Preliterate Societies
Members of preliterate societies must, of necessity, have developed a shared knowledge of natural phenomena in the physical world. The observed natural phenomena would have included static electricity and naturally occurring magnetism (the lodestone). They would also be aware of the habits of animals, the properties of plants and the phases of human life (including the effects of injury and illness). This knowledge would be by observation and trial and error
The first written evidence of such knowledge appears in the river-valley civilizations of Egypt and Mesopotamia, commencing sometime around 3500 to 3000 BCE. These writings reveal a great emphasis on mythology and religion as explanations for the creation of the world and its operations, but there is also a practical interest in astronomy, mathematics and medicine. The documents known as the Ebers and Smith papyri (which probably date from the seventeenth and the sixteenth centuries BCE) mention the pulse and describe a variety of injuries and their likelihood of recovery.
4. The Feather and the Heart
The Egyptian Book of the Dead (about 1275 BCE) describes and illustrates the role of the heart in a person’s afterlife. The Egyptians thought that a person’s heart showed all their good and bad deeds. In the afterlife the heart was placed on scales and weighed by the god Anubis against the feather of truth. Thoth, the god of truth, checked that the weighing was fair. If the heart was lighter than the feather the dead person continued into the next world. If the heart was heavier then the person was eaten by the Devourer, a monster that was part-lion, part-hippopotamus and part-crocodile.
When we look at an ECG today (over 3000 years since the Book of the Dead was written) we echo the actions of Anubis; we are assessing the goodness of badness of a person’s heart using our knowledge and analysis skills (the “feather of truth”).
5. First Principles: Where Do We Come From ?
At some stage every person thinks about concepts such as self, matter, cause, identity, time, and space. In 1897 Paul Gauguin (1848-1903) produced a magnificent painting with the evocative title of “Where Do We Come From? What Are We? Where Are We Going?”, which sums up these metaphysical concepts. Why discuss a painting completed in 1897? This year was an important in the development of the ECG, because in May 1887 Dr Augustus D Waller recorded the first human electrocardiogram at St Mary's Hospital, London.
Paul Gauguin was a influential French painter who worked with many artists, including Vincent van Gogh and Edgar Degas. He lived in various exotic overseas locations, including the Caribbean Island of Martinique in 1887.
Eight years later, in 1895, Gauguin boarded the steamship Australian at Marseilles on a voyage that took him to Sydney and Melbourne in Australia, from where he went to Auckland, New Zealand, and finally, for the second time, to Tahiti. Although it is tempting to romanticise the life of an artist in a primitive society, the reality was different:
“Instead of Paradise, Gauguin found a colony; instead of Noble Savages, prostitutes; instead of the pure children of Arcadia, listless half-breeds - a culture wrecked by missionaries, booze, exploitation, and gonorrhea, its rituals dead, its memory lost, its population down from forty thousand in Cook’s time to six thousand in Gauguin’s time” (Robert Hughes. The Shock of the New - Art and the Century of Change. British Broadcasting Corporation 1980).
Initially Gauguin prospered, but in 1897 illness, poverty and the sudden death of his daughter drove him to consider suicide. Before taking his own life, however, he resolved to paint one last canvas to summarize his entire artistic and personal experience. Its subject would be the meaning of human existence.
Lacking the money to buy canvas, he tore open several sacks, stitched them together, and stretched them out - full four and a half meters long and one meter seventy high. The painting was completed in a month.
There are 12 figures in the painting (eight women, two men, and two children) and an assortment of domesticated animals. The key to the entire work is in three of the figures: the newborn on the extreme right, the erect figure in the centre, and theold woman on the lower left-hand side. They epitomize the beginning, the culmination, and the closing of one round of the cycle of life.
6. Metaphysics and the Material World
The Greeks: Fire and Rain
The earliest records we have of speculations about the physical nature of our world date from the seventh century BCE, and originate in Greece. Such enquiries about the nature of the physical world or universe were called natural philosophy, a term that was in common use until the nineteenth century when it was replaced by the concept of “science”.
The attempts of these early Greek philosophers to explain the nature of matter are important because they did not invoke a divine cause, and because some of them anticipated features of modern science. However none of them attempted to verify or justify their speculations. Stephen Weinberg says that “... to understand these early Greeks, it is better to think of them not as physicists or scientists or even philosophers, but as poets”. (Stephen Weinberg. To Explain the World. The Discovery of Modern Science. 2015 Allen Lane).
We begin with the Ionian School. By the sixth century BCEthe western coast of what is now Turkey had been settled by Greeks speaking the Ionian dialect. The richest and most powerful of the Ionian cities was Miletus. Three important natural philosophers came from Miletus.
Thales (640 − 546 BC) is credited with knowing that amber, when rubbed, will attract light objects. Thales also apparently was aware that a certain mineral (now called magnetite, or lodestone) will attract small pieces of iron. Finally, Thales was said to believe that all matter is composed of a single fundamental substance: water. Water is an interesting candidate for a fundamental substance: it is essential for life, normally occurs as a liquid but can be easily converted into a solid by freezing or into a vapour by boiling.
Anaximander, the second Milesian, was in his sixties about 546 BCE. He held that all things come from from a single primal substance which was not water or any other substance that we know. Anaximander is said to have been the first man to make a map, and he believed that the earth was shaped like a cylinder.
The third Milesian, Anaximenes, lived in the period after Anaximander and before the destruction of Miletus in 494 BC. He believed the fundamental substance was air; fire was rarefied air, condensed air becomes water, and condensed water becomes earth and then stone.
At Ephesus, not far from Miletus, Heraclitus (500s BCE) taught that the fundamental substance is fire. During the next century Empedocles (400s BCE) showed that air was a separate substance by noting that when a bucket is put upside down into water, the water does not enter into the bucket. Empedocles also proposed that the world is made of four elements: air, water, earth, and fire. According to Bertrand Russell: “The chemistry of the ancients stopped dead at this point. No further progress was made in this science until the Mohammedan alchemists embarked upon their search for the philosopher’s stone, the elixir of life, and a method of transmuting base metals into gold”. (History of Western Philosophy. Bertrand Russell. 1946. Reprinted in Routledge Classics 2004 )
We take for granted the atomic basis of matter, although the scientific acceptance of the atomic nature of matter did not occur until the nineteenth century. The structure of an “atom” is now a familiar cultural icon; in the 2009 superhero movie “Watchmen” one of the heroes (Dr Manhattan) has the basic structure of an atom (a nucleus and a circling electron) etched on his forehead.
The metaphysical concept of atomism emerged in Ancient Greece as a philosophical arguments about the ultimate nature of material reality. Leucippus, who lived during the fifth century BCE, is regarded as the founder of atomism in ancient Greek philosophy. Democritus (born about 460 BC) extended the system originated by Leucippus. He believed that there are two different kinds of realities in the natural world, atoms and void. Atoms are infinite in number and various in size and shape, and perfectly solid, with no internal gaps. They move about in an infinite void, repelling one another when they collide or combining into clusters by means of tiny hooks and barbs on their surfaces, which become entangled.
The visible objects in our world are really clusters of these atoms; changes in the visible objects are caused by rearrangements or additions to the atoms composing them. While the atoms are eternal, the objects compounded out of them are not.
7. Elizabethan Era & the Scientific Revolution
8. The Electric Enlightenment
9. The ECG & Steam-Punk
Steampunk is a subgenre of speculative fiction set in a quasi-Victorian alternative history. It incorporates technology and aesthetic design in a world where steam power is the main source of energy, often combined with retro-futurist inventions. In one such reality Einstein and Sherlock Holmes collaborate with Einthoven and Julius Bernstein in the development of the ECG and television.
Getting to the Point of Steam Punk ECG
Matteucci and the Induced Contraction
How do nerves work? The standard answer by natural philosophers until well into the seventeenth century was that they produced their effect by the flow of “animal spirits”. In the seventeenth century Descartes suggested that the animal spirits might be a real fluid that flowed through hollow nerves into muscles. By the early nineteenth century the theory of animal spirits was largely discarded, although remnants of the theory lingered:
Matteucci devised an experiment (which he called ‘induced contraction’) that suggested a link between electrical charge on the surface of a muscle and excitation of a nerve.
“ Having prepared a galvanoscopic frog, we place its nerve upon one or both thighs of a frog placed in the ordinary manner: then, by applying the two poles of a [voltaic] pile to the lumbar plexus of this frog, we observe that when the muscles of the thighs contract, convulsions simultaneously occur in the galvanoscopic claw, whose nerve rests upon the thighs in contraction”.
Du Bois_Reymond and the ‘Injury Current’
Emil Du Bois_Reymond observed a flow of current if a galvanometer was connected between the intact outer surface and the cut surface of a unstimulated muscle. This was called the ‘injury current’, and corresponds to our current terminology of resting membrane potential. He deduced that the outer surface of the cell was positively charged compared to the inside of the cell.
Using electrical stimuli to activate the nerve or muscle, du Bois-Remond found a temporary decrease in the injury current that he termed “negative variation”. At about the same time, in 1850, Helmholtz found that the conduction speed of the “excitatory process” in nerve-muscle preparations was about 30m/s. But it was not clear whether Helmholtz’s “excitatory process” and du-Bois’ “negative variation” were conducted at the same speed.
The Action Potential
In 1868 Jules Bernstein provided the first accurate description and measurementof the “negative variation” (action potential) in frog nerve. He showedthat the velocity of transmission ofan action potential was about the same as the velocity of transmission of a nerve impulse.
In 1872 Ludimar Herman suggested that the propagation ofa nerve impulse was due to localcurrents between the stimulatedregion of the nerve and the adjacent (unstimulated) nerve. The correctness of the local circuit hypothesis was demonstrated by Alan Hodgkin in 1939.
The Membrane Theory
Julius Bernstein published his Membrane Theory in 1902, which was the first plausible, physico-chemical explanation of bioelectric events. This involved combining an equation and a hypothesis:
1. The Nernst equations were used to predict the electrical potentials from concentration gradients of electrolytes. These predicted values werecompared with the “injury or resting current” that was measured in nerve and muscle
2. Wilhelm Ostwald (1853–1932) suggested that the electrical potential across that develop across artificial semipermeable membranes was due to their selective permeability to ions.